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Cursus honorum

The, or more colloquially 'ladder of offices'; ) was the sequential order of public offices held by aspiring politicians in the Roman Republic and the early Roman Empire. It was designed for men of senatorial rank. The cursus honorum comprised a mixture of military and political administration posts; the ultimate prize for winning election to each "rung" in the sequence was to become one of the two consuls in a given year.

These rules were altered and flagrantly ignored in the course of the last century of the Republic. For example, Gaius Marius held consulships for five years in a row between 104 BC and 100 BC. He was consul seven times in all, also serving in 107 and 86. Officially presented as opportunities for public service, the offices often became mere opportunities for self-aggrandizement. The constitutional reforms of Sulla between 82 and 79 BC required a ten-year interval before holding the same office again for another term.

To have held each office at the youngest possible age (suo anno, 'in his year') was considered a great political success. For instance, to miss out on a praetorship at 39 meant that one could not become consul at 42. Cicero expressed extreme pride not only in being a novus homo ('new man'; comparable to a "self-made man") who became consul even though none of his ancestors had ever served as a consul, but also in having become consul "in his year".

Military service
Prior to entering political life and the cursus honorum, a young man of senatorial rank was expected to serve around ten years of military duty. The years of service were intended to be mandatory in order to qualify for political office.

Advancement and honors would improve his political prospects, and a successful military career might culminate in the office of military tribune, to which 24 men were elected by the Tribal Assembly each year. The rank of military tribune is sometimes described as the first office of the cursus honorum.

Quaestor
The first official post was that of quaestor. Ever since the reforms of Sulla, candidates had to be at least 30 years old to hold the office. From the time of Augustus onwards, twenty quaestors served in the financial administration at Rome or as second-in-command to a governor in the provinces. They could also serve as the paymaster for a legion.

Aedile
At 36 years of age, a promagistrate could stand for election to one of the aediles (pronounced, from aedes, "temple edifice") positions. Of these aediles, two were plebeian and two were patrician, with the patrician aediles called curule aediles. The plebeian aediles were elected by the Plebeian Council and the curule aediles were either elected by the Tribal Assembly or appointed by the reigning consul. The aediles had administrative responsibilities in Rome. They had to take care of the temples (whence their title, from the Latin aedes, "temple"), organize games, and be responsible for the maintenance of the public buildings in Rome. Moreover, they took charge of Rome's water and food supplies; in their capacity as market superintendents, they served sometimes as judges in mercantile affairs.

The aedile was the supervisor of public works; the words "edifice" and "edification" stem from the same root. He oversaw the public works, temples and markets. Therefore, the aediles would have been in some cooperation with the current censors, who had similar or related duties. Also, they oversaw the organization of festivals and games (ludi), which made this a very sought-after office for a career minded politician of the late Republic, as it was a good means of gaining popularity by staging spectacles. Curule aediles were added at a later date in the 4th century BC; their duties do not differ substantially from plebeian aediles. However, unlike plebeian aediles, curule aediles were allowed certain symbols of rank—the sella curulis or curule chair, for example—and only patricians could stand for election to curule aedile. This later changed, and both plebeians and patricians could stand for curule aedileship.

The elections for curule aedile were at first alternated between patricians and plebeians, until late in the 2nd century BC, when the practice was abandoned and both classes became free to run during all years.

While part of the cursus honorum, this step was optional and not required to hold future offices. Though the office was usually held after the quaestorship and before the praetorship, there are some cases with former praetors serving as aediles.

Praetor
After serving either as quaestor or as aedile, a man of 39 years could run for praetor. During the reign of Augustus this requirement was lowered to 30, at the request of Gaius Maecenas. The number of praetors elected varied through history, generally increasing with time. During the republic, six or eight were generally elected each year to serve judicial functions throughout Rome and other governmental responsibilities. In the absence of the consuls, a praetor would be given command of the garrison in Rome or in Italy. Also, a praetor could exercise the functions of the consuls throughout Rome, but their main function was that of a judge. They would preside over trials involving criminal acts, grant court orders and validate "illegal" acts as acts of administering justice. A praetor was escorted by six lictors, and wielded imperium. After a term as praetor, the magistrate could serve as a provincial governor with the title of propraetor, wielding propraetor imperium, commanding the province's legions, and possessing ultimate authority within his province(s).

Two of the praetors were more prestigious than the others. The first was the Praetor Peregrinus, who was the chief judge in trials involving one or more foreigners. The other was the Praetor Urbanus, the chief judicial office in Rome. He had the power to overturn any verdict by any other courts, and served as judge in cases involving criminal charges against provincial governors. The Praetor Urbanus was not allowed to leave the city for more than ten days. If one of these two praetors was absent from Rome, the other would perform the duties of both.

Consul
The office of consul was the most prestigious of all of the offices on the cursus honorum, and represented the summit of a successful career. The minimum age was 42. Years were identified by the names of the two consuls elected for a particular year; for instance, M. Messalla et M. Pisone consulibus, "in the consulship of Messalla and Piso",  dates an event to 61 BC. Consuls were responsible for the city's political agenda, commanded large-scale armies and controlled important provinces. The consuls served for only a year (a restriction intended to limit the amassing of power by individuals) and could only rule when they agreed, because each consul could veto the other's decision.

The consuls would alternate monthly as the chairman of the Senate. They also were the supreme commanders in the Roman army, with each being granted two legions during their consular year. Consuls also exercised the highest juridical power in the Republic, being the only office with the power to override the decisions of the Praetor Urbanus. Only laws and the decrees of the Senate or the People's assembly limited their powers, and only the veto of a fellow consul or a tribune of the plebs could supersede their decisions.

A consul was escorted by twelve lictors, held imperium and wore the toga praetexta. Because the consul was the highest executive office within the Republic, they had the power to veto any action or proposal by any other magistrate, save that of the Tribune of the Plebs. After a consulship, a consul was assigned one of the more important provinces and acted as the governor in the same way that a propraetor did, only owning proconsular imperium. A second consulship could only be attempted after an interval of 10 years to prevent one man holding too much power.

Governor
Although not part of the cursus honorum, upon completing a term as either praetor or consul, an officer was required to serve a term as propraetor and proconsul, respectively, in one of Rome's many provinces. These propraetors and proconsuls held near autocratic authority within their selected province or provinces. Because each governor held equal imperium to the equivalent magistrate, they were escorted by the same number of lictors (12) and could only be vetoed by a reigning consul or praetor. Their abilities to govern were only limited by the decrees of the Senate or the people's assemblies, and the Tribune of the Plebs was unable to veto their acts as long as the governor remained at least a mile outside of Rome.

Censor
After a term as consul, the final step in the cursus honorum was the office of censor. This was the only office in the Roman Republic whose term was a period of eighteen months instead of the usual twelve. Censors were elected every five years and although the office held no military imperium, it was considered a great honour. The censors took a regular census of the people and then apportioned the citizens into voting classes on the basis of income and tribal affiliation. The censors enrolled new citizens in tribes and voting classes as well. The censors were also in charge of the membership roll of the Senate, every five years adding new senators who had been elected to the requisite offices. Censors could also remove unworthy members from the Senate. This ability was lost during the dictatorship of Sulla. Censors were also responsible for construction of public buildings and the moral status of the city.

Censors also had financial duties, in that they had to put out to tender projects that were to be financed by the state. Also, the censors were in charge of the leasing out of conquered land for public use and auction. Though this office owned no imperium, meaning no lictors for protection, they were allowed to wear the toga praetexta.

Tribune of the Plebs
The office of Tribune of the Plebs was an important step in the political career of plebeians. Patricians could not hold the office. They were not an official step in the cursus honorum. The Tribune was an office first created to protect the right of the common man in Roman politics and served as the head of the Plebeian Council. In the mid-to-late Republic, however, plebeians were often just as, and sometimes more, wealthy and powerful than patricians. Those who held the office were granted sacrosanctity (the right to be legally protected from any physical harm), the power to rescue any plebeian from the hands of a patrician magistrate, and the right to veto any act or proposal of any magistrate, including another tribune of the people and the consuls. The tribune also had the power to exercise capital punishment against any person who interfered in the performance of his duties. The tribunes could even convene a Senate meeting and lay legislation before it and arrest magistrates. Their houses had to remain open for visitors even during the night, and they were not allowed to be more than a day's journey from Rome. Due to their unique power of sacrosanctity, the Tribune had no need for lictors for protection and owned no imperium, nor could they wear the toga praetexta. For a period after Sulla's reforms, a person who had held the office of Tribune of the Plebs could no longer qualify for any other office, and the powers of the tribunes were more limited, but these restrictions were subsequently lifted.

Princeps senatus
Another office not officially a step in the cursus honorum was the princeps senatus, an extremely prestigious office for a patrician. The princeps senatus served as the leader of the Senate and was chosen to serve a five-year term by each pair of Censors every five years. Censors could, however, confirm a princeps senatus for a period of another five years. The princeps senatus was chosen from all Patricians who had served as a Consul, with former Censors usually holding the office. The office originally granted the holder the ability to speak first at session on the topic presented by the presiding magistrate, but eventually gained the power to open and close the senate sessions, decide the agenda, decide where the session should take place, impose order and other rules of the session, meet in the name of the senate with embassies of foreign countries, and write in the name of the senate letters and dispatches. This office, like the Tribune, did not own imperium, was not escorted by lictors, and could not wear the toga praetexta.

Dictator and magister equitum
Of all the offices within the Roman Republic, none granted as much power and authority as the position of dictator, known as the Master of the People. In times of emergency, the Senate would declare that a dictator was required, and the current consuls would appoint a dictator. This was the only decision that could not be vetoed by the Tribune of the Plebs. The dictator was the sole exception to the Roman legal principles of having multiple magistrates in the same office and being legally able to be held to answer for actions in office. Essentially by definition, only one dictator could serve at a time, and no dictator could ever be held legally responsible for any action during his time in office for any reason.

The dictator was the highest magistrate in degree of imperium and was attended by twenty-four lictors (as were the former Kings of Rome). Although his term lasted only six months instead of twelve (except for the Dictatorships of Sulla and Caesar), all other magistrates reported to the dictator (except for the tribunes of the plebs – although they could not veto any of the dictator's acts), granting the dictator absolute authority in both civil and military matters throughout the Republic. The dictator was free from the control of the Senate in all that he did, could execute anyone without a trial for any reason, and could ignore any law in the performance of his duties. The dictator was the sole magistrate under the Republic that was truly independent in discharging his duties. All of the other offices were extensions of the Senate's executive authority and thus answerable to the Senate. Since the dictator exercised his own authority, he did not suffer this limitation, which was the cornerstone of the office's power.

When a dictator entered office, he appointed to serve as his second-in-command a magister equitum, the Master of the Horse, whose office ceased to exist once the dictator left office. The magister equitum held praetorian imperium, was attended by six lictors, and was charged with assisting the dictator in managing the State. When the dictator was away from Rome, the magister equitum usually remained behind to administer the city. The magister equitum, like the dictator, had unchallengeable authority in all civil and military affairs, with his decisions only being overturned by the dictator himself.

The dictatorship was definitively abolished in 44 BC after the assassination of Gaius Julius Caesar (Lex Antonia).

title: Cursus honorum


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Talk:Lewis Carroll

Talking about Lewis Carroll's problematic history... without the CP.
CW/ CP, Child SA

I was sent here from the help desk to talk about this specific topic.

One day I was curious to dig into claims that Lewis Carroll was a pedo/groomer and took about (30?) of children, either nude or not. when I got to the section on the wikipedia page ( https://en.wikipedia.org/wiki/Lewis_Carroll ), there was undeniable evidence of one of them, as seen as a photo. Can we talk about the subject WITHOUT giving out the photo? It was taken a long time ago, but please. The last thing I wanna do is stumble upon CP because someone put it there. Thank you! — Preceding unsigned comment added by BloodyShard123 (talk • contribs) 21:47, 20 October 2021 (UTC)
 * In Victorian Britain, photos of pre-pubescent children naked or in rags were not considered (by "Polite society") to have any sexual implications, and were a popular genre in early photography. Queen Victoria and Prince Albert, active collectors of photographs, had a number of such pictures in their collection, some of them (if I recall correctly) actually taken by "Lewis Carroll" (Charles Dodgson), who was a pioneering and well-known amateur photographer. He took around 3,000 photos of various subjects, so it's not surprising that a small proportion of them would have been in this then-popular style. Have you already read the section Photography (1856–1880) in this very article?
 * Various writers, looking for sensational new angles on which to base literary-historical papers and books, have tried to push the conjecture that Carroll/Dodgson might have had paedophilic tendencies by using innuendo and forced interpretations, but as far as I'm aware (and as a fantasy writer he falls within my sphere of active interests), not a single shred of direct evidence has emerged to support it.
 * His image has also suffered from partisan efforts to portray him as Lewis Carroll the shy Oxford Don, when in fact he was a very convivial man with strong connections to the less fashionable North East of England. Read, if you can, Bryan Talbot's unconventional but cleverly designed and well-researched Alice in Sunderland, which presents a good deal of material about the real Charles Dodgson. {The poster formerly known as 87.81.230.195} 90.193.128.151 (talk) 22:33, 20 October 2021 (UTC)

 * Unless "CP" is short for Child Picture, there's no danger of anybody "stumbling" on anything in this article. Lewis Carroll took pictures of children (among other subjects). This has recently become controversial. We illustrate that with an example of one of his photographs of a child (fully clothed, albeit in rags). If you deem that photograph to be pornographic, that probably says more about you than it does about the photo.Chuntuk (talk) 12:31, 21 October 2021 (UTC)

 * , you should not have removed one of the pictures from the article. There is no consensus here to do so. I have reverted the removal. Wikignome Wintergreen talk 14:42, 21 October 2021 (UTC)
 * The BBC made a documentary called The Secret World of Lewis Carroll. It was inaccurate, saying a photograph of a naked prepubsecent girl was a picture of Lorina Liddell by Carroll, but actually it has been proved not to be by him, and is believed to be a medical photograph taken by a doctor, as the girl has a curved spine. I think the documentary should be mentioned, if only because lots of articles are still out there referring to the photograph and it's not clear that the documentary was discredited unless you read the imdb reviews. 92.40.9.166 (talk) 12:40, 29 July 2022 (UTC)
 * Here's why more detail on the inaccuracy -Two of the expert contributors on this programme complained to the BBC Trust about this programme and the BBC was censured by its own governing body for lying. The picture, supposedly recently discovered, had been readily accessible on the internet and known to scholars for around 20 years, and was known not to be authentic. The experts on Carroll who appeared on the programme were not told of it and thereby prevented from saying this. The provenance of the photo has no connection with England, let alone Carroll. It was bought from a French dealer one of whose specialities was 19th century French medical photographs, and the photo shows the girl's spine is crooked - a fact that was obscured by the BBC's selective use of the photo. The present owner of the photo, a museum, did not appear in the film, and has never claimed the photo is of Lorina by Carroll (it is only "attributed" based on an anonymous inscription on the back.) In fact the inscription uses the name "Lewis Carroll" which nobody in Carroll's lifetime would have used since he invariably used the name "Dodgson" and kept his identity as "Carroll" secret. When Lorina was a young teen he had not yet achieved fame as "Carroll" anyhow since he had not written "Alice in Wonderland" by then. The photo is also not in the format used by his specially made camera. It is only attributed to Carroll due to the date: Carroll was using photography at this time, but so were many hundreds of other photographers. It gives the non professional "gut feeling" of a consultant who is not a Lewis Carroll expert. However, I also read that 'The photographic conservation specialist Nicholas Burnett and forensic imagery analyst David Anley concluded it was authentic and probably of Liddell.' I'm still doubtful. Wakeling later wrote a scathing article in the Lewis Carroll Society Journal about his experiences on this documentary, and has managed to ensure it is never repeated, but I've been unable to find the article. The books of Wakeling and Robert Douglas-Fairhurst amy shed more light. 92.40.9.166 (talk) 13:13, 29 July 2022 (UTC)
 * From an opus of some 3,000 photographs, Edward Wakeling has calculated that nude photographs of children represent ‘no more than 1 per cent of Carroll’s output’.He argues that picturing nude children and focussing his camera on girls was common practice among Victorian photographers and that, when Carroll visited family friends, boys were more likely to be away at school.Is there a source for the John Betjeman quote about liking girls not boys? Betjeman was born eight years after Carroll died, so he couldn't have heard it directly from him. Wakeling says there are as well many photographs of boys and adults.
 * As a writer of children’s books, Carroll needed to explore children, Mr Wakeling pointed out: ‘His relationship with children is not an all-encompassing part of his life, which many of the biographers tried to suggest.
 * ‘He was a teacher. He actually enjoyed the intellectual banter that he could have with children. Children in Victorian times found that very refreshing because it was very uncommon for someone to treat them as equals. Children were seen and not heard.' Also Hugues Lebailly, Jenny Woolf and Karolina Leach would be interesting to reference. 92.40.9.166 (talk) 13:42, 29 July 2022 (UTC)
 * An oddity about the photo in question is that it has frequently been described as being of Lorina Liddell. The fact is the girl in the photo does not look like Lorina,  but does look like Edith L..  I say this assuming that the several photos of the Liddell children taken by Dodgson, and readily viewable on the net. have those three sisters correctly identified.  There is a strong family likeness between all three, so much so that Alice and Lorina would pass for identical twins were it not for the age difference. On the other hand Edith has markedly lower set eyebrows, as does the girl in the photo in question,  but very similar facial features otherwise.  To my eye the similarity between the face of the girl in this photo and others of Edith are so great as to make it almost certain that it is of her. 86.1.33.153 (talk) 11:52, 4 September 2022 (UTC)
 * It's also possible, that the photo of the girl doesn't depict any of the Liddell sisters. The face looks slightly bruised. And there seems to be an issue with the eyelid of the left (from dorsal view) eye. One thing is sure: The curators of the Musée Cantini won't confirm that the image had been taken by Dodgson. --DL5MDA (talk) 08:55, 20 February 2024 (UTC)
 * Response to the comment posted on 21:47, 20 October 2021 (top of this thread): As for claims that that Dodgson was a pedo/groomer, there is almost no academic research available. I recommend Katherine Wakely-Mulroney's The Man Who Loved Children: Lewis Carroll Studies’ Evidence Problem, Journal of the History of Sexuality, University of Texas Press, Vol. 30, № 3, pp. 335-362, 2021-09, https://www.academia.edu/67147027/The_Man_Who_Loved_Children_Lewis_Carroll_Studies_Evidence_Problem. --DL5MDA (talk) 09:46, 20 February 2024 (UTC)

pictures of children: dispute
It is claimed here that the pics of children were taken "often" in attendance of the parents. I don't think there is any evidence for this. Suspekt (talk) 13:35, 14 January 2024 (UTC)

Update: I removed the sentence. — Preceding unsigned comment added by Suspekt (talk • contribs) 21:50, 14 January 2024 (UTC)

 * Parents or chaperones. --DL5MDA (talk) 09:57, 20 February 2024 (UTC)

Dodgson
Every Carrollian knows that the "g" in Dodgson's name is silent. It is not pronounced. It is not supposed to be pronounced. It might be pronounced by some other people with the same name. Doesn't matter. This was discussed at length as far back as 2014, archived now, but it is still there. What can we do to stop people wrecking the IPA? -- Evertype·✆ 16:37, 26 June 2024 (UTC)
 * You could insert an invisible comment. pillow crow 17:09, 26 June 2024 (UTC)

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

title: Talk:Lewis Carroll


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Continental drift

Continental drift is the hypothesis, originating in the early 20th century, that Earth's continents move or drift relative to each other over geologic time. The hypothesis of continental drift has since been validated and incorporated into the science of plate tectonics, which studies the movement of the continents as they ride on plates of the Earth's lithosphere.

The speculation that continents might have "drifted" was first put forward by Abraham Ortelius in 1596. A pioneer of the modern view of mobilism was the Austrian geologist Otto Ampferer. The concept was independently and more fully developed by Alfred Wegener in his 1915 publication, "The Origin of Continents and Oceans". However, at that time the hypothesis was rejected by many for lack of any motive mechanism. In 1931, the English geologist Arthur Holmes proposed mantle convection for that mechanism.

Early history

Abraham Ortelius, Theodor Christoph Lilienthal (1756), Alexander von Humboldt (1801 and 1845), Antonio Snider-Pellegrini , and others had noted earlier that the shapes of continents on opposite sides of the Atlantic Ocean (most notably, Africa and South America) seem to fit together. W. J. Kious described Ortelius' thoughts in this way: "Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were 'torn away from Europe and Africa ... by earthquakes and floods' and went on to say: 'The vestiges of the rupture reveal themselves if someone brings forward a map of the world and considers carefully the coasts of the three [continents].'"

In 1889, Alfred Russel Wallace remarked, "It was formerly a very general belief, even amongst geologists, that the great features of the earth's surface, no less than the smaller ones, were subject to continual mutations, and that during the course of known geological time the continents and great oceans had, again and again, changed places with each other." He quotes Charles Lyell as saying, "Continents, therefore, although permanent for whole geological epochs, shift their positions entirely in the course of ages." and claims that the first to throw doubt on this was James Dwight Dana in 1849.

In his Manual of Geology (1863), Dana wrote, "The continents and oceans had their general outline or form defined in earliest time. This has been proved with regard to North America from the position and distribution of the first beds of the Lower Silurian, – those of the Potsdam epoch. The facts indicate that the continent of North America had its surface near tide-level, part above and part below it (p.196); and this will probably be proved to be the condition in Primordial time of the other continents also. And, if the outlines of the continents were marked out, it follows that the outlines of the oceans were no less so". Dana was enormously influential in America—his Manual of Mineralogy is still in print in revised form—and the theory became known as the Permanence theory.

This appeared to be confirmed by the exploration of the deep sea beds conducted by the Challenger expedition, 1872–1876, which showed that contrary to expectation, land debris brought down by rivers to the ocean is deposited comparatively close to the shore on what is now known as the continental shelf. This suggested that the oceans were a permanent feature of the Earth's surface, rather than them having "changed places" with the continents.

Eduard Suess had proposed a supercontinent Gondwana in 1885 and the Tethys Ocean in 1893, assuming a land-bridge between the present continents submerged in the form of a geosyncline, and John Perry had written an 1895 paper proposing that the Earth's interior was fluid, and disagreeing with Lord Kelvin on the age of the Earth.

Wegener and his predecessors

Apart from the earlier speculations mentioned above, the idea that the American continents had once formed a single landmass with Eurasia and Africa was postulated by several scientists before Alfred Wegener's 1912 paper. Although Wegener's theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas: Franklin Coxworthy (between 1848 and 1890), Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907) and Frank Bursley Taylor (1908).

The similarity of southern continent geological formations had led Roberto Mantovani to conjecture in 1889 and 1909 that all the continents had once been joined into a supercontinent; Wegener noted the similarity of Mantovani's and his own maps of the former positions of the southern continents. In Mantovani's conjecture, this continent broke due to volcanic activity caused by thermal expansion, and the new continents drifted away from each other because of further expansion of the rip-zones, where the oceans now lie. This led Mantovani to propose a now-discredited Expanding Earth theory.

Continental drift without expansion was proposed by Frank Bursley Taylor, who suggested in 1908 (published in 1910) that the continents were moved into their present positions by a process of "continental creep", later proposing a mechanism of increased tidal forces during the Cretaceous dragging the crust towards the equator. He was the first to realize that one of the effects of continental motion would be the formation of mountains, attributing the formation of the Himalayas to the collision between the Indian subcontinent with Asia. Wegener said that of all those theories, Taylor's had the most similarities to his own. For a time in the mid-20th century, the theory of continental drift was referred to as the "Taylor-Wegener hypothesis".

Alfred Wegener first presented his hypothesis to the German Geological Society on 6 January 1912. His hypothesis was that the continents had once formed a single landmass, called Pangaea, before breaking apart and drifting to their present locations.

Wegener was the first to use the phrase "continental drift" (1912, 1915) (in German "die Verschiebung der Kontinente" – translated into English in 1922) and formally publish the hypothesis that the continents had somehow "drifted" apart. Although he presented much evidence for continental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. He suggested that the continents had been pulled apart by the centrifugal pseudoforce (Polflucht) of the Earth's rotation or by a small component of astronomical precession, but calculations showed that the force was not sufficient. The Polflucht hypothesis was also studied by Paul Sophus Epstein in 1920 and found to be implausible.

Rejection of Wegener's theory, 1910s–1950s
Although now accepted, and even with a minority of scientific proponents over the decades, the theory of continental drift was largely rejected for many years, with evidence in its favor considered insufficient. One problem was that a plausible driving force was missing. A second problem was that Wegener's estimate of the speed of continental motion, 250 cm/year, was implausibly high. (The currently accepted rate for the separation of the Americas from Europe and Africa is about 2.5 cm/year). Furthermore, Wegener was treated less seriously because he was not a geologist. Even today, the details of the forces propelling the plates are poorly understood.

The English geologist Arthur Holmes championed the theory of continental drift at a time when it was deeply unfashionable. He proposed in 1931 that the Earth's mantle contained convection cells which dissipated heat produced by radioactive decay and moved the crust at the surface. His Principles of Physical Geology, ending with a chapter on continental drift, was published in 1944.

Geological maps of the time showed huge land bridges spanning the Atlantic and Indian oceans to account for the similarities of fauna and flora and the divisions of the Asian continent in the Permian period, but failing to account for glaciation in India, Australia and South Africa.

The fixists
Hans Stille and Leopold Kober opposed the idea of continental drift and worked on a "fixist" geosyncline model with Earth contraction playing a key role in the formation of orogens. Other geologists who opposed continental drift were Bailey Willis, Charles Schuchert, Rollin Chamberlin, Walther Bucher and Walther Penck. In 1939 an international geological conference was held in Frankfurt. This conference came to be dominated by the fixists, especially as those geologists specializing in tectonics were all fixists except Willem van der Gracht. Criticism of continental drift and mobilism was abundant at the conference not only from tectonicists but also from sedimentological (Nölke), paleontological (Nölke), mechanical (Lehmann) and oceanographic (Troll, Wüst) perspectives. Hans Cloos, the organizer of the conference, was also a fixist who together with Troll held the view that excepting the Pacific Ocean continents were not radically different from oceans in their behaviour. The mobilist theory of Émile Argand for the Alpine orogeny was criticized by Kurt Leuchs. The few drifters and mobilists at the conference appealed to biogeography (Kirsch, Wittmann), paleoclimatology (Wegener, K), paleontology (Gerth) and geodetic measurements (Wegener, K). F. Bernauer correctly equated Reykjanes in south-west Iceland with the Mid-Atlantic Ridge, arguing with this that the floor of the Atlantic Ocean was undergoing extension just like Reykjanes. Bernauer thought this extension had drifted the continents only 100–200 km apart, the approximate width of the volcanic zone in Iceland.

David Attenborough, who attended university in the second half of the 1940s, recounted an incident illustrating its lack of acceptance then: "I once asked one of my lecturers why he was not talking to us about continental drift and I was told, sneeringly, that if I could prove there was a force that could move continents, then he might think about it. The idea was moonshine, I was informed."

As late as 1953—just five years before Carey introduced the theory of plate tectonics—the theory of continental drift was rejected by the physicist Scheidegger on the following grounds.
 * First, it had been shown that floating masses on a rotating geoid would collect at the equator, and stay there. This would explain one, but only one, mountain building episode between any pair of continents; it failed to account for earlier orogenic episodes.
 * Second, masses floating freely in a fluid substratum, like icebergs in the ocean, should be in isostatic equilibrium (in which the forces of gravity and buoyancy are in balance). But gravitational measurements showed that many areas are not in isostatic equilibrium.
 * Third, there was the problem of why some parts of the Earth's surface (crust) should have solidified while other parts were still fluid. Various attempts to explain this foundered on other difficulties.

Road to acceptance
From the 1930s to the late 1950s, works by Vening-Meinesz, Holmes, Umbgrove, and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea, and in 1928 that convection currents within the mantle might be the driving force. Holmes' views were particularly influential: in his bestselling textbook, Principles of Physical Geology, he included a chapter on continental drift, proposing that Earth's mantle contained convection cells which dissipated radioactive heat and moved the crust at the surface. Holmes' proposal resolved the phase disequilibrium objection (the underlying fluid was kept from solidifying by radioactive heating from the core). However, scientific communication in the 1930s and 1940s was inhibited by World War II, and the theory still required work to avoid foundering on the orogeny and isostasy objections. Worse, the most viable forms of the theory predicted the existence of convection cell boundaries reaching deep into the Earth, that had yet to be observed.

In 1947, a team of scientists led by Maurice Ewing confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath the sediments was chemically and physically different from continental crust. As oceanographers continued to bathymeter the ocean basins, a system of mid-oceanic ridges was detected. An important conclusion was that along this system, new ocean floor was being created, which led to the concept of the "Great Global Rift".

Meanwhile, scientists began recognizing odd magnetic variations across the ocean floor using devices developed during World War II to detect submarines. Over the next decade, it became increasingly clear that the magnetization patterns were not anomalies, as had been originally supposed. In a series of papers published between 1959 and 1963, Heezen, Dietz, Hess, Mason, Vine, Matthews, and Morley collectively realized that the magnetization of the ocean floor formed extensive, zebra-like patterns: one stripe would exhibit normal polarity and the adjoining stripes reversed polarity. The best explanation was the "conveyor belt" or Vine–Matthews–Morley hypothesis. New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. The new crust is magnetized by the Earth's magnetic field, which undergoes occasional reversals. Formation of new crust then displaces the magnetized crust apart, akin to a conveyor belt – hence the name.

Without workable alternatives to explain the stripes, geophysicists were forced to conclude that Holmes had been right: ocean rifts were sites of perpetual orogeny at the boundaries of convection cells. By 1967, barely two decades after discovery of the mid-oceanic rifts, and a decade after discovery of the striping, plate tectonics had become axiomatic to modern geophysics.

In addition, Marie Tharp, in collaboration with Bruce Heezen, who was initially sceptical of Tharp's observations that her maps confirmed continental drift theory, provided essential corroboration, using her skills in cartography and seismographic data, to confirm the theory.

Modern evidence
Geophysicist Jack Oliver is credited with providing seismologic evidence supporting plate tectonics which encompassed and superseded continental drift with the article "Seismology and the New Global Tectonics", published in 1968, using data collected from seismologic stations, including those he set up in the South Pacific. The modern theory of plate tectonics, refining Wegener, explains that there are two kinds of crust of different composition: continental crust and oceanic crust, both floating above a much deeper "plastic" mantle. Continental crust is inherently lighter. Oceanic crust is created at spreading centers, and this, along with subduction, drives the system of plates in a chaotic manner, resulting in continuous orogeny and areas of isostatic imbalance.

Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around the shores of different continents, suggesting that they were once joined. The fossils of Mesosaurus, a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa, are one example; another is the discovery of fossils of the land reptile Lystrosaurus in rocks of the same age at locations in Africa, India, and Antarctica. There is also living evidence, with the same animals being found on two continents. Some earthworm families (such as Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa.

The complementary arrangement of the facing sides of South America and Africa is an obvious and temporary coincidence. In millions of years, slab pull, ridge-push, and other forces of tectonophysics will further separate and rotate those two continents. It was that temporary feature that inspired Wegener to study what he defined as continental drift although he did not live to see his hypothesis generally accepted.

The widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, based on continents' current positions and orientations, and supported the idea that the southern continents had previously been in dramatically different locations that were contiguous with one another.

title: Continental drift


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Commodores

Commodores, often billed as the Commodores, are an American funk and soul group. The group's most successful period was in the late 1970s and early 1980s when Lionel Richie was the co-lead singer.

The members of the group met as mostly freshmen at Tuskegee Institute (now Tuskegee University) in 1968, and signed with Motown in November 1972, having first caught the public eye opening for the Jackson 5 while on tour.

The band's biggest hit singles are ballads such as "Easy", "Three Times a Lady", and "Nightshift"; and funk-influenced dance songs, including "Brick House", "Fancy Dancer", "Lady (You Bring Me Up)", and "Too Hot ta Trot".

Commodores were inducted into the Alabama Music Hall of Fame and Vocal Group Hall of Fame. The band has also won one Grammy Award out of nine nominations. The Commodores have sold over 70 million albums worldwide.

History
Commodores were formed from two former student groups, the Mystics and the Jays. Richie described some members of the Mystics as "jazz buffs". The new six-man band featured Lionel Richie, Thomas McClary, and William King from the Mystics, and Andre Callahan, Michael Gilbert, and Milan Williams from the Jays. They chose their present name when King flipped open a dictionary and ran his finger down the page. "We lucked out," he remarked with a laugh when telling this story to People magazine. "We almost became 'The Commodes.'"

The bandmembers attended Tuskegee University in Alabama. After winning the university's annual freshman talent contest, they played at fraternity parties as well as a weekend gig at the Black Forest Inn, one of a few clubs in Tuskegee that catered to college students. They performed cover tunes and some original songs with their first singer, James Ingram (not the famous solo artist). Ingram, older than the rest of the band, left to serve in Vietnam, and was later replaced by drummer Walter "Clyde" Orange, who wrote or co-wrote many of their hits. Lionel Richie and Orange alternated as lead singers. Orange was the lead singer on the Top 10 hits "Brick House" (1977) and "Nightshift" (1985).

The early band was managed by Benny Ashburn, who brought them to his family's vacation lodge on Martha's Vineyard in 1971 and 1972. There, Ashburn test-marketed the group by having them play in parking lots and summer festivals. "Machine Gun" (1974), the instrumental title track from the band's debut album, became a staple at American sporting events, and is also heard in many films, including Boogie Nights and Looking for Mr. Goodbar. It reached No. 22 on the Billboard Hot 100 in 1974. Another 1974 song "I Feel Sanctified" has been called a "prototype" of Wild Cherry's 1976 big hit "Play That Funky Music". Of the three albums released in 1975 and 1976, Caught in the Act was funk album, but Movin' On and Hot on the Tracks were pop albums. After those recordings the group developed the mellower sound hinted at in their 1976 top-ten hits, "Sweet Love" and "Just to Be Close to You". In 1977, the Commodores released "Easy", which became the group's biggest hit yet, reaching No. 4 in the US, followed by funky single "Brick House", also top 5, both from their album Commodores, as was "Zoom". The group reached No. 1 in 1978 with "Three Times a Lady". In 1979, the Commodores scored another top-five ballad, "Sail On", before reaching the top of the charts once again with another ballad, "Still". In 1981 they released two top-ten hits with "Oh No" (No. 4) and their first upbeat single in almost five years, "Lady (You Bring Me Up)" (No. 8).

Commodores made a brief appearance in the 1978 film Thank God It's Friday. They performed the song "Too Hot ta Trot" during the dance contest; the songs "Brick House" and "Easy" were also played in the movie

In 1982, the group decided to take a hiatus from touring and recording, during which time Lionel Richie recorded a solo album at the suggestion of Motown and the other group members. Its success encouraged Richie to pursue a solo career, and Skyler Jett replaced him as co-lead singer. Also in 1982, Ashburn died of a heart attack at the age of 54. Founding member McClary left in 1984 (shortly after Richie) to pursue a solo career, and to develop a gospel music company. McClary was replaced by guitarist-vocalist Sheldon Reynolds. Then LaPread left in 1986 and moved to Auckland, New Zealand. Reynolds departed for Earth, Wind & Fire in 1987, which prompted trumpeter William "WAK" King to take over primary guitar duties for live performances. Keyboardist Milan Williams exited the band in 1989 after allegedly refusing to tour South Africa.

The group gradually abandoned its funk roots and moved into the more commercial pop arena. In 1984, former Heatwave singer James Dean "J.D." Nicholas assumed co-lead vocal duties with drummer Walter Orange. That line-up was hitless until 1985 when their final Motown album Nightshift, produced by Dennis Lambert (prior albums were produced by James Anthony Carmichael), delivered the title track "Nightshift", a loving tribute to Marvin Gaye and Jackie Wilson, both of whom had died the previous year. "Nightshift" hit no. 3 in the US and won the Commodores their first Grammy for Best R&B Performance by a Duo or Group With Vocals in 1985.

In 2010 a new version was recorded, dedicated to Michael Jackson. The Commodores were on a European tour performing at Wembley Arena, London, on June 25, 2009, when they walked off the stage after they were told that Michael Jackson had died. Initially the band thought it was a hoax. However, back in their dressing rooms they received confirmation and broke down in tears. The next night at Birmingham's NIA Arena, J.D. Nicholas added Jackson's name to the lyrics of the song, and henceforth the Commodores have mentioned Jackson and other deceased R&B singers. Thus came the inspiration upon the first anniversary of Jackson's death to re-record, with new lyrics, the hit song "Nightshift" as a tribute.

In 1990, they formed Commodores Records and re-recorded their 20 greatest hits as Commodores Hits Vol. I & II. They have recorded a live album, Commodores Live, along with a DVD of the same name, and a Christmas album titled Commodores Christmas. In 2012, the band was working on new material, with some contributions written by current and former members.

Commodores as of 2020 consist of Walter "Clyde" Orange, James Dean "J.D." Nicholas, and William "WAK" King, along with their five-piece band The Mean Machine.They continue to perform, playing at arenas, theaters, and festivals around the world.

Current members

 * William "WAK" King – trumpet, guitar, keyboards, vocals (1968–present)
 * Walter Orange – vocals, drums (1972–present)
 * James Dean "J.D." Nicholas – vocals (1984–present)

Former members

 * Lionel Richie – vocals, keyboards, saxophone (1968–82)
 * Milan Williams – keyboards, rhythm guitar (1968–89)
 * Thomas McClary – lead guitar, vocals (1968–83)
 * Andre Callahan – drums, vocals, keyboards (1968–70)
 * Michael Gilbert – bass guitar, trumpet (1968–70)
 * Eugene Ward – keyboards (1968–70)
 * Ronald LaPread – bass guitar (1970–86)
 * James Ingram – vocals, drums (1970–72)
 * Skyler Jett – vocals (1982–84)
 * Sheldon Reynolds – lead guitar (1983–87)
 * Mikael Manley – lead guitar (1995–2005)
 * Don Williams Sr - keyboards (1999-2001)

Discography

 * Studio albums
 * Machine Gun (1974)
 * Caught in the Act (1975)
 * Movin' On (1975)
 * Hot on the Tracks (1976)
 * Commodores (1977)
 * Natural High (1978)
 * Midnight Magic (1979)
 * Heroes (1980)
 * In the Pocket (1981)
 * Commodores 13 (1983)
 * Nightshift (1985)
 * United (1986)
 * Rock Solid (1988)
 * No Tricks (1993)

Grammy awards
The Commodores have won one Grammy Award out of ten nominations.

Alabama Music Hall of Fame
During 1995 the Commodores were inducted into the Alabama Music Hall of Fame.

Vocal Group Hall of Fame
During 2003 the Commodores were also inducted into the Vocal Group Hall of Fame.

title: Commodores


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Collagen

Collagen is the main structural protein in the extracellular matrix of a body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals. 25% to 35% of a mammalian body's protein content is collagen. Amino acids are bound together to form a triple helix of elongated fibril known as a collagen helix. The collagen helix is mostly found in connective tissue such as cartilage, bones, tendons, ligaments, and skin. Vitamin C is vital for collagen synthesis, and Vitamin E improves the production of collagen. Depending upon the degree of mineralization, collagen tissues may be rigid (bone) or compliant (tendon) or have a gradient from rigid to compliant (cartilage). Collagen is also abundant in corneas, blood vessels, the gut, intervertebral discs, and the dentin in teeth. In muscle tissue, it serves as a major component of the endomysium. Collagen constitutes 1% to 2% of muscle tissue and accounts for 6% of the weight to skeletal muscle. The fibroblast is the most common cell creating collagen in a body. Gelatin, which is used in food and industry, is collagen that was irreversibly hydrolyzed using heat, basic solutions, or weak acids.

Etymology

The name collagen comes from the Greek κόλλα (kólla), meaning "glue", and suffix -γέν, -gen, denoting "producing".

Human types
Over 90% of the collagen in the human body is type I collagen. However, as of 2011, 28 types of human collagen have been identified, described, and divided into several groups according to the structure they form. All of the types contain at least one triple helix. The number of types shows collagen's diverse functionality.
 * Fibrillar (Type I, II, III, V, XI)
 * Non-fibrillar
 * FACIT (Fibril Associated Collagens with Interrupted Triple Helices) (Type IX, XII, XIV, XIX, XXI)
 * Short chain (Type VIII, X)
 * Basement membrane (Type IV)
 * Multiplexin (Multiple Triple Helix domains with Interruptions) (Type XV, XVIII)
 * MACIT (Membrane Associated Collagens with Interrupted Triple Helices) (Type XIII, XVII)
 * Microfibril forming (Type VI)
 * Anchoring fibrils (Type VII)

The five most common types are:
 * Type I: skin, tendon, vasculature, organs, bone (main component of the organic part of bone)
 * Type II: cartilage (main collagenous component of cartilage)
 * Type III: reticulate (main component of reticular fibers), commonly found alongside type I
 * Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane
 * Type V: cell surfaces, hair, and placenta

Cardiac
The collagenous cardiac skeleton which includes the four heart valve rings, is histologically, elastically and uniquely bound to cardiac muscle. The cardiac skeleton also includes the separating septa of the heart chambers – the interventricular septum and the atrioventricular septum. Collagen contribution to the measure of cardiac performance summarily represents a continuous torsional force opposed to the fluid mechanics of blood pressure emitted from the heart. The collagenous structure that divides the upper chambers of the heart from the lower chambers is an impermeable membrane that excludes both blood and electrical impulses through typical physiological means. With support from collagen, atrial fibrillation never deteriorates to ventricular fibrillation. Collagen is layered in variable densities with smooth muscle mass. The mass, distribution, age, and density of collagen all contribute to the compliance required to move blood back and forth. Individual cardiac valvular leaflets are folded into shape by specialized collagen under variable pressure. Gradual calcium deposition within collagen occurs as a natural function of aging. Calcified points within collagen matrices show contrast in a moving display of blood and muscle, enabling methods of cardiac imaging technology to arrive at ratios essentially stating blood in (cardiac input) and blood out (cardiac output). Pathology of the collagen underpinning of the heart is understood within the category of connective tissue disease.

Bone grafts
As the skeleton forms the structure of the body, it is vital that it maintains its strength, even after breaks and injuries. Collagen is used in bone grafting as it has a triple helical structure, making it a very strong molecule. It is ideal for use in bones, as it does not compromise the structural integrity of the skeleton. The triple helical structure of collagen prevents it from being broken down by enzymes, it enables adhesiveness of cells and it is important for the proper assembly of the extracellular matrix.

Tissue regeneration
Collagen scaffolds are used in tissue regeneration, whether in sponges, thin sheets, gels, or fibers. Collagen has favorable properties for tissue regeneration, such as pore structure, permeability, hydrophilicity, and stability in vivo. Collagen scaffolds also support deposition of cells, such as osteoblasts and fibroblasts, and once inserted, facilitate growth to proceed normally.

Reconstructive surgical uses
Collagens are widely employed in the construction of artificial skin substitutes used in the management of severe burns and wounds. These collagens may be derived from bovine, equine, porcine, or even human sources; and are sometimes used in combination with silicones, glycosaminoglycans, fibroblasts, growth factors and other substances.

Wound healing
Collagen is one of the body's key natural resources and a component of skin tissue that can benefit all stages of wound healing. When collagen is made available to the wound bed, closure can occur. Wound deterioration, followed sometimes by procedures such as amputation, can thus be avoided.

Collagen is a natural product and is thus used as a natural wound dressing and has properties that artificial wound dressings do not have. It is resistant against bacteria, which is of vital importance in a wound dressing. It helps to keep the wound sterile, because of its natural ability to fight infection. When collagen is used as a burn dressing, healthy granulation tissue is able to form very quickly over the burn, helping it to heal rapidly.

Throughout the four phases of wound healing, collagen performs the following functions:
 * Guiding function: Collagen fibers serve to guide fibroblasts. Fibroblasts migrate along a connective tissue matrix.
 * Chemotactic properties: The large surface area available on collagen fibers can attract fibrogenic cells which help in healing.
 * Nucleation: Collagen, in the presence of certain neutral salt molecules, can act as a nucleating agent causing formation of fibrillar structures.
 * Hemostatic properties: Blood platelets interact with the collagen to make a hemostatic plug.

Basic research
Collagen is used in laboratory studies for cell culture, studying cell behavior and cellular interactions with the extracellular environment. Collagen is also widely used as a bioink for 3D bioprinting and biofabrication of 3D tissue models.

Biology
The collagen protein is composed of a triple helix, which generally consists of two identical chains (α1) and an additional chain that differs slightly in its chemical composition (α2). The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content. The most common motifs in the amino acid sequence of collagen are glycine-proline-X and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline or hydroxyproline. The average amino acid composition for fish and mammal skin is given.

Synthesis
First, a three-dimensional stranded structure is assembled with amino acids glycine and proline as its principal components. This is not yet collagen but is its precursor: procollagen. Procollagen is then modified by the addition of hydroxyl groups to the amino acids proline and lysine. This step is important for later glycosylation and the formation of a triple helix structure to collagen. Because the hydroxylase enzymes performing these reactions require vitamin C as a cofactor, a long-term deficiency in this vitamin results in impaired collagen synthesis and scurvy. These hydroxylation reactions are catalyzed by two different enzymes: prolyl 4-hydroxylase and lysyl hydroxylase. The reaction consumes one ascorbate molecule per hydroxylation. The synthesis of collagen occurs inside and outside of a cell. The formation of collagen which results in fibrillary collagen (most common form) is discussed here. Meshwork collagen, which is often involved in the formation of filtration systems, is another common form of collagen. All types of collagens are triple helices, and the differences lie in the make-up of their alpha peptides created in step 2.
 * 1) Transcription of mRNA: About 44 genes are associated with collagen formation, each coding for a specific mRNA sequence, and typically have the "COL" prefix. The beginning of collagen synthesis begins with turning on genes associated with the formation of a particular alpha peptide (typically alpha 1, 2 or 3).
 * 2) Pre-pro-peptide formation: Once the final mRNA exits from the cell nucleus and enters into the cytoplasm, it links with the ribosomal subunits and the process of translation occurs. The early/first part of the new peptide is known as the signal sequence. The signal sequence on the N-terminal of the peptide is recognized by a signal recognition particle on the endoplasmic reticulum, which will be responsible for directing the pre-pro-peptide into the endoplasmic reticulum. Therefore, once the synthesis of new peptide is finished, it goes directly into the endoplasmic reticulum for post-translational processing. It is now known as preprocollagen.
 * 3) Pre-pro-peptide to pro-collagen: Three modifications of the pre-pro-peptide occur leading to the formation of the alpha peptide:
 * 4) The signal peptide on the N-terminal is removed, and the molecule is now known as propeptide (not procollagen).
 * 5) Hydroxylation of lysines and prolines on propeptide by the enzymes 'prolyl hydroxylase' and 'lysyl hydroxylase' (to produce hydroxyproline and hydroxylysine) occurs to aid cross-linking of the alpha peptides. This enzymatic step requires vitamin C as a cofactor. In scurvy, the lack of hydroxylation of prolines and lysines causes a looser triple helix (which is formed by three alpha peptides).
 * 6) Glycosylation occurs by adding either glucose or galactose monomers onto the hydroxyl groups that were placed onto lysines, but not on prolines.
 * 7) Once these modifications have taken place, three of the hydroxylated and glycosylated propeptides twist into a triple helix forming procollagen. Procollagen still has unwound ends, which will be later trimmed. At this point, the procollagen is packaged into a transfer vesicle destined for the Golgi apparatus.
 * 8) Golgi apparatus modification: In the Golgi apparatus, the procollagen goes through one last post-translational modification before being secreted out of the cell. In this step, oligosaccharides (not monosaccharides as in step 3) are added, and then the procollagen is packaged into a secretory vesicle destined for the extracellular space.
 * 9) Formation of tropocollagen: Once outside the cell, membrane bound enzymes known as collagen peptidases, remove the "loose ends" of the procollagen molecule. What is left is known as tropocollagen. Defects in this step produce one of the many collagenopathies known as Ehlers–Danlos syndrome. This step is absent when synthesizing type III, a type of fibrillar collagen.
 * 10) Formation of the collagen fibril: lysyl oxidase, an extracellular copper-dependent enzyme, produces the final step in the collagen synthesis pathway. This enzyme acts on lysines and hydroxylysines producing aldehyde groups, which will eventually undergo covalent bonding between tropocollagen molecules. This polymer of tropocollagen is known as a collagen fibril.

Amino acids
Collagen has an unusual amino acid composition and sequence:
 * Glycine is found at almost every third residue.
 * Proline makes up about 17% of collagen.
 * Collagen contains two unusual derivative amino acids not directly inserted during translation. These amino acids are found at specific locations relative to glycine and are modified post-translationally by different enzymes, both of which require vitamin C as a cofactor.
 * Hydroxyproline derived from proline
 * Hydroxylysine derived from lysine – depending on the type of collagen, varying numbers of hydroxylysines are glycosylated (mostly having disaccharides attached).

Cortisol stimulates degradation of (skin) collagen into amino acids.

Collagen I formation
Most collagen forms in a similar manner, but the following process is typical for type I:

 * 1) Inside the cell
 * 2) Two types of alpha chains – alpha-1 and alpha 2, are formed during translation on ribosomes along the rough endoplasmic reticulum (RER). These peptide chains known as preprocollagen, have registration peptides on each end and a signal peptide.
 * 3) Polypeptide chains are released into the lumen of the RER.
 * 4) Signal peptides are cleaved inside the RER and the chains are now known as pro-alpha chains.
 * 5) Hydroxylation of lysine and proline amino acids occurs inside the lumen. This process is dependent on and consumes ascorbic acid (vitamin C) as a cofactor.
 * 6) Glycosylation of specific hydroxylysine residues occurs.
 * 7) Triple alpha helical structure is formed inside the endoplasmic reticulum from two alpha-1 chains and one alpha-2 chain.
 * 8) Procollagen is shipped to the Golgi apparatus, where it is packaged and secreted into extracellular space by exocytosis.
 * 9) Outside the cell
 * 10) Registration peptides are cleaved and tropocollagen is formed by procollagen peptidase.
 * 11) Multiple tropocollagen molecules form collagen fibrils, via covalent cross-linking (aldol reaction) by lysyl oxidase which links hydroxylysine and lysine residues. Multiple collagen fibrils form into collagen fibers.
 * 12) Collagen may be attached to cell membranes via several types of protein, including fibronectin, laminin, fibulin and integrin.

Synthetic pathogenesis
Vitamin C is crucial for maintaining a healthy collagen network in humans by preventing the inactivation of key enzymes involved in collagen production. One study evaluated the effects of Vitamin C on collagen synthesis and cross-linking in normal human fibroblasts. The findings demonstrated that Vitamin C increases collagen type I deposits and enhances extracellular matrix contraction in a dose-dependent manner. Additionally, two Vitamin C derivatives, Vitamin C-phosphate (VitC-P) and Vitamin C-glucoside (VitC-Glu), showed similar beneficial effects on collagen synthesis, suggesting they could be used as stable alternatives in anti-aging products.

Vitamin C deficiency causes scurvy, a serious and painful disease in which defective collagen prevents the formation of strong connective tissue. Gums deteriorate and bleed, with loss of teeth; skin discolors, and wounds do not heal. Prior to the 18th century, this condition was notorious among long-duration military, particularly naval, expeditions during which participants were deprived of foods containing vitamin C.

An autoimmune disease such as lupus erythematosus or rheumatoid arthritis may attack healthy collagen fibers.

Many bacteria and viruses secrete virulence factors, such as the enzyme collagenase, which destroys collagen or interferes with its production.

Molecular structure
A single collagen molecule, tropocollagen, is used to make up larger collagen aggregates, such as fibrils. It is approximately 300 nm long and 1.5 nm in diameter, and it is made up of three polypeptide strands (called alpha peptides, see step 2), each of which has the conformation of a left-handed helix – this should not be confused with the right-handed alpha helix. These three left-handed helices are twisted together into a right-handed triple helix or "super helix", a cooperative quaternary structure stabilized by many hydrogen bonds. With type I collagen and possibly all fibrillar collagens, if not all collagens, each triple-helix associates into a right-handed super-super-coil referred to as the collagen microfibril. Each microfibril is interdigitated with its neighboring microfibrils to a degree that might suggest they are individually unstable, although within collagen fibrils, they are so well ordered as to be crystalline.

A distinctive feature of collagen is the regular arrangement of amino acids in each of the three chains of these collagen subunits. The sequence often follows the pattern Gly-Pro-X or Gly-X-Hyp, where X may be any of various other amino acid residues. Proline or hydroxyproline constitute about 1/6 of the total sequence. With glycine accounting for the 1/3 of the sequence, this means approximately half of the collagen sequence is not glycine, proline or hydroxyproline, a fact often missed due to the distraction of the unusual GX1X2 character of collagen alpha-peptides. The high glycine content of collagen is important with respect to stabilization of the collagen helix as this allows the very close association of the collagen fibers within the molecule, facilitating hydrogen bonding and the formation of intermolecular cross-links. This kind of regular repetition and high glycine content is found in only a few other fibrous proteins, such as silk fibroin.

Collagen is not only a structural protein. Due to its key role in the determination of cell phenotype, cell adhesion, tissue regulation, and infrastructure, many sections of its non-proline-rich regions have cell or matrix association/regulation roles. The relatively high content of proline and hydroxyproline rings, with their geometrically constrained carboxyl and (secondary) amino groups, along with the rich abundance of glycine, accounts for the tendency of the individual polypeptide strands to form left-handed helices spontaneously, without any intrachain hydrogen bonding.

Because glycine is the smallest amino acid with no side chain, it plays a unique role in fibrous structural proteins. In collagen, Gly is required at every third position because the assembly of the triple helix puts this residue at the interior (axis) of the helix, where there is no space for a larger side group than glycine's single hydrogen atom. For the same reason, the rings of the Pro and Hyp must point outward. These two amino acids help stabilize the triple helix – Hyp even more so than Pro; a lower concentration of them is required in animals such as fish, whose body temperatures are lower than most warm-blooded animals. Lower proline and hydroxyproline contents are characteristic of cold-water, but not warm-water fish; the latter tend to have similar proline and hydroxyproline contents to mammals. The lower proline and hydroxyproline contents of cold-water fish and other poikilotherm animals leads to their collagen having a lower thermal stability than mammalian collagen. This lower thermal stability means that gelatin derived from fish collagen is not suitable for many food and industrial applications.

The tropocollagen subunits spontaneously self-assemble, with regularly staggered ends, into even larger arrays in the extracellular spaces of tissues. Additional assembly of fibrils is guided by fibroblasts, which deposit fully formed fibrils from fibripositors. In the fibrillar collagens, molecules are staggered to adjacent molecules by about 67 nm (a unit that is referred to as 'D' and changes depending upon the hydration state of the aggregate). In each D-period repeat of the microfibril, there is a part containing five molecules in cross-section, called the "overlap", and a part containing only four molecules, called the "gap". These overlap and gap regions are retained as microfibrils assemble into fibrils, and are thus viewable using electron microscopy. The triple helical tropocollagens in the microfibrils are arranged in a quasihexagonal packing pattern. There is some covalent crosslinking within the triple helices and a variable amount of covalent crosslinking between tropocollagen helices forming well-organized aggregates (such as fibrils). Larger fibrillar bundles are formed with the aid of several different classes of proteins (including different collagen types), glycoproteins, and proteoglycans to form the different types of mature tissues from alternate combinations of the same key players. Collagen's insolubility was a barrier to the study of monomeric collagen until it was found that tropocollagen from young animals can be extracted because it is not yet fully crosslinked. However, advances in microscopy techniques (i.e. electron microscopy (EM) and atomic force microscopy (AFM)) and X-ray diffraction have enabled researchers to obtain increasingly detailed images of collagen structure in situ. These later advances are particularly important to better understanding the way in which collagen structure affects cell–cell and cell–matrix communication and how tissues are constructed in growth and repair and changed in development and disease. For example, using AFM–based nanoindentation it has been shown that a single collagen fibril is a heterogeneous material along its axial direction with significantly different mechanical properties in its gap and overlap regions, correlating with its different molecular organizations in these two regions.

Collagen fibrils/aggregates are arranged in different combinations and concentrations in various tissues to provide varying tissue properties. In bone, entire collagen triple helices lie in a parallel, staggered array. 40 nm gaps between the ends of the tropocollagen subunits (approximately equal to the gap region) probably serve as nucleation sites for the deposition of long, hard, fine crystals of the mineral component, which is hydroxylapatite (approximately) Ca10(OH)2(PO4)6. Type I collagen gives bone its tensile strength.

Associated disorders
Collagen-related diseases most commonly arise from genetic defects or nutritional deficiencies that affect the biosynthesis, assembly, posttranslational modification, secretion, or other processes involved in normal collagen production.

In addition to the above-mentioned disorders, excessive deposition of collagen occurs in scleroderma.

Diseases
One thousand mutations have been identified in 12 out of more than 20 types of collagen. These mutations can lead to various diseases at the tissue level.

Osteogenesis imperfecta – Caused by a mutation in type 1 collagen, dominant autosomal disorder, results in weak bones and irregular connective tissue, some cases can be mild while others can be lethal. Mild cases have lowered levels of collagen type 1 while severe cases have structural defects in collagen.

Chondrodysplasias – Skeletal disorder believed to be caused by a mutation in type 2 collagen, further research is being conducted to confirm this.

Ehlers–Danlos syndrome – Thirteen different types of this disorder, which lead to deformities in connective tissue, are known. Some of the rarer types can be lethal, leading to the rupture of arteries. Each syndrome is caused by a different mutation. For example, the vascular type (vEDS) of this disorder is caused by a mutation in collagen type 3.

Alport syndrome – Can be passed on genetically, usually as X-linked dominant, but also as both an autosomal dominant and autosomal recessive disorder, those with the condition have problems with their kidneys and eyes, loss of hearing can also develop during the childhood or adolescent years.

Knobloch syndrome – Caused by a mutation in the COL18A1 gene that codes for the production of collagen XVIII. Patients present with protrusion of the brain tissue and degeneration of the retina; an individual who has family members with the disorder is at an increased risk of developing it themselves since there is a hereditary link.

Characteristics
Collagen is one of the long, fibrous structural proteins whose functions are quite different from those of globular proteins, such as enzymes. Tough bundles of collagen called collagen fibers are a major component of the extracellular matrix that supports most tissues and gives cells structure from the outside, but collagen is also found inside certain cells. Collagen has great tensile strength, and is the main component of fascia, cartilage, ligaments, tendons, bone and skin. Along with elastin and soft keratin, it is responsible for skin strength and elasticity, and its degradation leads to wrinkles that accompany aging. It strengthens blood vessels and plays a role in tissue development. It is present in the cornea and lens of the eye in crystalline form. It may be one of the most abundant proteins in the fossil record, given that it appears to fossilize frequently, even in bones from the Mesozoic and Paleozoic.

Mechanical Properties
Collagen is a complex hierarchical material with mechanical properties that vary significantly across different scales.

On the molecular scale, atomistic and course-grained modeling simulations, as well as numerous experimental methods, have led to several estimates of the Young’s modulus of collagen at the molecular level. Only above a certain strain rate is there a strong relationship between elastic modulus and strain rate, possibly due to the large number of atoms in a collagen molecule. The length of the molecule is also important, where longer molecules have lower tensile strengths than shorter ones due to short molecules having a large proportion of hydrogen bonds being broken and reformed.

On the fibrillar scale, collagen has a lower modulus compared to the molecular scale, and varies depending on geometry, scale of observation, deformation state, and hydration level. By increasing the crosslink density from zero to 3 per molecule, the maximum stress the fibril can support increases from 0.5 GPa to 6 GPa.

Limited tests have been done on the tensile strength of the collagen fiber, but generally it has been shown to have a lower Young’s modulus compared to fibrils.

When studying the mechanical properties of collagen, tendon is often chosen as the ideal material because it is close to a pure and aligned collagen structure. However, at the macro, tissue scale, the vast number of structures that collagen fibers and fibrils can be arranged into results in highly variable properties. For example, tendon has primarily parallel fibers, whereas skin consists of a net of wavy fibers, resulting in a much higher strength and lower ductility in tendon compared to skin. The mechanical properties of collagen at multiple hierarchical levels is given. Collagen is known to be a viscoelastic solid. When the collagen fiber is modeled as two Kelvin-Voigt models in series, each consisting of a spring and a dashpot in parallel, the strain in the fiber can be modeled according to the following equation:

$$\frac{d\epsilon_D}{d\epsilon_T}=\alpha + (\beta - \alpha) exp[-\gamma\frac{\epsilon_T}{\dot{\epsilon_T}}]$$

where α, β, and γ are defined materials properties, εD is fibrillar strain, and εT is total strain.

Uses
Collagen has a wide variety of applications, from food to medical. In the medical industry, it is used in cosmetic surgery and burn surgery. In the food sector, one use example is in casings for sausages.

If collagen is subject to sufficient denaturation, such as by heating, the three tropocollagen strands separate partially or completely into globular domains, containing a different secondary structure to the normal collagen polyproline II (PPII) of random coils. This process describes the formation of gelatin, which is used in many foods, including flavored gelatin desserts. Besides food, gelatin has been used in pharmaceutical, cosmetic, and photography industries. It is also used as a dietary supplement, and has been advertised as a potential remedy against the ageing process.

From the Greek for glue, kolla, the word collagen means "glue producer" and refers to the early process of boiling the skin and sinews of horses and other animals to obtain glue. Collagen adhesive was used by Egyptians about 4,000 years ago, and Native Americans used it in bows about 1,500 years ago. The oldest glue in the world, carbon-dated as more than 8,000 years old, was found to be collagen – used as a protective lining on rope baskets and embroidered fabrics, to hold utensils together, and in crisscross decorations on human skulls. Collagen normally converts to gelatin, but survived due to dry conditions. Animal glues are thermoplastic, softening again upon reheating, so they are still used in making musical instruments such as fine violins and guitars, which may have to be reopened for repairs – an application incompatible with tough, synthetic plastic adhesives, which are permanent. Animal sinews and skins, including leather, have been used to make useful articles for millennia.

Gelatin-resorcinol-formaldehyde glue (and with formaldehyde replaced by less-toxic pentanedial and ethanedial) has been used to repair experimental incisions in rabbit lungs.

Cosmetics
Bovine collagen is widely used in dermal fillers for aesthetic correction of wrinkles and skin aging. Collagen cremes are also widely sold even though collagen cannot penetrate the skin because its fibers are too large. Collagen is a vital protein in skin, hair, nails, and other tissues. Its production decreases with age and factors like sun damage and smoking. Collagen supplements, derived from sources like fish and cattle, are marketed to improve skin, hair, and nails. Studies show some skin benefits, but these supplements often contain other beneficial ingredients, making it unclear if collagen alone is effective. There's minimal evidence supporting collagen's benefits for hair and nails. Overall, the effectiveness of oral collagen supplements is not well-proven, and focusing on a healthy lifestyle and proven skincare methods like sun protection is recommended.

History
The molecular and packing structures of collagen eluded scientists over decades of research. The first evidence that it possesses a regular structure at the molecular level was presented in the mid-1930s. Research then concentrated on the conformation of the collagen monomer, producing several competing models, although correctly dealing with the conformation of each individual peptide chain. The triple-helical "Madras" model, proposed by G. N. Ramachandran in 1955, provided an accurate model of quaternary structure in collagen. This model was supported by further studies of higher resolution in the late 20th century.

The packing structure of collagen has not been defined to the same degree outside of the fibrillar collagen types, although it has been long known to be hexagonal. As with its monomeric structure, several conflicting models propose either that the packing arrangement of collagen molecules is 'sheet-like', or is microfibrillar. The microfibrillar structure of collagen fibrils in tendon, cornea and cartilage was imaged directly by electron microscopy in the late 20th century and early 21st century. The microfibrillar structure of rat tail tendon was modeled as being closest to the observed structure, although it oversimplified the topological progression of neighboring collagen molecules, and so did not predict the correct conformation of the discontinuous D-periodic pentameric arrangement termed microfibril.

title: Collagen