Posts Tagged ‘Proceedings of the Royal Society’

Neanderthals died out because they could see better than humans

March 13, 2013

Hot on the heels of the theory that Neanderthals died out because they couldn’t adapt from hunting big game to hunting rabbits comes this new theory that they died out because they developed bigger eyes than humans’ in the cold dark Northern latitudes!  The theory goes like this:

Their large eyes led to too much of their brain capacity being used for processing visual information and since more of their brain capacity was also needed to handle the motion of their larger, heavier bodies, this  resulted in less brain capacity being available for cognitive reasoning. They therefore had less brain to deal with other functions like social networking” and had “fewer friends to help them out in times of need”Obviously they then remained culturally trapped in the Stone Age and could not develop written language or Facebook or Agriculture as competing humans eventually did. Apart from a few intrepid and promiscuous Neanderthals who managed to participate in contributing their genes to the human gene pool, all the rest died out.

A novel theory but a little far-fetched!

Eiluned Pearce

This is the theory of  Eiluned Pearce a DPhil student at Oxford and is published in  a paper published today in the Proceedings of the Royal Society B (but where it is beyond a pay wall). A press release has been issued by the University of Oxford.

The only data are measurements of eye sockets in 13 Neanderthal skulls compared to those in 32 human skulls from the same time. All the rest is just conjecture – and then further conjecture based on the original speculation.  It would seem to be a little light on data and a little heavy on conjecture. It is still an interesting conjecture nevertheless.

… Looking at data from 27,000–75,000-year-old fossils, mostly from Europe and the Near East, they compared the skulls of 32 anatomically modern humans and 13 Neanderthals to examine brain size and organisation. In a subset of these fossils, they found that Neanderthals had significantly larger eye sockets, and therefore eyes, than modern humans. 

The researchers calculated the standard size of fossil brains for body mass and visual processing requirements. Once the differences in body and visual system size are taken into account, the researchers were able to compare how much of the brain was left over for other cognitive functions.

Previous research by the Oxford scientists shows that modern humans living at higher latitudes evolved bigger vision areas in the brain to cope with the low light levels. This latest study builds on that research, suggesting that Neanderthals probably had larger eyes than contemporary humans because they evolved in Europe, whereas contemporary humans had only recently emerged from lower latitude Africa.

‘Since Neanderthals evolved at higher latitudes and also have bigger bodies than modern humans, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking,’ explains lead author Eiluned Pearce from the  Institute of Cognitive and Evolutionary Anthropology at the University of Oxford.

‘Smaller social groups might have made Neanderthals less able to cope with the difficulties of their harsh Eurasian environments because they would have had fewer friends to help them out in times of need. Overall, differences in brain organisation and social cognition may go a long way towards explaining why Neanderthals went extinct whereas modern humans survived.’

‘The large brains of Neanderthals have been a source of debate from the time of the first fossil discoveries of this group, but getting any real idea of the “quality” of their brains has been very problematic,’ says Professor Chris Stringer, Research Leader in Human Origins at the Natural History Museum and co-author on the paper. ‘Hence discussion has centred on their material culture and supposed way of life as indirect signs of the level of complexity of their brains in comparison with ours.

‘Our study provides a more direct approach by estimating how much of their brain was allocated to cognitive functions, including the regulation of social group size; a smaller size for the latter would have had implications for their level of social complexity and their ability to create, conserve and build on innovations.’

Professor Robin Dunbar observes: ‘Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks, and are likely also to have resulted in less well developed material culture – which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages.’

The relationship between absolute brain size and higher cognitive abilities has long been controversial, and this new study could explain why Neanderthal culture appears less developed than that of early modern humans, for example in relation to symbolism, ornamentation and art.

The Smithsonian blog writes:

One of the easiest differences to quantify, they found, was the size of the visual cortex—the part of the brain responsible for interpreting visual information. In primates, the volume of this area is roughly proportional to the size of the animal’s eyes, so by measuring the Neanderthals’ eye sockets, they could get a decent approximation of their the visual cortex as well. The Neanderthals, it turns out, had much larger eyes than ancient humans. The researchers speculate that this could be because they evolved exclusively in Europe, which is of higher latitude (and thus has poorer light conditions) than Africa, where H. sapiens evolved.

Along with eyes, Neanderthals had significantly larger bodies than humans, with wider shoulders, thicker bones and a more robust build overall. To account for this difference, the researchers drew upon previous research into the estimated body masses of the skeletons found with these skulls and of other Neanderthals. In primates, the amount of brain capacity devoted to body control is also proportionate to body size, so the scientists were able to calculate roughly how much of the Neanderthals’ brains were assigned to this task.

After correcting for these differences, the research team found that the amount of brain volume left over for other tasks—in other words, the mental capacity not devoted to seeing the world or moving the body—was significantly smaller for Neanderthals than for ancient H. sapiens. Although the average raw brain volumes of the two groups studied were practically identical (1473.84 cubic centimeters for humans versus 1473.46 for Neanderthals), the average “corrected” Neanderthal brain volume was just 1133.98 cubic centimeters, compared to 1332.41 for the humans.

This divergence in mental capacity for higher cognition and social networking, the researcher argue, could have led to the wildly different fates of H. sapiens and Neanderthals. “Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks,” Robin Dunbar, one of the co-authors, said in a press statement. “[They] are likely also to have resulted in less well developed material culture—which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages.”

New insights into differences in brain organization between Neanderthals and anatomically modern humans by Eiluned Pearce, Chris Stringer and R. I. M. Dunbar

Published online March 13, 2013 doi:10.1098/rspb.2013.0168 Proc. R. Soc. B 7 May 2013 vol. 280 no. 1758 20130168 

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Vladimir Nabokov vindicated – about butterflies

January 27, 2011
Polyommatus icarus 5

Polyommatus blue: Image via Wikipedia

Vladimir Nabokov (yes, he of Lolita fame) lived in Cambridge, Massachusets from 1942 to 1948 and while teaching at Wellesley he was curator of lepidoptery at Harvard University’s Museum of Comparative Zoology. His career in entomology was almost as distinguished – but not as lucrative – as his career in literature. In his spare time he composed chess problems. But his work in all these fields was characterised by his “love of detail and contemplation and symmetry”.

In 1945 he published a theory of butterfly evolution claiming that butterflies came to the New World in five waves of migration, through Asia across the Bering Strait into Alaska and then southward through North and then South America (much as humans migrated). Other butterfly experts scoffed at the idea. Nabokov’s theory was not taken seriously until after his death in 1977. Then, in the past decade, gene-sequencing technology finds that Nabokov was right all along and ironically during his life  “Nabokov never accepted that genetics or the counting of chromosomes could be a valid way to distinguish species of insects, and relied on the traditional (for lepidopterists) microscopic comparison of their genitalia”.

Now his theory stands vindicated by work  reported in a new paper in the Proceedings B of the Royal Society:

Phylogeny and palaeoecology of Polyommatus blue butterflies show Beringia was a climate-regulated gateway to the New World by Roger Vila, Charles D. Bell, Richard Macniven, Benjamin Goldman-Huertas, Richard H. Ree, Charles R. Marshall, Zsolt Bálint, Kurt Johnson, Dubi Benyamini and Naomi E. Pierce  doi:10.1098/rspb.2010.2213 Proc. R. Soc. B

Abstract: ….. By integrating molecular phylogeny, historical biogeography and palaeoecology, we test a bold hypothesis proposed by Vladimir Nabokov regarding the origin of Neotropical Polyommatus blue butterflies, and show that Beringia has served as a biological corridor for the dispersal of these insects from Asia into the New World. We present a novel method to estimate ancestral temperature tolerances using distribution range limits of extant organisms, and find that climatic conditions in Beringia acted as a decisive filter in determining which taxa crossed into the New World during five separate invasions over the past 11 Myr. Our results reveal a marked effect of the Miocene–Pleistocene global cooling, and demonstrate that palaeoclimatic conditions left a strong signal on the ecology of present-day taxa in the New World. …..

From Neatorama:

There were several plausible hypotheses for how the butterflies might have evolved. They might have evolved in the Amazon, with the rising Andes fragmenting their populations. If that were true, the species would be closely related to one another.

But that is not what Dr. Pierce found. Instead, she and her colleagues found that the New World species shared a common ancestor that lived about 10 million years ago. But many New World species were more closely related to Old World butterflies than to their neighbors. Dr. Pierce and her colleagues concluded that five waves of butterflies came from Asia to the New World — just as Nabokov had speculated.

“By God, he got every one right,” Dr. Pierce said. “I couldn’t get over it — I was blown away.”

Dr. Pierce and her colleagues also investigated Nabokov’s idea that the butterflies had come over the Bering Strait. The land surrounding the strait was relatively warm 10 million years ago, and has been chilling steadily ever since. Dr. Pierce and her colleagues found that the first lineage of Polyommatus blues that made the journey could survive a temperature range that matched the Bering climate of 10 million years ago. The lineages that came later are more cold-hardy, each with a temperature range matching the falling temperatures.

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