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Seat belt

A seat belt, also known as a safety belt or spelled seatbelt, is a vehicle safety device designed to secure the driver or a passenger of a vehicle against harmful movement that may result during a collision or a sudden stop. A seat belt reduces the likelihood of death or serious injury in a traffic collision by reducing the force of secondary impacts with interior strike hazards, by keeping occupants positioned correctly for maximum effectiveness of the airbag (if equipped), and by preventing occupants being ejected from the vehicle in a crash or if the vehicle rolls over.

When in motion, the driver and passengers are traveling at the same speed as the vehicle. If the vehicle suddenly stops or crashes, the occupants continue at the same speed the vehicle was going before it stopped. A seat belt applies an opposing force to the driver and passengers to prevent them from falling out or making contact with the interior of the car (especially preventing contact with, or going through, the windshield). Seat belts are considered primary restraint systems (PRSs), because of their vital role in occupant safety.

Effectiveness
An analysis conducted in the United States in 1984 compared a variety of seat belt types alone and in combination with air bags. The range of fatality reduction for front seat passengers was broad, from 20% to 55%, as was the range of major injury, from 25% to 60%. More recently, the Centers for Disease Control and Prevention has summarized these data by stating "seat belts reduce serious crash-related injuries and deaths by about half." Most malfunctions are a result of there being too much slack in the seat belt at the time of the accident.

It has been suggested that although seat belt usage reduces the probability of death in any given accident, mandatory seat belt laws have little or no effect on the overall number of traffic fatalities because seat belt usage also disincentivizes safe driving behaviors, thereby increasing the total number of accidents. This idea, known as compensating-behavior theory, is not supported by the evidence.

In case of vehicle rollover in a U.S. passenger car or SUV, from 1994 to 2004, wearing a seat belt reduced the risk of fatalities or incapacitating injuries and increased the probability of no injury:
 * In case of vehicle rollover in a U.S. passenger car, there are % fatalities in 1994 and % in 2014 when user is restrained. There are % fatalities in 1994 and % in 2014 when the user is unrestrained.
 * In case of vehicle rollover, there are % incapacitating injury in 1994 and % in 2014 when the user is restrained. There are % incapacitating injury in 1994 and % in 2014 when user is unrestrained.
 * The probability of no injury is % in 1994 and % in 2014 when the user is restrained. There were % no injury in 1994 and % in 2014 when the user is unrestrained.

History
Seat belts were invented by English engineer George Cayley, to use on his glider, in the mid-19th century.

In 1946, C. Hunter Shelden opened a neurological practice at Huntington Memorial Hospital in Pasadena, California. In the early 1950s, Shelden made a major contribution to the automotive industry with his idea of retractable seat belts. This came about from his care of the high number of head injuries coming through the emergency room. He investigated the early seat belts with primitive designs that were implicated in these injuries and deaths.

Nash was the first American car manufacturer to offer seat belts as a factory option, in its 1949 models. They were installed in 40,000 cars, but buyers did not want them and requested that dealers remove them. The feature was "met with insurmountable sales resistance" and Nash reported that after one year "only 1,000 had been used" by customers.

Ford offered seat belts as an option in 1955. These were not popular, with only 2% of Ford buyers choosing to pay for seat belts in 1956.

To reduce the high level of injuries Shelden was seeing, he proposed, in late 1955, retractable seat belts, recessed steering wheels, reinforced roofs, roll bars, automatic door locks, and passive restraints such as air bags be made mandatory. Glenn W. Sheren, of Mason, Michigan, submitted a patent application on March 31, 1955, for an automotive seat belt and was awarded in 1958. This was a continuation of an earlier patent application that Sheren had filed on September 22, 1952.

The first modern three-point seat belt (the so-called CIR-Griswold restraint) commonly used in consumer vehicles was patented in 1955 by the Americans Roger W. Griswold and Hugh DeHaven.

Saab introduced seat belts as standard equipment in 1958. After the Saab GT 750 was introduced at the New York Motor Show in 1958 with safety belts fitted as standard, the practice became commonplace.

Vattenfall, the Swedish national electric utility, did a study of all fatal, on-the-job accidents among their employees. The study revealed that the majority of fatalities occurred while the employees were on the road on company business. In response, two Vattenfall safety engineers, Bengt Odelgard and Per-Olof Weman, started to develop a seat belt. Their work was presented to Swedish manufacturer Volvo in the late 1950s, and set the standard for seat belts in Swedish cars. The three-point seat belt was developed to its modern form by Swedish inventor Nils Bohlin for Volvo, which introduced it in 1959 as standard equipment. In addition to designing an effective three-point belt, Bohlin demonstrated its effectiveness in a study of 28,000 accidents in Sweden. Unbelted occupants sustained fatal injuries throughout the whole speed scale, whereas none of the belted occupants was fatally injured at accident speeds below 60 mph. No belted occupant was fatally injured if the passenger compartment remained intact. Bohlin was granted for the device.

Subsequently, in 1966, Congress passed the National Traffic and Motor Vehicle Safety Act, requiring all automobiles to comply with certain safety standards.

The first compulsory seat belt law was put in place in 1970, in the state of Victoria, Australia, requiring their use by drivers and front-seat passengers. This legislation was enacted after trialing Hemco seat belts, designed by Desmond Hemphill (1926–2001), in the front seats of police vehicles, lowering the incidence of officer injury and death. Mandatory seat belt laws in the United States began to be introduced in the 1980s and faced opposition, with some consumers going to court to challenge the laws. Some cut seat belts out of their cars.

Material
The 'belt' part of the typical seatbelt seen in vehicles worldwide is referred to as the 'webbing'. Modern seat belt webbing has a high tensile strength, about 3000-6000lbs, to resist tearing at high loads such as during high-speed collisions or while restraining larger passengers.

While nylon was used in some early seat belts (and is still used for lap belts), it was replaced by 100% polyester due to its better UV resistance, lower extensibility and higher stiffness. Nylon was also prone to stretching much more than polyester, and was prone to wear and tear, with tiny abrasions drastically reducing tensile strength causing a lack of reliability in one of the most important safety measures in a vehicle. Seat belts are commonly 46 or 48 mm wide with a 2/2 herringbone twill weaving pattern to maximize the thread density. Modern seatbelt weaves also feature snag-proof selvedges reinforced with strong polyester threads to prevent the wear and tear, while remaining flexible. The weave features about 300 warp threads for every 46mm wide webbing, leading to around 150 ends per inch of webbing.

Accident investigators often examine the webbing of a seatbelt to determine if an occupant of a vehicle was wearing their seatbelt during a collision. The material of the webbing may contain traces of the occupant's clothing. Certain materials such as nylons may become permanently affixed or melted onto the fabric as a result of heat produced by friction, whereas fiber based clothing leaves no remains on modern webbing.

Two-point
A two-point belt attaches at its two endpoints. A simple strap was first used March 12, 1910, by pilot Benjamin Foulois,  a pioneering aviator with the Aeronautical Division, U.S. Signal Corps, so he might remain at the controls during turbulence.

The Irvin Air Chute Company made the seat belt for use by professional race car driver Barney Oldfield when his team decided the daredevil should have a "safety harness" for the 1923 Indianapolis 500.

Lap
A lap belt is a strap that goes over the waist. This was the most common type of belt prior to legislation requiring three-point belts and is found in older cars. Coaches are equipped with lap belts (although many newer coaches have three-point belts), as are passenger aircraft seats.

University of Minnesota professor James J. (Crash) Ryan was the inventor of, and held the patent for, the automatic retractable lap safety belt. Ralph Nader cited Ryan's work in Unsafe at Any Speed and, following hearings led by Senator Abraham Ribicoff, President Lyndon Johnson signed two bills in 1966 requiring safety belts in all passenger vehicles starting in 1968.

Until the 1980s, three-point belts were commonly available only in the front outboard seats of cars; the back seats were often only fitted with lap belts. Evidence of the potential of lap belts to cause separation of the lumbar vertebrae and the sometimes-associated paralysis, or "seat belt syndrome" led to the progressive revision of passenger safety regulations in nearly all developed countries to require three-point belts, first in all outboard seating positions, and eventually in all seating positions in passenger vehicles. Since September 1, 2007, all new cars sold in the U.S. require a lap and shoulder belt in the center rear seat. In addition to regulatory changes, "seat belt syndrome" has led to a liability for vehicle manufacturers. One Los Angeles case resulted in a $45 million jury verdict against Ford; the resulting $30 million judgment (after deductions for another defendant who settled prior to trial) was affirmed on appeal in 2006.

While lap belts are exceedingly rare to spot in modern cars, they are the standard in commercial airliners. The lift-lever style of commercial aircraft buckles allows for the seatbelt to be easily clasped and unclasped, accessible quickly in case of an emergency where a passenger must evacuate, and fulfills the minimum safety requirements provided by the FAA while remaining low-cost to produce. Furthermore, in case of any collision, a passenger in economy class has only around 9 inches for their head to travel forward, meaning restraining the torso and head is relatively unnecessary as the head has little room to accelerate before collision.

Sash
A "sash" or shoulder harness is a strap that goes diagonally over the vehicle occupant's outboard shoulder and is buckled inboard of their lap. The shoulder harness may attach to the lap belt tongue, or it may have a tongue and buckle completely separate from those of the lap belt. Shoulder harnesses of this separate or semi-separate type were installed in conjunction with lap belts in the outboard front seating positions of many vehicles in the North American market starting at the inception of the shoulder belt requirement of the U.S. National Highway Traffic Safety Administration's (NHTSA) Federal Motor Vehicle Safety Standard 208 on January 1, 1968. However, if the shoulder strap is used without the lap belt, the vehicle occupant is likely to "submarine", or slide forward in the seat and out from under the belt, in a frontal collision. In the mid-1970s, three-point belt systems such as Chrysler's "Uni-Belt" began to supplant the separate lap and shoulder belts in American-made cars, though such three-point belts had already been supplied in European vehicles such as Volvo, Mercedes-Benz, and Saab for some years.

Three-point
A three-point belt is a Y-shaped arrangement, similar to the separate lap and sash belts, but unified. Like the separate lap-and-sash belt, in a collision, the three-point belt spreads out the energy of the moving body over the chest, pelvis, and shoulders. Volvo introduced the first production three-point belt in 1959. The first car with a three-point belt was a Volvo PV 544 that was delivered to a dealer in Kristianstad on August 13, 1959. The first car model to have the three-point seat belt as a standard item was the 1959 Volvo 122, first outfitted with a two-point belt at initial delivery in 1958, replaced with the three-point seat belt the following year. The three-point belt was developed by Nils Bohlin, who had earlier also worked on ejection seats at Saab. Volvo then made the new seat belt design patent open in the interest of safety and made it available to other car manufacturers for free.

Belt-in-Seat
The Belt-in-Seat (BIS) is a three-point harness with the shoulder belt attached to the seat itself, rather than to the vehicle structure. The first car using this system was the Range Rover Classic, which offered BIS as standard on the front seats from 1970. Some cars like the Renault Vel Satis use this system for the front seats. A General Motors assessment concluded seat-mounted three-point belts offer better protection especially to smaller vehicle occupants, though GM did not find a safety performance improvement in vehicles with seat-mounted belts versus belts mounted to the vehicle body.

Belt-in-Seat type belts have been used by automakers in convertibles and pillarless hardtops, where there is no "B" pillar to affix the upper mount of the belt. Chrysler and Cadillac are well known for using this design. Antique auto enthusiasts sometimes replace original seats in their cars with BIS-equipped front seats, providing a measure of safety not available when these cars were new. However, modern BIS systems typically use electronics that must be installed and connected with the seats and the vehicle's electrical system in order to function properly.

4-, 5-, and 6-point
Five-point harnesses are typically found in child safety seats and in racing cars. The lap portion is connected to a belt between the legs and there are two shoulder belts, making a total of five points of attachment to the seat. A 4-point harness is similar, but without the strap between the legs, while a 6-point harness has two belts between the legs. In NASCAR, the 6-point harness became popular after the death of Dale Earnhardt, who was wearing a five-point harness when he suffered his fatal crash. As it was first thought that his belt had broken, and broke his neck at impact, some teams ordered a six-point harness in response.

Seven-point
Aerobatic aircraft frequently use a combination harness consisting of a five-point harness with a redundant lap belt attached to a different part of the aircraft. While providing redundancy for negative-g maneuvers (which lift the pilot out of the seat), they also require the pilot to unlatch two harnesses if it is necessary to parachute from a failed aircraft.

Locking retractors
The purpose of locking retractors (sometimes called ELR belts, for "Emergency Locking Retractors") is to provide the seated occupant the convenience of some free movement of the upper torso within the compartment while providing a method of limiting this movement in the event of a crash. Starting in 1996, all passenger vehicles were required to lock pre-crash, meaning they have a locking mechanism in the retractor or in the latch plate. Seat belts are stowed on spring-loaded reels called "retractors" equipped with inertial locking mechanisms that stop the belt from extending off the reel during severe deceleration.

There are two main types of inertial seat belt locks. A webbing-sensitive lock is based on a centrifugal clutch activated by the rapid acceleration of the strap (webbing) from the reel. The belt can be pulled from the reel only slowly and gradually, as when the occupant extends the belt to fasten it. A sudden rapid pull of the belt—as in a sudden braking or collision event—causes the reel to lock, restraining the occupant in position. The first automatic locking retractor for seat belts and shoulder harnesses in the U.S. was the Irving "Dynalock" safety device. These "Auto-lock" front lap belts were optional on AMC cars with bucket seats in 1967.

A vehicle-sensitive lock is based on a pendulum swung away from its plumb position by rapid deceleration or rollover of the vehicle. In the absence of rapid deceleration or rollover, the reel is unlocked and the belt strap may be pulled from the reel against the spring tension of the reel. The vehicle occupant can move around with relative freedom while the spring tension of the reel keeps the belt taut against the occupant. When the pendulum swings away from its normal plumb position due to sudden deceleration or rollover, a pawl is engaged, the reel locks and the strap restrains the belted occupant in position. Dual-sensing locking retractors use both vehicle G-loading and webbing payout rate to initiate the locking mechanism.

Pretensioners and webclamps

Seat belts in many newer vehicles are also equipped with "pretensioners" or "web clamps", or both.

Pretensioners preemptively tighten the belt to prevent the occupant from jerking forward in a crash. Mercedes-Benz first introduced pretensioners on the 1981 S-Class. In the event of a crash, a pretensioner will tighten the belt almost instantaneously. This reduces the motion of the occupant in a violent crash. Like airbags, pretensioners are triggered by sensors in the car's body, and many pretensioners have used explosively expanding gas to drive a piston that retracts the belt. Pretensioners also lower the risk of "submarining", which occurs when a passenger slides forward under a loosely fitted seat belt.

Some systems also pre-emptively tighten the belt during fast accelerations and strong decelerations, even if no crash has happened. This has the advantage that it may help prevent the driver from sliding out of position during violent evasive maneuvers, which could cause loss of control of the vehicle. These pre-emptive safety systems may prevent some collisions from happening, as well as reduce injuries in the event an actual collision occurs. Pre-emptive systems generally use electric pretensioners, which can operate repeatedly and for a sustained period, rather than pyrotechnic pretensioners, which can only operate a single time.

Webclamps stop the webbing in the event of an accident and limit the distance the webbing can spool out (caused by the unused webbing tightening on the central drum of the mechanism). These belts also often incorporate an energy management loop ("rip stitching") in which a section of the webbing is looped and stitched with special stitching. The function of this is to "rip" at a predetermined load, which reduces the maximum force transmitted through the belt to the occupant during a violent collision, reducing injuries to the occupant.

A study demonstrated that standard automotive three-point restraints fitted with pyrotechnic or electric pretensioners were not able to eliminate all interior passenger compartment head strikes in rollover test conditions. Electric pretensioners are often incorporated on vehicles equipped with precrash systems; they are designed to reduce seat belt slack in a potential collision and assist in placing the occupants in a more optimal seating position. The electric pretensioners also can operate on a repeated or sustained basis, providing better protection in the event of an extended rollover or a multiple collision accident.

Inflatable
The inflatable seat belt was invented by Donald Lewis and tested at the Automotive Products Division of Allied Chemical Corporation. Inflatable seat belts have tubular inflatable bladders contained within an outer cover. When a crash occurs, the bladder inflates with gas to increase the area of the restraint contacting the occupant and also shortening the length of the restraint to tighten the belt around the occupant, improving the protection. The inflatable sections may be shoulder-only or lap and shoulder. The system supports the head during the crash better than a web-only belt. It also provides side impact protection. In 2013, Ford began offering rear-seat inflatable seat belts on a limited set of models, such as the Explorer and Flex.

Automatic

Seat belts that automatically move into position around a vehicle occupant once the adjacent door is closed and/or the engine is started were developed as a countermeasure against low usage rates of manual seat belts, particularly in the United States. The 1972 Volkswagen ESVW1 Experimental Safety Vehicle presented passive seat belts. Volvo tried to develop a passive three point seat belt. In 1973, Volkswagen announced they had a functional passive seat belt. The first commercial car to use automatic seat belts was the 1975 Volkswagen Golf.

Automatic seat belts received a boost in the United States in 1977 when Brock Adams, United States Secretary of Transportation in the Carter Administration, mandated that by 1983 every new car should have either airbags or automatic seat belts. There was strong lobbying against the passive restraint requirement by the auto industry. Adams was criticized by Ralph Nader, who said that the 1983 deadline was too late. The Volkswagen Rabbit also had automatic seat belts, and VW said that by early 1978, 90,000 cars had sold with them.

General Motors introduced a three-point non-motorized passive belt system in 1980 to comply with the passive restraint requirement. However, it was used as an active lap-shoulder belt because of unlatching the belt to exit the vehicle. Despite this common practice, field studies of belt use still showed an increase in wearing rates with this door-mounted system. General Motors began offering automatic seat belts on the Chevrolet Chevette. However, the company reported disappointing sales because of this feature. For the 1981 model year, the new Toyota Cressida became the first car to offer motorized automatic passive seat belts.

A study released in 1978 by the United States Department of Transportation said that cars with automatic seat belts had a fatality rate of .78 per 100 million miles, compared with 2.34 for cars with regular, manual belts.

In 1981, Drew Lewis, the first Transportation Secretary of the Reagan Administration, influenced by studies done by the auto industry, dropped the mandate; the decision was overruled in a federal appeals court the following year, and then by the Supreme Court. In 1984, the Reagan Administration reversed its course, though in the meantime the original deadline had been extended; Elizabeth Dole, then Transportation Secretary, proposed that the two passive safety restraints be phased into vehicles gradually, from vehicle model year 1987 to vehicle model year 1990, when all vehicles would be required to have either automatic seat belts or driver side air bags. Though more awkward for vehicle occupants, most manufacturers opted to use less expensive automatic belts rather than airbags during this time period.

When driver side airbags became mandatory on all passenger vehicles in model year 1995, most manufacturers stopped equipping cars with automatic seat belts. Exceptions include the 1995–96 Ford Escort/Mercury Tracer and the Eagle Summit Wagon, which had automatic safety belts along with dual airbags.

Systems

 * Manual lap belt with automatic motorized shoulder belt: When the door is opened, the shoulder belt moves from a fixed point near the seat back on a track mounted in the door frame of the car to a point at the other end of the track near the windshield. Once the door is closed and the car is started, the belt moves rearward along the track to its original position, thus securing the passenger. The lap belt must be fastened manually.
 * Manual lap belt with automatic non-motorized shoulder belt: This system was used in American-market vehicles such as the Hyundai Excel and Volkswagen Jetta. The shoulder belt is fixed to the aft upper corner of the vehicle door and is not motorized. The lap belt must be fastened manually.
 * Automatic shoulder and lap belts: This system was mainly used in General Motors vehicles, though it was also used on some Honda Civic hatchbacks and Nissan Sentra coupes. When the door is opened, the belts go from a fixed point in the middle of the car by the floor to the retractors on the door. Passengers must slide into the car under the belts. When the door closes, the seat belt retracts into the door. The belts have normal release buttons that are supposed to be used only in an emergency, but in practice are routinely used in the same manner as manual seat belt clasps. This system also found use by American Specialty Cars when they created the 1991-1994 convertible special edition of the Nissan 240SX, a car that traditionally had a motorized shoulder belt.

Disadvantages
Automatic belt systems generally offer inferior occupant crash protection. In systems with belts attached to the door rather than a sturdier fixed portion of the vehicle body, a crash that causes the vehicle door to open leaves the occupant without belt protection. In such a scenario, the occupant may be thrown from the vehicle and suffer greater injury or death.

Because many automatic belt system designs compliant with the U.S. passive-restraint mandate did not meet the anchorage requirements of Canada (CMVSS 210) — which were not weakened to accommodate automatic belts — vehicle models that had been eligible for easy importation in either direction across the U.S.-Canada border when equipped with manual belts became ineligible for importation in either direction once the U.S. variants obtained automatic belts and the Canadian versions retained manual belts. Two particular models affected were the Dodge Spirit and Plymouth Acclaim.

Automatic belt systems also present several operational disadvantages. Motorists who would normally wear seat belts must still fasten the manual lap belt, thus rendering redundant the automation of the shoulder belt. Those who do not fasten the lap belt wind up inadequately protected only by the shoulder belt. In a crash, without a lap belt, such a vehicle occupant is likely to "submarine" (be thrown forward under the shoulder belt) and be seriously injured. Motorized or door-affixed shoulder belts hinder access to the vehicle, making it difficult to enter and exit—particularly if the occupant is carrying items such as a box or a purse. Vehicle owners tend to disconnect the motorized or door-affixed shoulder belt to relieve the nuisance when entering and exiting the vehicle, leaving only a lap belt for crash protection. Also, many automatic seat belt systems are incompatible with child safety seats, or only compatible with special modifications.

Homologation and testing
Starting in 1971 and ending in 1972, the United States conducted a research project on seat belt effectiveness on a total of 40,000 vehicle occupants using car accident reports collected during that time. Of these 40,000 occupants, 18% were reported wearing lap belts, or two-point safety belts, 2% were reported wearing a three-point safety belt, and the remaining 80% were reported as wearing no safety belt. The results concluded that users of the two-point lap belt had a 73% lower fatality rate, a 53% lower serious injury rate, and a 38% lower injury rate than the occupants that were reported unrestrained. Similarly, users of the three-point safety belt had a 60% lower serious injury rate and a 41% lower rate of all other injuries. Out of the 2% described as wearing a three-point safety belt, no fatalities were reported.

This study and others led to the Restraint Systems Evaluation Program (RSEP), started by the NHTSA in 1975 to increase the reliability and authenticity of past studies. A study as part of this program used data taken from 15,000 tow-away accidents that involved only car models made between 1973 and 1975. The study found that for injuries considered “moderate” or worse, individuals wearing a three-point safety belt had a 56.5% lower injury rate than those wearing no safety belt. The study also concluded that the effectiveness of the safety belt did not differ with the size of a car. It was determined that the variation among results of the many studies conducted in the 1960s and 70s was due to the use of different methodologies, and could not be attributed to any significant variation in the effectiveness of safety belts.

Wayne State University's Automotive Safety Research Group, as well as other researchers, are testing ways to improve seat belt effectiveness and general vehicle safety apparatuses. Wayne State's Bioengineering Center uses human cadavers in their crash test research. The Center's director, Albert King, wrote in 1995 that the vehicle safety improvements made possible since 1987 by the use of cadavers in research had saved nearly 8,500 lives each year, and indicated that improvements made to three-point safety belts save an average of 61 lives every year.

The New Car Assessment Program (NCAP) was put in place by the United States National Highway Traffic Safety Administration in 1979. The NCAP is a government program that evaluates vehicle safety designs and sets standards for foreign and domestic automobile companies. The agency developed a rating system and requires access to safety test results. , manufacturers are required to place an NCAP star rating on the automobile price sticker.

In 2004, The European New Car Assessment Program (Euro NCAP), started testing seat belts and whiplash safety on all test cars at the Thatcham Research Centre with crash test dummies.

Experimental
Research and development efforts are ongoing to improve the safety performance of vehicle seat belts. Some experimental designs include:
 * Criss-cross: Experimental safety belt presented in the Volvo SCC. It forms a cross-brace across the chest.
 * 3+2 Point: Experimental safety belt from Autoliv similar to the criss-cross. The 3+2 improves protection against rollovers and side impacts.
 * Four point "belt and suspenders": An experimental design from Ford where the "suspenders" are attached to the backrest, not to the frame of the car.
 * 3-point Adjustable: Experimental safety belt from GWR Safety Systems that allowed the car Hiriko, designed by MIT, to fold without compromising the safety and comfort of the occupants.

In rear seats
In 1955 (as a 1956 package), Ford offered lap-only seat belts in the rear seats as an option within the Lifeguard safety package. In 1967, Volvo started to install lap belts in the rear seats. In 1972, Volvo upgraded the rear seat belts to a three-point belt.

In crashes, unbelted rear passengers increase the risk of belted front seat occupants' death by nearly five times.

Child occupants
As with adult drivers and passengers, the advent of seat belts was accompanied by calls for their use by child occupants, including legislation requiring such use. Generally, children using adult seat belts suffer significantly lower injury risk when compared to non-buckled children.

The UK extended compulsory seat belt wearing to child passengers under the age of 14 in 1989. It was observed that this measure was accompanied by a 10% increase in fatalities and a 12% increase in injuries among the target population. In crashes, small children who wear adult seat belts can suffer "seat-belt syndrome" injuries including severed intestines, ruptured diaphragms, and spinal damage. There is also research suggesting that children in inappropriate restraints are at significantly increased risk of head injury. One of the authors of this research said, "The early graduation of kids into adult lap and shoulder belts is a leading cause of child-occupant injuries and deaths."

As a result of such findings, many jurisdictions now advocate or require child passengers to use specially designed child restraints. Such systems include separate child-sized seats with their own restraints and booster cushions for children using adult restraints. In some jurisdictions, children below a certain size are forbidden to travel in front car seats."

Automated reminders and engine start interlocks

In Europe, the U.S., and some other parts of the world, most modern cars include a seat-belt reminder light for the driver and some also include a reminder for the passenger, when present, activated by a pressure sensor under the passenger seat. Some cars will intermittently flash the reminder light and sound the chime until the driver (and sometimes the front passenger, if present) fasten their seat belts.

In 2005, in Sweden, 70% of all cars that were newly registered were equipped with seat belt reminders for the driver. Since November 2014, seat belt reminders are mandatory for the driver's seat on new cars sold in Europe.

Two specifications define the standard of seat belt reminder: UN Regulation 16, Section 8.4 and the Euro NCAP assessment protocol (Euro NCAP, 2013).

European Union seat belt reminder
In the European Union, seat belt reminders are mandatory in all new passenger cars for the driver seat. In 2014, EC Regulation 661/2009 made UN Regulation 16 applicable.

Amendment of UN Regulation 16 made seat belt reminders mandatory in
 * all front and rear seats of passenger cars and vans,
 * all front seats of buses and trucks.

This improvement applies from 1 September 2019 for new types of motor vehicles and from 1 September 2021 for all new motor vehicles.

U.S. regulation history
The Federal Motor Vehicle Safety Standard № 208 (FMVSS 208) was amended by the NHTSA to require a seat belt/starter interlock system to prevent passenger cars from being started with an unbelted front-seat occupant. This mandate applied to passenger cars built after August 1973, i.e., starting with the 1974 model year. The specifications required the system to permit the car to be started only if the belt of an occupied seat were fastened after the occupant sat down, so pre-buckling the belts would not defeat the system.

The interlock systems used logic modules complex enough to require special diagnostic computers, and were not entirely dependable—an override button was provided under the hood of equipped cars, permitting one (but only one) "free" starting attempt each time it was pressed. However, the interlock system spurred severe backlash from an American public who largely rejected seat belts. In 1974, Congress acted to prohibit NHTSA from requiring or permitting a system that prevents a vehicle from starting or operating with an unbelted occupant, or that gives an audible warning of an unfastened belt for more than 8 seconds after the ignition is turned on. This prohibition took effect on 27 October 1974, shortly after the 1975 model year began.

In response to the Congressional action, NHTSA once again amended FMVSS 208, requiring vehicles to come with a seat belt reminder system that gives an audible signal for 4 to 8 seconds and a warning light for at least 60 seconds after the ignition is turned on if the driver's seat belt is not fastened. This is called a seat belt reminder (SBR) system. In the mid-1990s, the Swedish insurance company Folksam worked with Saab and Ford to determine the requirements for the most efficient seat belt reminder. One characteristic of the optimal SBR, according to the research, is that the audible warning becomes increasingly penetrating the longer the seat belt remains unfastened.

Efficacy
In 2001, Congress directed NHSTA to study the benefits of technology meant to increase the use of seat belts. NHSTA found that seat belt usage had increased to 73% since the initial introduction of the SBR system. In 2002, Ford demonstrated that seat belts were used more in Fords with seat belt reminders than in those without: 76% and 71% respectively. In 2007, Honda conducted a similar study and found that 90% of people who drove Hondas with seat belt reminders used a seat belt, while 84% of people who drove Hondas without seat belt reminders used a seat belt.

In 2003, the Transportation Research Board Committee, chaired by two psychologists, reported that "Enhanced SBRs" (ESBRs) could save an additional 1,000 lives a year. Research by the Insurance Institute for Highway Safety found that Ford's ESBR, which provides an intermittent chime for up to five minutes if the driver is unbelted, sounding for 6 seconds then pausing for 30, increased seat belt use by 5 percentage points. Farmer and Wells found that driver fatality rates were 6% lower for vehicles with ESBR compared with otherwise-identical vehicles without.

Delayed start
Starting with the 2020 model year, some Chevrolet cars refused to shift from Park to Drive for 20 seconds if the driver is unbuckled and the car is in "teen driver" mode. A similar feature was previously available on some General Motors fleet cars.

International regulations
Several countries apply UN-ECE vehicle regulations 14 and 16:
 * UN Regulation No. 14: safety belt anchorages
 * UN Regulation No. 16:
 * Safety belts, restraint systems, child restraint systems, and ISOFIX child restraint systems for occupants of power-driven vehicles
 * Vehicles equipped with safety belts, safety belt reminders, restraint systems, child restraint systems and ISOFIX child restraint systems and i-Size child restraint systems
 * UN Regulation No. 44: restraining devices for child occupants of power-driven vehicles ("Child Restraint Systems")
 * UN Regulation No. 129: Enhanced Child Restraint Systems

Legislation
In observational studies of car crash morbidity and mortality, experiments using both crash test dummies and human cadavers indicate that wearing seat belts greatly reduces the risk of death and injury in the majority of car crashes.

This has led many countries to adopt mandatory seat belt wearing laws. It is generally accepted that, in comparing like-for-like accidents, a vehicle occupant not wearing a properly fitted seat belt has a significantly and substantially higher chance of death and serious injury. One large observation studying using U.S. data showed that the odds ratio of crash death is 0.46 with a three-point belt when compared with no belt. In another study that examined injuries presenting to the ER pre- and post-seat belt law introduction, it was found that 40% more escaped injury and 35% more escaped mild and moderate injuries.

The effects of seat belt laws are disputed by those who observe that their passage did not reduce road fatalities. There has also been concern that instead of legislating for a general protection standard for vehicle occupants, laws that required a particular technical approach would rapidly become dated as motor manufacturers would tool up for a particular standard that could not easily be changed. For example, in 1969 there were competing designs for lap and three-point seat belts, rapidly tilting seats, and airbags being developed. As countries started to mandate seat belt restraints the global auto industry invested in the tooling and standardized exclusively on seat belts, and ignored other restraint designs such as airbags for several decades

As of 2016, seat belt laws can be divided into two categories: primary and secondary. A primary seat belt law allows an officer to issue a citation for lack of seat belt use without any other citation, whereas a secondary seat belt law allows an officer to issue a seat belt citation only in the presence of a different violation. In the United States, fifteen states enforce secondary laws, while 34 states, as well as the District of Columbia, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands enforce primary seat belt laws. New Hampshire lacks either a primary or secondary seat belt law.

Risk compensation
Some have proposed that the number of deaths was influenced by the development of risk compensation, which says that drivers adjust their behavior in response to the increased sense of personal safety wearing a seat belt provides.

In one trial subjects were asked to drive go-karts around a track under various conditions. It was found that subjects who started driving unbelted drove consistently faster when subsequently belted. Similarly, a study of habitual non-seat belt wearers driving in freeway conditions found evidence that they had adapted to use by adopting higher driving speeds and closer following distances.

A 2001 analysis of U.S. crash data aimed to establish the effects of legislation on driving fatalities and found that previous estimates of seat belt effectiveness had been significantly overstated.

According to the analysis, seat belts decreased fatalities by 1.35% for each 10% increase in seat belt use. The study controlled for endogenous motivations of seat belt use, because that creates an artificial correlation between seat belt use and fatalities, leading to the conclusion that seat belts cause fatalities. For example, drivers in high-risk areas are more likely to use seat belts and are more likely to be in accidents, creating a non-causal correlation between seat belt use and mortality. After accounting for the endogeneity of seat belt usage, Cohen and Einav found no evidence that the risk compensation effect makes seat belt-wearing drivers more dangerous, a finding at variance with other research.

Increased traffic
Other statistical analyses have included adjustments for factors such as increased traffic and age, and based on these adjustments, which results in a reduction of morbidity and mortality due to seat belt use. However, Smeed's law predicts a fall in accident rate with increasing car ownership and has been demonstrated independently of seat belt legislation.

School buses
In the U.S., six states—California, Florida, Louisiana, New Jersey, New York, and Texas—require seat belts on school buses.

Pros  and cons   have been debated about the use of seat belts in school buses. School buses, which are much bigger than the average vehicle, allow for the mass transportation of students from place to place. The American School Bus Council states in a brief article: "The children are protected like eggs in an egg carton—compartmentalized, and surrounded with padding and structural integrity to secure the entire container." Although school buses are considered safe for mass transit of students, this will not guarantee that the students will be injury-free if an impact were to occur. Seat belts in buses are sometimes believed to make recovering from a roll or tip harder for passengers, as they could be easily trapped in their own safety belts.

In 2015, for the first time, NHTSA endorsed seat belts on school buses.

Motor coaches
In the European Union, all new long-distance buses and coaches must be fitted with seat belts.

Australia has required lap/sash seat belts in new coaches since 1994. These must comply with Australian Design Rule 68, which requires the seat belt, seat and seat anchorage to withstand 20g deceleration and an impact by an unrestrained occupant to the rear.

In the United States, NHTSA now requires lap-shoulder seat belts in new "over-the-road" buses (includes most coaches) starting in 2016.

Trains
The use of seat belts in trains has been investigated. Concerns about survival space intrusion in train crashes and increased injuries to unrestrained or incorrectly restrained passengers led researchers to discourage the use of seat belts in trains.

 * "It has been shown that there is no net safety benefit for passengers who choose to wear 3-point restraints on passenger-carrying rail vehicles. Generally, passengers who choose not to wear restraints in a vehicle modified to accept 3-point restraints receive marginally more severe injuries."

Airplanes

All aerobatic aircraft and gliders (sailplanes) are fitted with four or five-point harnesses, as are many types of light aircraft and many types of military aircraft. The seat belts in these aircraft have the dual function of crash protection and keeping the pilot(s) and crew in their seat(s) during turbulence and aerobatic maneuvers. Passenger aircraft are fitted with lap belts. Unlike road vehicles, passenger aircraft seat belts are not primarily designed for crash protection. Their main purpose is to keep passengers in their seats during events such as turbulence. Many civil aviation authorities require a "fasten seat belt" sign in passenger aircraft that can be activated by a pilot during takeoff, turbulence, and landing. The International Civil Aviation Organization recommends the use of child restraints. Some airline authorities, including the UK Civil Aviation Authority (CAA), permit the use of airline infant lap belts (sometimes known as an infant loop or belly belt) to secure an infant under age two sitting on an adult's lap.

title: Seat belt


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Rolf Singer

Rolf Singer (June 23, 1906 – January 18, 1994) was a German mycologist and taxonomist of gilled mushrooms (agarics).

He wrote the book "The Agaricales in Modern Taxonomy". He fled to various countries during the Nazi period, pursuing mycology in the Soviet Union, Argentina, and finally the United States, as mycologist at the Field Museum in Chicago.

Career
After receiving his Ph.D. at the University of Vienna in 1931 he worked in Munich. By 1933, however, Singer left Germany for Vienna due to the political deterioration in Germany. There he met his wife, Martha Singer. From Vienna, Singer and his wife went to Barcelona, Spain, where Singer was appointed assistant professor at the Autonomous University of Barcelona. Persecution by the Spanish authorities on behalf of the German government forced Singer to leave Spain for France in 1934. After a fellowship at the Museum d'Histoire Naturelle in Paris, Singer again moved, this time to Leningrad, where he was senior scientific expert at the Botanical Garden of the Academy of Sciences of the USSR. During his time at the academy, Singer made many expeditions to Siberia, the Altai Mountains, and Karelia. In 1941, Singer emigrated to the United States. He was offered a position at Harvard University's Farlow Herbarium as a research associate, then as Assistant Curator, then as acting Curator following the death of Dr. David Linder. He spent a total of seven years at the Farlow. During this time, Singer also received a Guggenheim Fellowship for studies in Florida, and taught at the Mountain Lake Biological Station of the University of Virginia.

In 1948, Singer left Harvard to become professor at the Universidad Nacional de Tucuman in Argentina. Later, in 1961, Singer became professor at the Universidad de Buenos Aires. During his time in South America, Singer, his wife, and his daughter Heidi collected extensively. Singer's last faculty appointment was at the University of Illinois at Chicago, from 1968 to 1977.

Singer was an author (or co-author) of new fungal species, having formally described 2260 in his career. He was also a prolific writer, with more than 400 publications to his name.

Honours
He has been honoured in the naming of several taxa of fungi. Including; Singeriella in 1959 (in Vizellaceae family), Singera  1960 (Vermiculariopsiellaceae family), Mesosingeria  (Fossil, order Cycadales), Singeromyces  (in the family Boletaceae), Singerina (in the family Agaricaceae), and lastly, Singerocomus  (Boletaceae family).

Other sources

 * Singer, Rolf. "Curriculum Vitae"
 * Singer, Rolf. "Curriculum Vitae"
 * Singer, Rolf. "Curriculum Vitae"

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Rolf Singer


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Hypha

A hypha (: hyphae) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.

Structure
A hypha consists of one or more cells surrounded by a tubular cell wall. In most fungi, hyphae are divided into cells by internal cross-walls called "septa" (singular septum). Septa are usually perforated by pores large enough for ribosomes, mitochondria, and sometimes nuclei to flow between cells. The major structural polymer in fungal cell walls is typically chitin, in contrast to plants and oomycetes that have cellulosic cell walls. Some fungi have aseptate hyphae, meaning their hyphae are not partitioned by septa.

Hyphae have an average diameter of 4–6 μm.

Growth
Hyphae grow at their tips. During tip growth, cell walls are extended by the external assembly and polymerization of cell wall components, and the internal production of new cell membrane. The Spitzenkörper is an intracellular organelle associated with tip growth. It is composed of an aggregation of membrane-bound vesicles containing cell wall components. The Spitzenkörper is part of the endomembrane system of fungi, holding and releasing vesicles it receives from the Golgi apparatus. These vesicles travel to the cell membrane via the cytoskeleton and release their contents (including various cysteine-rich proteins including cerato-platanins and hydrophobins) outside the cell by the process of exocytosis, where they can then be transported to where they are needed. Vesicle membranes contribute to growth of the cell membrane while their contents form new cell wall. The Spitzenkörper moves along the apex of the hyphal strand and generates apical growth and branching; the apical growth rate of the hyphal strand parallels and is regulated by the movement of the Spitzenkörper.

As a hypha extends, septa may be formed behind the growing tip to partition each hypha into individual cells. Hyphae can branch through the bifurcation of a growing tip, or by the emergence of a new tip from an established hypha.

Behavior
The direction of hyphal growth can be controlled by environmental stimuli, such as the application of an electric field. Hyphae can also sense reproductive units from some distance, and grow towards them. Hyphae can weave through a permeable surface to penetrate it.

Modifications
Hyphae may be modified in many different ways to serve specific functions. Some parasitic fungi form haustoria that function in absorption within the host cells. The arbuscules of mutualistic mycorrhizal fungi serve a similar function in nutrient exchange, so are important in assisting nutrient and water absorption by plants. Ectomycorrhizal extramatrical mycelium greatly increases the soil area available for exploitation by plant hosts by funneling water and nutrients to ectomycorrhizas, complex fungal organs on the tips of plant roots. Hyphae are found enveloping the gonidia in lichens, making up a large part of their structure. In nematode-trapping fungi, hyphae may be modified into trapping structures such as constricting rings and adhesive nets. Mycelial cords can be formed to transfer nutrients over larger distances. Bulk fungal tissues, cords, and membranes, such as those of mushrooms and lichens, are mainly composed of felted and often anastomosed hyphae.

Classification based on cell division

 * Septate (with septa)
 * Aspergillus and many other species have septate hyphae.
 * Aseptate (non-septate) or coenocytic (without septa)
 * Non-septate hyphae are associated with Mucor, some zygomycetes, and other fungi.
 * Pseudohyphae are distinguished from true hyphae by their method of growth, relative frailty and lack of cytoplasmic connection between the cells.
 * Yeasts form pseudohyphae. They are the result of a sort of incomplete budding where the cells elongate but remain attached after division. Some yeasts can also form true septate hyphae.

Classification based on cell wall and overall form
Characteristics of hyphae can be important in fungal classification. In basidiomycete taxonomy, hyphae that comprise the fruiting body can be identified as generative, skeletal, or binding hyphae.
 * Generative hyphae are relatively undifferentiated and can develop reproductive structures. They are typically thin-walled, occasionally developing slightly thickened walls, usually have frequent septa, and may or may not have clamp connections. They may be embedded in mucilage or gelatinized materials.
 * Skeletal hyphae are of two basic types. The classical form is thick-walled and very long in comparison to the frequently septate generative hyphae, which are unbranched or rarely branched, with little cell content.  They have few septa and lack clamp connections. Fusiform skeletal hyphae are the second form of skeletal hyphae. Unlike typical skeletal hyphae these are swollen centrally and often exceedingly broad, hence giving the hypha a fusiform shape.
 * Binding hyphae are thick-walled and frequent branched. Often they resemble deer antlers or defoliated trees because of the many tapering branches.

Based on the generative, skeletal and binding hyphal types, in 1932 E. J. H. Corner applied the terms monomitic, dimitic, and trimitic to hyphal systems, in order to improve the classification of polypores. Fungi that form fusiform skeletal hyphae bound by generative hyphae are said to have sarcodimitic hyphal systems. A few fungi form fusiform skeletal hyphae, generative hyphae, and binding hyphae, and these are said to have sarcotrimitic hyphal systems. These terms were introduced as a later refinement by E. J. H. Corner in 1966.
 * Every fungus must contain generative hyphae. A fungus which only contains this type, as do fleshy mushrooms such as agarics, is referred to as monomitic.
 * If a fungus contains the obligate generative hyphae (as mentioned in the last point, "every fungus must contain generative hyphae") and just one of the other two types (either skeletal or binding hyphae), it is called dimitic. In fact dimitic fungi almost always contain generative and skeletal hyphae; there is one exceptional genus, Laetiporus that includes only generative and binding hyphae.
 * Skeletal and binding hyphae give leathery and woody fungi such as polypores their tough consistency. If a fungus contains all three types (example: Trametes), it is called trimitic.

Classification based on refractive appearance
Hyphae are described as "gloeoplerous" ("gloeohyphae") if their high refractive index gives them an oily or granular appearance under the microscope. These cells may be yellowish or clear (hyaline). They can sometimes selectively be coloured by sulphovanillin or other reagents. The specialized cells termed cystidia can also be gloeoplerous.

Classification based on growth location
Hyphae might be categorized as 'vegetative' or 'aerial.' Aerial hyphae of fungi produce asexual reproductive spores.

title: Hypha


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Jurist

A jurist is a person with expert knowledge of law; someone who analyzes and comments on law. This person is usually a specialist legal scholar, mostly (but not always) with a formal education in law (a law degree) and often a legal practitioner.

In the United Kingdom the term "jurist" is mostly used for legal academics, while in the United States the term may also be applied to a judge. With reference to Roman law, a "jurist" (in English) is a jurisconsult (iurisconsultus).

The English term jurist is to be distinguished from similar terms in other European languages, where it may be synonymous with legal professional, meaning anyone with a professional law degree that qualifies for admission to the legal profession, including such positions as judge or attorney. In Germany, Scandinavia and a number of other countries jurist denotes someone with a professional law degree, and it may be a protected title, for example in Norway. Thus the term can be applied to attorneys, judges and academics, provided that they hold a qualifying professional law degree. In Germany – the term "full jurist" is sometimes used informally to denote someone who has completed the two state examinations in law that qualify for practising law, to distinguish from someone who may have only the first state examination or some other form of legal qualification that does not qualify for practising law.

Notable jurists
Some notable historical jurists include:

• Ur-Nammu

• Lycurgus of Sparta

• Solon of Athens

• B. R. Ambedkar

• Ulpian and Gaius

• Muhammad Averroes

• Thomas Aquinas

• Alberico Gentili

• Francis Bacon

• William Blackstone

• Cesare Beccaria

• Jeremy Bentham

• Amina, bint al-Hajj ʿAbd al-Latif

• John Stuart Mill

• John Marshall

• Muhammad Iqbal

• Felix Frankfurter

• Oliver Wendell Holmes Jr.

• Hans Kelsen

• Pontes de Miranda

title: Jurist


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Mutualism (biology)

Mutualism describes the ecological interaction between two or more species where each species has a net benefit. Mutualism is a common type of ecological interaction. Prominent examples are:
 * the nutrient exchange between vascular plants and mycorrhizal fungi,
 * the fertilization of flowering plants by pollinators,
 * the ways plants use fruits and edible seeds to encourage animal aid in seed dispersal, and
 * the way corals become photosynthetic with the help of the microorganism zooxanthellae.

Mutualism can be contrasted with interspecific competition, in which each species experiences reduced fitness, and exploitation, and with parasitism, in which one species benefits at the expense of the other. However, mutualism may evolve from interactions that began with imbalanced benefits, such as parasitism.

The term mutualism was introduced by Pierre-Joseph van Beneden in his 1876 book Animal Parasites and Messmates to mean "mutual aid among species".

Mutualism is often conflated with two other types of ecological phenomena: cooperation and symbiosis. Cooperation most commonly refers to increases in fitness through within-species (intraspecific) interactions, although it has been used (especially in the past) to refer to mutualistic interactions, and it is sometimes used to refer to mutualistic interactions that are not obligate. Symbiosis involves two species living in close physical contact over a long period of their existence and may be mutualistic, parasitic, or commensal, so symbiotic relationships are not always mutualistic, and mutualistic interactions are not always symbiotic. Despite a different definition between mutualistic interactions and symbiosis, mutualistic and symbiosis have been largely used interchangeably in the past, and confusion on their use has persisted.

Mutualism plays a key part in ecology and evolution. For example, mutualistic interactions are vital for terrestrial ecosystem function as:
 * about 80% of land plants species rely on mycorrhizal relationships with fungi to provide them with inorganic compounds and trace elements.
 * estimates of tropical rainforest plants with seed dispersal mutualisms with animals range at least from 70% to 93.5%. In addition, mutualism is thought to have driven the evolution of much of the biological diversity we see, such as flower forms (important for pollination mutualisms) and co-evolution between groups of species.

A prominent example of pollination mutualism is with bees and flowering plants. Bees use these plants as their food source with pollen and nectar. In turn, they transfer pollen to other nearby flowers, inadvertently allowing for cross-pollination. Cross-pollination has become essential in plant reproduction and fruit/seed production. The bees get their nutrients from the plants, and allow for successful fertilization of plants, demonstrating a mutualistic relationship between two seemingly-unlike species.

Mutualism has also been linked to major evolutionary events, such as the evolution of the eukaryotic cell (symbiogenesis) and the colonization of land by plants in association with mycorrhizal fungi.

Resource-resource relationships
Mutualistic relationships can be thought of as a form of "biological barter" in mycorrhizal associations between plant roots and fungi, with the plant providing carbohydrates to the fungus in return for primarily phosphate but also nitrogenous compounds. Other examples include rhizobia bacteria that fix nitrogen for leguminous plants (family Fabaceae) in return for energy-containing carbohydrates. Metabolite exchange between multiple mutualistic species of bacteria has also been observed in a process known as cross-feeding.

Service-resource relationships

Service-resource relationships are common. Three important types are pollination, cleaning symbiosis, and zoochory.

In pollination, a plant trades food resources in the form of nectar or pollen for the service of pollen dispersal. However, daciniphilous Bulbophyllum orchid species trade sex pheromone precursor or booster components via floral synomones/attractants in a true mutualistic interactions with males of Dacini fruit flies (Diptera: Tephritidae: Dacinae).

Phagophiles feed (resource) on ectoparasites, thereby providing anti-pest service, as in cleaning symbiosis. Elacatinus and Gobiosoma, genera of gobies, feed on ectoparasites of their clients while cleaning them.

Zoochory is the dispersal of the seeds of plants by animals. This is similar to pollination in that the plant produces food resources (for example, fleshy fruit, overabundance of seeds) for animals that disperse the seeds (service). Plants may advertise these resources using colour and a variety of other fruit characteristics, e.g., scent. Fruit of the aardvark cucumber (Cucumis humifructus) is buried so deeply that the plant is solely reliant upon the aardvark's keen sense of smell to detect its ripened fruit, extract, consume and then scatter its seeds; C. humifructus's geographical range is thus restricted to that of the aardvark's.

Another type is ant protection of aphids, where the aphids trade sugar-rich honeydew (a by-product of their mode of feeding on plant sap) in return for defense against predators such as ladybugs.

Service-service relationships

Strict service-service interactions are very rare, for reasons that are far from clear. One example is the relationship between sea anemones and anemone fish in the family Pomacentridae: the anemones provide the fish with protection from predators (which cannot tolerate the stings of the anemone's tentacles) and the fish defend the anemones against butterflyfish (family Chaetodontidae), which eat anemones. However, in common with many mutualisms, there is more than one aspect to it: in the anemonefish-anemone mutualism, waste ammonia from the fish feeds the symbiotic algae that are found in the anemone's tentacles. Therefore, what appears to be a service-service mutualism in fact has a service-resource component. A second example is that of the relationship between some ants in the genus Pseudomyrmex and trees in the genus Acacia, such as the whistling thorn and bullhorn acacia. The ants nest inside the plant's thorns. In exchange for shelter, the ants protect acacias from attack by herbivores (which they frequently eat when those are small enough, introducing a resource component to this service-service relationship) and competition from other plants by trimming back vegetation that would shade the acacia. In addition, another service-resource component is present, as the ants regularly feed on lipid-rich food-bodies called Beltian bodies that are on the Acacia plant.

In the neotropics, the ant Myrmelachista schumanni makes its nest in special cavities in Duroia hirsute. Plants in the vicinity that belong to other species are killed with formic acid. This selective gardening can be so aggressive that small areas of the rainforest are dominated by Duroia hirsute. These peculiar patches are known by local people as "devil's gardens".

In some of these relationships, the cost of the ant's protection can be quite expensive. Cordia sp. trees in the Amazonian rainforest have a kind of partnership with Allomerus sp. ants, which make their nests in modified leaves. To increase the amount of living space available, the ants will destroy the tree's flower buds. The flowers die and leaves develop instead, providing the ants with more dwellings. Another type of Allomerus sp. ant lives with the Hirtella sp. tree in the same forests, but in this relationship, the tree has turned the tables on the ants. When the tree is ready to produce flowers, the ant abodes on certain branches begin to wither and shrink, forcing the occupants to flee, leaving the tree's flowers to develop free from ant attack.

The term "species group" can be used to describe the manner in which individual organisms group together. In this non-taxonomic context one can refer to "same-species groups" and "mixed-species groups." While same-species groups are the norm, examples of mixed-species groups abound. For example, zebra (Equus burchelli) and wildebeest (Connochaetes taurinus) can remain in association during periods of long distance migration across the Serengeti as a strategy for thwarting predators. Cercopithecus mitis and Cercopithecus ascanius, species of monkey in the Kakamega Forest of Kenya, can stay in close proximity and travel along exactly the same routes through the forest for periods of up to 12 hours. These mixed-species groups cannot be explained by the coincidence of sharing the same habitat. Rather, they are created by the active behavioural choice of at least one of the species in question.

Mathematical modeling
Mathematical treatments of mutualisms, like the study of mutualisms in general, have lagged behind those for predation, or predator-prey, consumer-resource, interactions. In models of mutualisms, the terms "type I" and "type II" functional responses refer to the linear and saturating relationships, respectively, between the benefit provided to an individual of species 1 (dependent variable) and the density of species 2 (independent variable).

Type I functional response
One of the simplest frameworks for modeling species interactions is the Lotka–Volterra equations. In this model, the changes in population densities of the two mutualists are quantified as:

\begin{align} \frac{dN_1}{dt} &=r_1 N_1 - \alpha_{11} N_1^2 + \beta _{12}N_1N_2 \\[8pt] \frac{dN_2}{dt} &=r_2 N_2 - \alpha_{22} N_2^2 + \beta _{21}N_1N_2 \end{align} $$

where Mutualism is in essence the logistic growth equation modified for mutualistic interaction. The mutualistic interaction term represents the increase in population growth of one species as a result of the presence of greater numbers of another species. As the mutualistic interactive term β is always positive, this simple model may lead to unrealistic unbounded growth. So it may be more realistic to include a further term in the formula, representing a saturation mechanism, to avoid this occurring.
 * $$N_i$$ = the population density of species i.
 * $$r_i$$ = the intrinsic growth rate of the population of species i.
 * $$\alpha _{ii}$$ = the negative effect of within-species crowding on species i.
 * $$\beta _{ij}$$ = the beneficial effect of the density of species j on species i.

Type II functional response
In 1989, David Hamilton Wright modified the above Lotka–Volterra equations by adding a new term, βM/K, to represent a mutualistic relationship. Wright also considered the concept of saturation, which means that with higher densities, there is a decrease in the benefits of further increases of the mutualist population. Without saturation, depending on the size of parameter α, species densities would increase indefinitely. Because that is not possible due to environmental constraints and carrying capacity, a model that includes saturation would be more accurate. Wright's mathematical theory is based on the premise of a simple two-species mutualism model in which the benefits of mutualism become saturated due to limits posed by handling time. Wright defines handling time as the time needed to process a food item, from the initial interaction to the start of a search for new food items and assumes that processing of food and searching for food are mutually exclusive. Mutualists that display foraging behavior are exposed to the restrictions on handling time. Mutualism can be associated with symbiosis.

 * Handling time interactions

In 1959, C. S. Holling performed his classic disc experiment that assumed that
 * 1) the number of food items captured is proportional to the allotted searching time; and
 * 2) that there is a handling time variable that exists separately from the notion of search time. He then developed an equation for the Type II functional response, which showed that the feeding rate is equivalent to

 * $$\cfrac{ax}{1+axT_H}$$

where
 * a = the instantaneous discovery rate
 * x = food item density
 * TH = handling time

The equation that incorporates Type II functional response and mutualism is:

\frac{dN}{dt}=N\left[r(1-cN)+\cfrac{baM}{1+aT_H M}\right] $$

where
 * N and M = densities of the two mutualists
 * r = intrinsic rate of increase of N
 * c = coefficient measuring negative intraspecific interaction. This is equivalent to inverse of the carrying capacity, 1/K, of N, in the logistic equation.
 * a = instantaneous discovery rate
 * b = coefficient converting encounters with M to new units of N

or, equivalently,

\frac{dN}{dt}=N[r(1-cN)+\beta M/(X+M)] $$

where
 * X = 1/aTH
 * β = b/TH

This model is most effectively applied to free-living species that encounter a number of individuals of the mutualist part in the course of their existences. Wright notes that models of biological mutualism tend to be similar qualitatively, in that the featured isoclines generally have a positive decreasing slope, and by and large similar isocline diagrams. Mutualistic interactions are best visualized as positively sloped isoclines, which can be explained by the fact that the saturation of benefits accorded to mutualism or restrictions posed by outside factors contribute to a decreasing slope.

The type II functional response is visualized as the graph of $$\cfrac{baM}{1+aT_H M}$$ vs. M.

Structure of networks
Mutualistic networks made up out of the interaction between plants and pollinators were found to have a similar structure in very different ecosystems on different continents, consisting of entirely different species. The structure of these mutualistic networks may have large consequences for the way in which pollinator communities respond to increasingly harsh conditions and on the community carrying capacity.

Mathematical models that examine the consequences of this network structure for the stability of pollinator communities suggest that the specific way in which plant-pollinator networks are organized minimizes competition between pollinators, reduce the spread of indirect effects and thus enhance ecosystem stability and may even lead to strong indirect facilitation between pollinators when conditions are harsh. This means that pollinator species together can survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass a critical point. This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions.

Such a community-wide collapse, involving many pollinator species, can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover could be substantially larger than the improvement needed to return to conditions at which the pollinator community collapsed.

Humans

Humans are involved in mutualisms with other species: their gut flora is essential for efficient digestion. Infestations of head lice might have been beneficial for humans by fostering an immune response that helps to reduce the threat of body louse borne lethal diseases.

Some relationships between humans and domesticated animals and plants are to different degrees mutualistic. For example, agricultural varieties of maize provide food for humans and are unable to reproduce without human intervention because the leafy sheath does not fall open, and the seedhead (the "corn on the cob") does not shatter to scatter the seeds naturally.

In traditional agriculture, some plants have mutualist as companion plants, providing each other with shelter, soil fertility and/or natural pest control. For example, beans may grow up cornstalks as a trellis, while fixing nitrogen in the soil for the corn, a phenomenon that is used in Three Sisters farming.

One researcher has proposed that the key advantage Homo sapiens had over Neanderthals in competing over similar habitats was the former's mutualism with dogs.

Intestinal microbiota
The microbiota in the human intestine coevolved with the human species, and this relationship is considered to be a mutualism that is beneficial both to the human host and the bacteria in the gut population. The mucous layer of the intestine contains commensal bacteria that produce bacteriocins, modify the pH of the intestinal contents, and compete for nutrition to inhibit colonization by pathogens. The gut microbiota, containing trillions of microorganisms, possesses the metabolic capacity to produce and regulate multiple compounds that reach the circulation and act to influence the function of distal organs and systems. Breakdown of the protective mucosal barrier of the gut can contribute to the development of colon cancer.

Evolution by type
Every generation of every organism needs nutrients and similar nutrients  more than they need particular defensive characteristics, as the fitness benefit of these vary heavily especially by environment. This may be the reason that hosts are more likely to evolve to become dependent on vertically transmitted bacterial mutualists which provide nutrients than those providing defensive benefits. This pattern is generalized beyond bacteria by Yamada et al. 2015's demonstration that undernourished Drosophila are heavily dependent on their fungal symbiont Issatchenkia orientalis for amino acids.

Mutualism breakdown
Mutualisms are not static, and can be lost by evolution. Sachs and Simms (2006) suggest that this can occur via four main pathways:
 * 1) One mutualist shifts to parasitism, and no longer benefits its partner, such as headlice
 * 2) One partner abandons the mutualism and lives autonomously
 * 3) One partner may go extinct
 * 4) A partner may be switched to another species

There are many examples of mutualism breakdown. For example, plant lineages inhabiting nutrient-rich environments have evolutionarily abandoned mycorrhizal mutualisms many times independently. Evolutionarily, headlice may have been mutualistic as they allow for early immunity to various body-louse borne disease; however, as these diseases became eradicated, the relationship has become less mutualistic and more parasitic.

Measuring and defining mutualism
Measuring the exact fitness benefit to the individuals in a mutualistic relationship is not always straightforward, particularly when the individuals can receive benefits from a variety of species, for example most plant-pollinator mutualisms. It is therefore common to categorise mutualisms according to the closeness of the association, using terms such as obligate and facultative. Defining "closeness", however, is also problematic. It can refer to mutual dependency (the species cannot live without one another) or the biological intimacy of the relationship in relation to physical closeness (e.g., one species living within the tissues of the other species).

Further references

 * Bronstein JL. 2001. The costs of mutualism. American Zoologist 41 (4): 825-839 S
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Bronstein JL. 2001. The costs of mutualism. American Zoologist 41 (4): 825-839 S
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Ollerton, J. 2006. "Biological Barter": Patterns of Specialization Compared across Different Mutualisms. pp. 411–435 in: Waser, N.M. & Ollerton, J. (Eds) Plant-Pollinator Interactions: From Specialization to Generalization. University of Chicago Press. ISBN 978-0-226-87400-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5
 * Thompson, J. N. 2005. The Geographic Mosaic of Coevolution. University of Chicago Press. ISBN 978-0-226-79762-5

title: Mutualism (biology)


text:
German Workers' Party

The German Workers' Party (Deutsche Arbeiterpartei, DAP) was a short-lived far-right political party established in Weimar Germany after World War I. It only lasted from 5 January 1919 until 24 February 1920. The DAP was the precursor of the Nazi Party, which was officially known as the National Socialist German Workers' Party (Nationalsozialistische Deutsche Arbeiterpartei, NSDAP).

Origins
On 5 January 1919, the German Workers' Party (DAP) was founded in Munich in the hotel Fürstenfelder Hof by Anton Drexler, along with Dietrich Eckart, Gottfried Feder and Karl Harrer. It developed out of the Freien Arbeiterausschuss für einen guten Frieden (Free Workers' Committee for a Good Peace) league, a branch of which Drexler had founded in 1918. Thereafter in 1918, Harrer (a journalist and member of the Thule Society), convinced Drexler and several others to form the Politischer Arbeiterzirkel (Political Workers' Circle). The members met periodically for discussions with themes of nationalism and antisemitism. Drexler was encouraged to form the DAP in December 1918 by his mentor, Dr. Paul Tafel. Tafel was a leader of the Alldeutscher Verband (Pan-Germanist Union), a director of the Maschinenfabrik Augsburg-Nürnberg and a member of the Thule Society. Drexler's wish was for a political party which was both in touch with the masses and nationalist. When the DAP was founded in January 1919, Drexler was elected chairman and Harrer was made Reich Chairman, an honorary title. On 17 May, only ten members were present at the meeting, and a later meeting in August only noted 38 members attending. The members were mainly Drexler's colleagues from the Munich railway yards.

Adolf Hitler's membership
After World War I ended, Adolf Hitler returned to Munich. Having no formal education or career prospects, he tried to remain in the army for as long as possible. In July 1919, he was appointed Verbindungsmann (intelligence agent) of an Aufklärungskommando (reconnaissance commando) of the Reichswehr to influence other soldiers and to investigate the DAP. While Hitler was initially unimpressed by the meetings and found them disorganised, he enjoyed the discussion that took place. During these investigations, Hitler became attracted to founder Anton Drexler's anti-Semitic, nationalist, anti-capitalist, and anti-Marxist ideas. While attending a party meeting at the Sterneckerbräu beer hall on 12 September 1919, Hitler became involved in a heated political argument with a visitor, Professor Baumann, who questioned the soundness of Gottfried Feder's arguments in support of Bavarian separatism and against capitalism. In vehemently attacking the man's arguments, he made an impression on the other party members with his oratory skills and, according to Hitler, Baumann left the hall acknowledging unequivocal defeat. Impressed with Hitler's oratory skills, Drexler encouraged him to join. On the orders of his army superiors, Hitler applied to join the party. Although Hitler initially wanted to form his own party, he claimed to have been convinced to join the DAP because it was small and he could eventually become its leader. He consequently encouraged the organisation to become less of a debating society, which it had been previously, and more of an active political party.

In less than a week, Hitler received a postcard stating he had officially been accepted as a member and he should come to a committee meeting to discuss it. Hitler attended the committee meeting held at the run-down Altes Rosenbad beer-house. Normally, enlisted army personnel were not allowed to join political parties. In this case, Hitler had Captain Karl Mayr's permission to join the DAP. Further, Hitler was allowed to stay in the army and receive his weekly pay of 20 gold marks. Unlike many other members of the organisation, this continued employment provided him with enough money to dedicate himself more fully to the DAP. At the time when Hitler joined the party, there were no membership numbers or cards. It was in January 1920 when a numeration was issued for the first time and listed in alphabetical order Hitler received the number 555. In reality, he had been the 55th member, but the counting started at the number 501 in order to make the party appear larger. In his work Mein Kampf, Hitler later claimed to be the seventh party member, but he was in fact the seventh executive member of the party's central committee.

During 1919, the DAP set out an explicit program of being nationalistic, anti-Semitic, and anti-Marxist. Unlike other similar nationalist parties at the time, the DAP aimed its rhetoric towards working class Germans, hoping to cross class boundaries and recruit them. However, Hitler explicitly rejected the Marxist idea of dictatorship of the proletariat, and instead attempted to appeal to the working class to create a "volksgemeinshaft" (people's community), where German identity took precedence over class, religion, or other ideas.

After giving his first speech for the DAP on 16 October at the Hofbräukeller, Hitler quickly became the party's most active orator. Hitler's considerable oratory and propaganda skills were appreciated by the party leadership as crowds began to flock to hear his speeches during 1919–1920. Such was the popularity of Hitler's speaking skills, the party began charging an entry fee for visitors to hear his speeches. With the support of Drexler, Hitler became chief of propaganda for the party in early 1920. Hitler preferred that role as he saw himself as the drummer for a national cause. He saw propaganda as the way to bring nationalism to the public.

From DAP to NSDAP
The small number of party members were quickly won over to Hitler's political beliefs. He organized their biggest meeting yet of 2,000 people on 24 February 1920 in the Staatliches Hofbräuhaus in München (a beer hall in Munich). Further in an attempt to make the party more broadly appealing to larger segments of the population, the DAP was renamed the National Socialist German Workers' Party (NSDAP) on 24 February. Such was the significance of Hitler's particular move in publicity that Harrer resigned from the party in disagreement. The new name was borrowed from a different Austrian party active at the time (the Deutsche Nationalsozialistische Arbeiterpartei, i.e. the German National Socialist Workers' Party), although Hitler earlier suggested the party to be renamed the Social Revolutionary Party in order to distance the party from association with socialism. It was Rudolf Jung who persuaded Hitler to adopt the NSDAP name. The name was intended to draw upon both left-wing and right-wing ideals, with "Socialist" and "Workers'" appealing to the left, and "National" and "German" appealing to the right.

Membership
Early members of the party included:
 * Anton Drexler
 * Dietrich Eckart
 * Gottfried Feder
 * Karl Harrer
 * Hermann Esser
 * Ernst Boepple
 * Hans Frank
 * Adolf Hitler
 * Rudolf Hess
 * Ernst Röhm
 * Alfred Rosenberg
 * Rudolf Jung

title: German Workers' Party