Domesticated: Evolution in a Man-Made World by Richard C. Francis

Author:Richard C. Francis [Francis, Richard C.]
Language: eng
Format: azw3
Publisher: W. W. Norton & Company
Published: 2015-05-25T04:00:00+00:00

FIGURE 13.7 Cortical neuron, illustrating dendrites, cell body, and axon.

The neotenic development of this part of the brain is not confined to myelination. Gene expression refers to the degree to which a particular gene is actively engaged in the synthesis of the protein that it encodes (see Appendix 12 on page 344). The expression of a particular gene in a particular type of cell—such as a cortical neuron—changes as that cell lineage differentiates from a stem cell. These changes enable scientists to look for heterochrony in gene expression patterns.

A particularly striking case of such heterochrony occurs in the prefrontal cortex. A number of genes involved in neural development exhibit a heterochronic shift in humans relative to chimpanzees, for all of which adult humans resemble juvenile chimpanzees in their expression profiles.83 In the prefrontal cortex, at least, development is slowed (neotenic) relative to chimp development, even while brain growth is accelerated. This neotenic dynamic is not brain-wide, however. In another part of the brain, called the caudate nucleus, there is no evidence of neotenic gene expression.

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