In the light of evolution VI: Brain and behavior

Abstract

In On the Origin of Species by Means of Natural Selection (1859), Darwin (1) barely mentioned the brain. Only in The Descent of Man, and Selection in Relation to Sex (2), published in 1871, did Darwin emphasize that the human nervous system, like any other organ system, must have evolved. Even so, Darwin himself wrote little on the brain. Instead, Darwin asked his good friend T. H. Huxley to write a chapter for the second edition of The Descent of Man, and Selection in Relation to Sex that dealt specifically with human brain evolution. In this chapter, Huxley laid to rest Richard Owen’s earlier argument that human brains are outliers among mammalian brains. Instead, Huxley argued that our brains resemble the brains of other apes in all fundamental respects. He even downplayed the greater size of human brains, noting that brain size is quite variable among humans. Importantly, Huxley did not deny that our brains must somehow differ from the brains of other apes, for he could see no other way to explain our unique cognitive capacities, most notably language. However, Huxley postulated that the differences that set our brains apart are not apparent in gross dissections (3⇓⇓⇓–7). ### Box 1. In the light of evolution. In 1973, Dobzhansky (45) penned a short commentary titled “Nothing in biology makes sense except in the light of evolution.” Most scientists agree that evolution provides the unifying framework for interpreting biological phenomena that otherwise can often seem unrelated and perhaps unintelligible. Given the central position of evolutionary thought in biology, it is sadly ironic that evolutionary perspectives outside the sciences have often been neglected, misunderstood, or purposefully misrepresented. Biodiversity—the genetic variety of life—is an exuberant product of the evolutionary past, a vast human-supportive resource (aesthetic, intellectual, and material) of the … [↵][1]1To whom correspondence should be addressed. E-mail: fjayala{at}uci.edu. [1]: #xref-corresp-1-1