From “Tiny Genetic Variations Led to Big Changes in the Evolving Human Brain”
(ScienceDaily, May 30, 2012) , we learn,
In a study published in the May 31 issue of the journal Nature, Yale researchers found that a small, simple change in the mammalian genome was critical to the evolution of the corticospinal neural circuits. This circuitry directly connects the cerebral cortex, the conscious part of the human brain, with the brainstem and the spinal cord to make possible the fine, skilled movements necessary for functions such as tool use and speech. The evolutionary mechanisms that drive the formation of the corticospinal circuit, which is a mammalian-specific advance, had remained largely mysterious.
For the record, birds are also capable of fine, skilled movements; it’s not a mammalian thing (though the authors may be on to something in thinking that the circuit they describe plays a role in mammals – though not uniquely in humans, as the release’s title implies):
Most mammalian genomes contain approximately 22,000 protein-encoding genes. The critical drivers of evolution and development, however, are thought to reside in the non-coding portions of the genome that regulate when and where genes are active. These so-called cis-regulatory elements control the activation of genes that carry out the formation of basic body plans in all organisms.
Non-coding regions? Better known, to Darwinists, as ”junk DNA” whose sheer uselessness proves their theory.
The whole thing is probably way more complex than this, and doesn’t really tell us much about the evolution of the explicitly human brain, or of human speech. Which, incidentally, is principally driven by intellect, not specific circuits. Consider all the alternative communication methods humans have developed over the millennia (smoke signals, drum language, American sign language, palm signs for the deaf blind). The critical change was actually having something to communicate that requires a human type language.