Big brains, baldness and a hybrid

A while back, I read a very interesting scientific paper published in the prestigious science journal Cell. The authors of the paper studied the differences in the DNA between humans, primates and rodents, all mammals but species with significantly different behaviour. The authors found that the genetic changes needed for humans to have their bigger brains, and for those brains to work, include an extensive and specialised set of genetic alterations. What's more, humans have gained all those required genetic changes in a very short time, genetically speaking.

What especially caught my eye in this paper was how often the word 'remarkable' was used. Scientific papers are almost always dry, sober reports, their authors do not want to sound emotional and flighty, and so it is illuminating that the authors saying remarkable in two particular paragraphs. Here they are:

“It has long been noted that brains of various extant and extinct primates display remarkable variation in size, organization, and behavioral output (Noback and Montagna, 1970; Armstrong and Falk, 1982; Byrne and Whiten, 1988; Matsuzawa, 2001). This is particularly true for the evolutionary lineage leading from ancestral primates to humans, in which the increase in brain size and complexity was remarkably rapid and persistent throughout the lineage (Jerison, 1973; Walker et al., 1983).” Page 1.

“It is remarkable that 17 out of the 24 primate-fast outliers [rare or exceptional genetic changes] are linked to the regulation of either brain size or behavior.”

The third ‘remarkable’ is of special significance, for it touches upon a very strange story.

According to the official line, based on Darwin's Theory of Evolution, homo sapiens (us) naturally evolved from Homo Erectus in about one million years. They in turn evolved from Homo Erectus in about one million years. Homo Erectus had a brain capacity of 850 cm³ and Homo Habilis had a brain capacity of 600 cm³. Chimpanzees have a brain capacity of up to 500 cm³. Humans, the last in line of these species, have a brain capacity of roughly 1400 cm³.

This sounds, at first glance, to be a reasonable progress of development. Bigger brains enable tool use, group coordination, planning etc. The only problem is that the odds of gaining the required genetic changes to have these big brains through natural selection, in the time described, are vanishingly small.