Anthropology in the News links to an interesting article on Discovery called Study: Neanderthal Brain Less Troubled. The Discovery article covers a hypothesis put forward in the journal Medical Hypotheses. Before going into the Medical Hypotheses paper, let me quote from the Discovery article:
Although there are conflicting claims about possible Neanderthal creative abilities, no direct evidence supports that this extinct human species or subspecies possessed full-fledged grammatical language. Neanderthals had large brains, but researchers believe their mental skills matured rapidly, closing the door to disorders associated with the cortex.
Modern humans, on the other hand, must take the bad with the good.
“In a nutshell, I feel that the extremely long maturation time of our brains — greater than 20 years — allows them to develop many and various capabilities, such as language and schizophrenia,” H. Lee Seldon, the theory’s author, told Discovery News.
Seldon, a senior lecturer and an expert on health informatics at Monash University in Australia, added, “Also, because of the long maturation time, environmental factors have more time to exert modifying influences on the final outcome.”
He explained that if our brains stopped being modified at age 5, then “we would not have such well-developed language and we would likely not have so much schizophrenia.”
The bit about maturation times and the linguistic and creative abilities of Neanderthals made me somewhat skeptical and I will get back to this below. The Discovery article continues:
The first factor is a sex-linked gene that “steers brain development towards anatomical and functional asymmetry.” A second genetic factor allows us to process fatty acids and produce large quantities of brain membranes, essentially permitting the growth of a big brain.
While Neanderthals probably possessed the first factor and some version of the second, the third genetic determinant appears to be unique to modern humans. Seldon believes it is a gene that influences cortical growth and stretching.
It also delays the end of brain growth until the third decade of life. The developing white matter in the cortex literally winds up expanding parts of our brain like a balloon, according to the hypothesis.
This, in my opinion, is a journalist somewhat misinterpreting what Seldon said. In the Medical Hypotheses article he says:
We summarize these hypotheses together. There is a (sex-linked) genetic factor which steers brain development towards anatomical and functional asymmetry. There is another genetic factor which allows us to process certain fatty acids efficiently and to produce large quantities of brain membranes, especially myelin, which allows our entire brain to grow in both size and functional capacity. There is a third genetic factor which delays the end of brain growth until the third decade of life; this factor allows non-genetic, environmental (”nurture”) factors to exert a greater influence, via balloon-like cortical growth and stretching, and to impose a much greater variability and plasticity on the final outcome of brain maturation. This third factor is the one which is specific to Homo sapiens sapiens. [emphasis mine – afarensis]
To back up this final contention Seldon cites three works: Mithen’s The Singing Neanderthals (which I haven’t read), Stringer and Gamble’s In Search of the Neanderthals (specifically, a discussion of growth rates of Neanderthal incisors) and Ramirez and de Castro’s 2004 Nature article on the subject of the growth of Neanderthal teeth. Hawks covers the subject of what we can learn about Neanderthal development from their teeth – including the Ramirez and de Castro article. The basic point of Hawks’ post is that:
The null hypothesis in this case is that enamel formation times did not differ between fossil and living humans. That hypothesis is not refuted by the available data — and given the wide variation in enamel formation times among living human populations, it seems likely that further sampling of fossil Homo will arrive at the same result. The issue is not sample size for the fossils, in other words, it is the intrinsic variability among living people, which remains unexplained.
The variation among living humans raises a thornier problem, also. The reason why many people are interested in molar enamel deposition is the idea that enamel formation is linked to somatic maturation in general. But the great variability in enamel formation times in recent humans would seem to disprove a strong link between somatic and dental maturation. [emphasis mine – afarensis]
Which effectively undermines Seldon’s argument. Seldon is quite clear that:
The maturation time has not been mentioned explicitly in the balloon model, but it becomes the critical factor in this hypothesis.