19 August 2012

Bigger and Smarter Brains: What Makes the Difference?

If you look at brain size across the evolutionary tree, it seems clear that larger brained creatures demonstrate greater intelligence, for the most part, when corrected for body size. What is the evolutionary driving force behind increasing brain size?

Researchers found that protein domain called DUF1220 may explain why humans have bigger brains. Humans have more than 270 copies of DUF1220 in their genome whereas chimpanzees have 125, gorillas have 99 and mice have just one. The number of copies of DUF1220 shows how close an animal may be to humans.

"This research indicates that what drove the evolutionary expansion of the human brain may well be a specific unit within a protein – called a protein domain -- that is far more numerous in humans than other species," said Sikela. _Medical Daily
Article abstract
Wikipedia article on "Protein Domain"
Something has been driving the evolutionary increase in the size and sophistication of the brain. DUF1220 repeats may well be a part of the story, but are not likely to be the entire explanation.

Besides an increase in overall brain size, the relative size of particular brain components have changed. The frontal lobe size in homo sapiens, for example, is thought to be significantly larger than the frontal lobes in homo neanderthals, while the temporal and occipital lobes were larger in the Neanderthal. So although overall brain size was comparable between the two species of homo, actual brain function would likely have been quite different.
Data from Beals, et al, Oregon State University

Even in the modern extended breeding families (races) of homo sapiens sapiens, we find statistical differences in group brain sizes.
The definitive study of race differences in brain size was carried out on approximately 20,000 crania by Professor Kenneth Beals and his colleagues at Oregon State University. Their results for endocranial volume, measured in cubic centimeters for the major races were as follows: North East Asians (Chinese, Japanese and Koreans): 1,416 cm; Europeans: 1,369cm; Native American Indians: 1,366cm; Southeast Asians: 1,332cm; Pacific Islanders: 1,317cm; South Asians: 1,293cm; Sub-Saharan Africans: 1,282cm; Bushmen: 1,270cm; Australian Aborigines: 1,225cm. These brain size differences correspond with intelligence differences derived from IQ tests given by Prof. Richard Lynn, who finds IQs of 105 for North East Asians,100 for Europeans, and so on downwards to 62 for Australian Aborigines and 54 for the Bushmen of the Kalahari desert. _China Daily Forum

Kenneth Beals PDF Download paper

We find that the gross statistical differences in average brain size appear to correlate with the statistical differences in average IQ.

This would not necessarily be the case, given that changes in the organisation of the brain structures and connections themselves could lead to more efficient brain function. The same is true for changes in molecular and genetic efficiency within brain cells -- a smaller brain does not necessarily mean a less functional brain.

At this time it is best to consider these correlations to be curiosities, rather than reflecting any deeper meaning.

But at least we are slowly stumbling upon some of the answers to our questions. As long as we do not allow our science to be perverted by a misplaced sense of political correctness, we should eventually obtain a fairly clear picture of how larger and more intelligent brains evolved.

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