Repost – Fossil feces from an Indiana sinkhole preserve traces of a meat-eater’s meal

Close up of one of the Pipe Creek Sinkhole coprolites showing structures interpreted as hair (A) and a close-up of a mold in the coprolite thought to have been made by a hair (B). From Farlow et al, 2010.

Blogging on Peer-Reviewed ResearchThree years ago, Lawrence Summers, former president of Harvard University, claimed that genetic differences between the sexes led to a "different availability of aptitude at the high end". His widely derided led to his dismissal, but is views are by no means uncommon. In the same year, Paul Irwing and Richard Lynn conducted a review of existing studies on sex differences in intelligence and concluded:

"Different proportions of men and women with high IQs... may go some way to explaining the greater numbers of men achieving distinctions of various kinds for which a high IQ is required, such as chess grandmasters, Fields medallists for mathematics, Nobel prize winners and the like."

ChessSet.jpgIrwing's opinion aside, there clearly is a lack of women in the areas he mentioned. In chess for example, there has never been a single female world champion and just 1% of Grand Masters are women. And as long as that's the case, there will always be people who claim that this disparity is caused by some form of inferiority on the part of the underrepresented sex. Thankfully, there will also always be others keen to find out if those who hold such views are full of it.

Among them is Merim Bilalic from Oxford University. Himself a keen chess player, Bilalic smelled a rat in Irwing's contention that men dominate the higher echelons of chess because of their innate ability. In an elegant new study, he has shown that the performance gap between male and female chess players is caused by nothing more than simple statistics.

Far more men play chess than women and based on that simple fact, you could actually predict the differences we see in chess ability at the highest level. It's a simple statistical fact that the best performers from a large group are probably going to be better than the best performers from a small one. Even if two groups have the same average skill and, importantly, the same range in skill, the most capable individuals will probably come from the larger group.

With this statistical effect in mind, Bilalic wanted to see if the actual sex difference that we see among chess players is any greater than the difference you would rationally expect. Fortunately, there are easy ways of finding out the answer for chess, as opposed to many other intellectual disciplines like science and engineering where success is nigh-impossible to measure objectively.

Every serious player has an objective rating - the Elo rating - that measures their skill based on their results against other players. Bilalic looked at a set of data encompassing all known German players - over 120,000 individuals, of whom 113,000 are men. He directly compared the top 100 players of either gender and used a mathematical model to work out the expected difference in their Elo ratings, given the size of the groups they belong to.

The model revealed that the greater proportion of male chess players accounts for a whopping 96% of the difference in ability between the two genders at the highest level of play. If more women took up chess, you'd see that difference close substantially.

Overall, the women actually performed slightly better than the model predicted and the top three in particular were playing well ahead of expectations. From positions 3 to 73, the men have a small but consistent advantage, wielding a competitive superiority that slightly exceed what statistics would predict. From the 80th pair onwards, the advantage shifts back to the fairer sex. 

Judit-Polgar.jpg Bilalic describes the world's top female player, Judit Polgar, as "a phenomenon, by far the strongest female player the world has ever known [and] the only female player in the top 100". But according to Bilalic's study, the exceptional thing about Polgar is not necessarily that she is an incredible female chess player, but that she is a female chess player at all. Increase female representation in this game and you would probably see many more prodigies rising to the fore.

Bilalic's analysis is a scathing blow against people who claim (and frequently so) that the dominance of men in the world of chess is a sign of their intellectual superiority. His explanation is remarkable for both its simplicity and the fact that hardly anyone has thought about it. Recently, the website ChessBase asked some of the world's best female players to explain the male dominance in their chosen game. None of them mentioned differences in participation rates.

Of course, sceptics could argue that low participation rate is itself caused by the fact that women simply give up chess in greater numbers than men based on some innate disadvantage. As Bilalic says, the argument is "reasonable" but there is no evidence that the drop-out rate is higher in women than men.

In fact, Christopher Chablis and Mark Glickman recently found equal drop-out rates for boys and girls among 600 budding chess players of comparable age, skill and interest. Their study also found that both sexes improve at an matching pace, and they concluded that the success of men at chess's highest tiers is fuelled by the overwhelming majority of boys who enter the game at its lowest levels.

So why are there so few female chess grandmasters? Because fewer women play chess. It's that simple. This overlooked fact accounts for so much of the observable differences that other possible explanations, be they biological, cultural or environmental, are just fighting for scraps at the table.

In science and engineering, where men dominate the top ranks but also have an advantage in numbers, it's likely that the same explanation applies, rather than the innate differences cited by Summers and Irwing. There will always be those who take their position, but it's always nice to have hard data to show how demonstrably daft it is.

Reference: Proc Roy Soc B 10.1098/rspb.2008.1576

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Time and again I have stressed that every fossil bone tells a story, and, in a different way, so do coprolites. Fossilized feces are small snapshots of the lives of prehistoric organisms, often preserving bits of whatever they had been eating, and while coprolites may not get top billing in museum halls, they are among the most pungent reminders that weird and wonderful organisms really did live during the remote past. As reported by paleontologists James Farlow, Karen Chin, Anne Argast, and Sean Poppy in the latest issue of the Journal of Vertebrate Paleontology, two such vestiges of ancient digestive systems have recently been found in Indiana, but what left them is something of a mystery.

Called the Pipe Creek Sinkhole, the site where the coprolites were found dates back to around five million years ago. During that time Indiana was home to a motley assemblage of mammals. As stated by the authors, remains of “insectivores, rodents, hares, peccaries, deerlike ungulates, camelids, rhinoceroses, felids, canids, skunks, and bears” have been found there, but what sort of animal left the scat behind? To find out, the scientists attempted to parse the details of the fossils through thin sections and CT scans.

One of the teeth found in a Pipe Creek Sinkhole coprolite, as seen inside the coprolite (looking at the root of the tooth) and after its removal. From Farlow et al, 2010.

Blogging on Peer-Reviewed ResearchSince the first living things appeared on the planet, the biggest among them have become increasingly bigger. Over 3.6 billion years of evolution, life's maximum size has shot up by 16 orders of magnitude - about 10 quadrillion times - from single cells to the massive sequoias of today (below right). And no matter what people say, size does matter.

Sequoia.jpgThe largest of creatures, from the blue whale to the sauropod dinosaurs, are powerful captors of the imagination, but they are big draws for scientists too. Jonathan Payne from Stamford University is one of them, and together with a large team, he ambitiously set out to understand how the maximum size of living things has evolved throughout the entire history of life on Earth.

Taking each geological era and period in turn, the team scoured the literature for examples of the largest species alive at the time and recorded their size by volume. They also interviewed experts in the field of classification to get their side of the story. Payne's full database is available online and it showed that the massive increase in life's maximum size wasn't a gradual process.

Instead, it happened in two main bursts, which took place in just 20% of the history of life but accounted for 75% of the increase in maximum size. On both occasions, the largest living things became about a million times larger. The first followed the evolution of more complex, compartmentalised cells and the second came after the advent of multi-celled creatures, and both coincided with dramatically rising levels of oxygen in the air. It was a case of environmental changes unlocking pre-existing evolutionary potential.

Twojumps.jpg

Two great steps...

The first jump took place about 1.9 billion years ago, when the first eukaryotic cells came on the scene. Today, these cells make up the bodies of animals, plants and fungi. They all have a nucleus that contain their DNA, along with many other compartments with their own specific functions. It's this internal complexity that sets the eukaryotes apart from prokaryotic cells like bacteria, which lack a nucleus and other such compartments. With its internal division of labour, the eukaryotic cell doesn't have to rely on simple diffusion to carry nutrients into and around its borders, and can therefore afford to be much larger than those following the prokaryotic blueprint.

During this great leap for cell-kind, maximum size shot up by a million times, but stayed pretty much constant for about a billion years. The next big innovation in size happened place between 600 and 450 million years ago, during the Ediacaran, Cambrian and Ordovician Periods. Within a very short span of time, geologically speaking, life on Earth went through an explosion of diversity that saw single-celled species eclipsed by substantially larger multi-celled creatures.

These comparative giants ranged from Dickinsonia, an iconic and enigmatic member of the so-called "Ediacaran fauna", to the orthocones, giant relatives of squid and octopuses that grew up to 9 metres in length. Grypania was a million times larger than the bacteria of the time, but the biggest orthocones were about a million times larger still.

In the 450 million years since the Ordovician, relatively little has happened in the size department. Compared to the largest orthocone, the mighty blue whale is only about 30 times larger and the superlative giant sequoia, the largest living individual organism, is a thousand times larger.

Missing data? 

Grypania.jpgThere will obviously be controversies over any analysis of this scope, but Payne is well aware of them. For example, much of the data to support the first jump in size comes from set of thin, tube-shaped fossils called Grypania spiralis, each just over a centimetre long. Its identity has been hotly debated - some think that the fossils are colonies of bacteria (prokaryotes), but others believe them to be among the earliest known eukaryotes.

Payne believes that the evidence weighs in on the second theory - the fossils are regular in both shape and size and bear signs of an complex internal structure. And even if Grypania was actually a conglomerate of bacteria, there are other large fossilised eukaryotic cells; excluding Grypania would just shift the date of the first size jump forward in time by a few hundred million years. 

Payne also asserts that his database is an accurate reflection of the fossil record and of history itself. For a start, the task of finding the largest species in history was helped by the fact that palaeontologists are an excitable bunch and get even more excited when they discover an unusually large fossil. The upshot is that the names of unusually large fossil species tend to bear Latin or Greek roots that mean "large", "giant" and so on.

Even if the largest species just haven't been found yet (or indeed, if the fossils that have been found were unusually small individuals for their species), it's unlikely that the final result would be greatly affected. The jumps in size that Payne is considering are huge and as he says, "It's unlikely that dinosaurs, whales or cephalopods 10 times the size of the largest known specimens have ever existed."

Payne also considers, and rules out, the possibility that the second size jump is only apparent because later larger animals were better preserved than earlier ones. For a start, the size of fossil tracks and other signs of animal life generally match the size of the fossils themselves. Also, some groups of early animals, like the bizarre anomalocarids, are only very rarely well-preserved but even they have left behind the odd large-bodied remnants. 

All you need is oxygen

It's clear that increases in complexity - from prokaryote to eukaryote, and from single cell to many cells - allowed life to become much bigger. But they weren't necessarily responsible.  Certainly, there seemed to be delays between the big innovations and the size increases they enabled - the first multi-celled fossil eukaryote dates back to 600 million years before the Ediacaran size explosion. Why the gap?

Payne's data can't tell us, but he thinks that it's no coincidence that both size jumps coincide very closely with periods in Earth's history when the concentration of oxygen in the air skyrocketed, from less than a thousandth of modern levels to about 1-10%, and then again to the current standard.

It's a sensible theory - rising oxygen concentrations and body sizes have been linked before and scientists have suggested that increasingly oxygenated atmospheres were triggers for both the origin of eukaryotes, and explosion of animal diversity during the Cambrian Period. Eukaryotes need oxygen to respire and complex multi-celled eukaryotes like the largest animals and plants have an even greater demand for it.

Payne thinks that early species had structural innovations that gave them the potential to get bigger, but increasingly plentiful oxygen was the shot that started the race to become truly enormous. It was the trigger that allowed early life to fulfil the evolutionary potential it already had.

Reference: J. L. Payne, A. G. Boyer, J. H. Brown, S. Finnegan, M. Kowalewski, R. A. Krause, S. K. Lyons, C. R. McClain, D. W. McShea, P. M. Novack-Gottshall, F. A. Smith, J. A. Stempien, S. C. Wang (2008). Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0806314106

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What the paleontologists found was that the coprolites – measuring 50 mm long × 26 mm maximum diameter and 30 long × 26 mm maximum diameter, respectively – were similar in chemical composition to scat produced by meat-eating animals. This was confirmed by remains discovered within one of the specimens. While one coprolite lacked internal detail, the other (INSM 71.3.144.3000) preserved hairs and two teeth from a small carnivorous mammal, perhaps a skunk, indicating that whatever creature produced the scat was itself a carnivore.

The determination that the coprolites were made by a meat-eating animal narrowed down the list of suspects, but the actual identity of the scat-maker proved difficult to ascertain. The enamel of the teeth found in the coprolite was eroded away, something which has been seen in coprolites attributed to crocodiles. The trouble was that no crocodile remains had been found at Pipe Creek Sinkhole. Additionally, while the scats were similar to those made by snapping turtles observed by the scientists in aquaria, the researchers stated that they are doubtful that the scats were left by a turtle due to the relatively large size of the scats and the lack of enamel-eroded teeth in the modern samples for close comparison.

The only other candidates were the large, meat-eating or omnivorous mammals of the site. Of those animals, it seemed most likely that the scats were left by a canid, especially since experimental tests of how dogs consume and digest white-tailed deer jaws have previously confirmed that whole teeth can sometimes make their way into the stomach where their enamel is dissolved before being deposited as scat. While the authors could not rule-out a large turtle as the scat-maker, on the basis of these observations they assigned the coprolites to a wolf-sized canid. Regardless of the identity of what animal left the scat, though, it is wonderful that such signs of ancient life have been preserved, and through using techniques like those employed in this study paleontologists can begin to better resolve the paleobiology of long-dead organisms.

James O. Farlow; Karen Chin; Anne Argast;Sean Poppy (2010). Coprolites from the Pipe Creek Sinkhole (Late Neogene, Grant County, Indiana, U.S.A.) Journal of Verterbrate Paleontology, 30 (3), 959-969 : 10.1080/02724631003762906

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