Bright Eyes

The second of the three studies that I referred to in my post of 11^th June http://clivehumanevo.blogspot.com/2013/06/those-superior-modern-humans.html talks about the apparently larger eyes that Neanderthals had when compared to contemporary modern humans [1]. The sample sizes are miniscule, especially when considering the large geographical regions and time periods covered by the study. Although the authors claim to have studied a sample of 28 Neanderthals and 38 modern humans from the period 27-200 kyr (yes that’s a pooled sample covering 173 thousand years!) some of the comparisons involve much smaller samples. Thus in Table 1 of the paper the comparison of orbital area has sample sizes of 6 for Neanderthals and 10 for modern humans! Anyway, let’s not split hairs and grant the authors the bold claim that Neanderthals had bigger eyes than modern humans. What does this mean?

The first assumption, which may be logical but is an assumption, is the following:

“We have demonstrated that Neanderthals had significantly larger orbits than contemporary AMHs, which, owing to scaling between the components of the visual system, suggests that Neanderthal brains contained significantly larger visual cortices.”

Remember, they don’t know that they had larger visual cortices, they assume it. Fair enough, maybe, but what next? Of course, they start to attack the poor Neanderthals for their inferior cognition:

“In addition, previous suggestions that large Neanderthal brains were associated with their high lean body mass imply that Neanderthal also invested more neural tissue in somatic areas involved in body maintenance and control compared with those of contemporary AMHs.”

Now they’re citing previous suggestions to back up their assumption which is drawn from the conclusion that Neanderthals had bigger eyes than modern humans. The castle is taking shape in the skies above our heads. The story goes on:

“While we cannot partition fossil brains down to the refinement of specific frontal regions, there is at least sufficient evidence from comparative studies of primates to justify using whole brain volumes to estimate cognitive capacities as a first step.”

From this they go to conclude that Neanderthals had reduced cognitive capacities relative to modern humans. To complete the castle that is now flying light years above our heads, they move to the archaeological evidence:

“What little archaeological evidence there is offers support for this: compared with Neanderthals, contemporary Eurasian AMHs had larger [2], more geographically extensive social networks [3,4]. Group size is a convenient index of the cognitive ability to deal with increasing social complexity and may thus evidence more general differences in sociocognitive abilities between these taxa.”

The references cited (my numbers) are worth checking out. Do read them and see what you can find that really supports these claims conclusively. They seem to forget that Neanderthals also show evidence of increased geographical networking in parts of western Europe when climate change opened up their favoured landscapes [5]. So were these extended networks a reflection of modern human improved cognition over Neanderthals or were they simply a reflection of the nature of the landscape they were living in? Pretty important you would agree, as a lot hinges on this for the authors. By the way, don’t lose sight of the papers results which were about eye sizes.

They continue with the presumed differences in geographical networking:

“Such differences may have had profound implications for Neanderthals. First, assuming similar densities, the area group size estimated from standardized endocranial volume covered by the Neanderthals’ extended communities would have been smaller than those of AMHs. Consequently, the Neanderthals’ ability to trade for exotic resources and artefacts would have been reduced, as would their capacity to gain access to foraging areas sufficiently distant to be unaffected by local scarcity. Furthermore, their ability to acquire and conserve innovations may have been limited as a result, and they may have been more vulnerable to demographic fluctuations, causing local population extinctions.”

What??? Are we reading the same paper? Where did all this come from and what does it have to do with larger eyes?

“Whereas AMHs appear to have concentrated neural investment in social adaptations to solve ecological problems, Neanderthals seem to have adopted an alternative strategy that involved enhanced vision coupled with retention of the physical robusticity of H. heidelbergensis, but not superior social cognition.”

Aah, here we go - superior social cognition. They even bring in poor old heidelbergensis, into it now. We have to accept religiously that heidelbergensis existed as a single species and that it was the ancestor of the Neanderthals and not of the modern humans. So the Neanderthals remained physical brutes with good eyes and this prevented them from being as intelligent as modern humans. Now for the piece de resistance

“While the physical response to high latitude conditions adopted by Neanderthals may have been very effective at first, the social response developed by AMHs seems to have eventually won out in the face of the climatic instability that characterized high-latitude Eurasia at this time.”

Back to the high latitude occupation by Neanderthals. Haven’t the authors realised yet that Neanderthals were a mid-latitude taxon that rarely ventured into higher latitudes? I would have thought that they would have been aware of how marginal high latitudes, for example the United Kingdom (see [6]), were for these people. So how can we model the scenario that they had large eyes to deal with poor light and darkness in the latitudes that they hardly ever lived in? I suppose that so long as it serves to put the Neanderthals down and bring our ancestors to the cognitive pinnacle, it is all right. Faith prevails once again.

[1] E. Pearce, C. Stringer, R.I.M. Dunbar (2013). New insights into differences in brain

organization between Neanderthals and anatomically modern humans. Proc. Roy. Soc. B. 280: 20130168

[2] P. Mellars, J.C. French (2011) Tenfold population increase in western Europe at the Neandertal to

modern human transition. Science 333, 623–627.

[3] C. Gamble (1999) The palaeolithic societies of Europe. Cambridge, Cambridge University Press.

[4] P. Mellars (1996) Symbolism, language and the Neanderthal mind. In Modelling the early human

mind (eds P Mellars, KR Gibson). Cambridge, Cambridge University Press.

[5] C. Finlayson (2004). Neanderthals and Modern Humans. An Ecological and Evolutionary Perspective. Cambridge, Cambridge University Press.

[6] C. Stringer (2006). Homo britannicus. London, Allen Lane