The celebration this year of the 200th anniversary of Darwin's birth and the 150th anniversary of the publication of his Origin of Species has stirred debate over Darwin's legacy. His supporters praise him as a scientist who formulated one of the greatest ideas ever conceived--the theory of evolution. But some people have complained that this exaggerates his importance and ignores the fact that Darwin was largely ignorant of how evolution works, and that subsequent research was required to explain evolutionary mechanisms and overcome Darwin's ignorance. Moreover, Darwin's critics--proponents of creationism and intelligent design theory--have argued that scientific research over the past century has actually refuted Darwin's ideas.
A good contribution to this debate is the PBS television network broadcast last night (December 29) of a two-hour documentary on "What Darwin Never Knew." This is one of the best television documentaries on evolutionary science that I have ever seen. You can view the entire program online at the PBS website, which includes links to related material.
As the title of the documentary indicates, it concedes that Darwin really was remarkably ignorant of exactly how the evolution of species works, particularly at the genetic level. But the documentary also shows how the latest research in evolutionary science works within the basic ideas set forth by Darwin, even as it fills in all the details that Darwin did not know. And thus it denies the claims of the intelligent design creationists that science has refuted Darwin's theory of evolution.
Of course, a two-hour popular science documentary on such a vast area of research has to be simplified and selective. This documentary concentrates on the research in "Evo Devo"--evolutionary developmental biology--particularly as presented in some books by Sean Carroll, an evolutionary biologist at the University of Wisconsin at Madison.
The question is how to explain the remarkable diversity of animal life forms, and particularly, how to explain the diversity of animal species from ancestral species. We might assume that the diverse forms of animal bodies must arise from radically different genes. So, for example, we might think that the wing of a fly and the arm of a human being require radically different genes. In fact, however, the "tool kit genes" for building animal bodies are remarkably similar across all animals. This became apparent when the human genome project showed that human beings have only about 22,000 genes, which is about the same number as other animals.
The differences between animal species come not from differences in their "tool kit genes" but differences in their "genetic switches," which are devices in DNA that tell tool kit genes when, where, and how to act. The gene controlling the formation of a fly's wing is the same as the gene controlling the formation of a human arm. The difference arises during embryonic development as regulatory genes turn the other genes on and off at different times and places in the body.
The beauty of this explanation is that it allows us to explain the origin of new species. Small changes in the timing and pace of these genetic switches can lead to the evolutionary development of new species. So, for example, a fish with fins can evolve into a fish with primitive legs for crawling onto land, when small changes in the genetic switches move from creating fins to creating legs.
This same evolutionary mechanism can explain what makes us uniquely human, with our human capacities for thinking, feeling, and acting. Our human uniqueness depends on the uniqueness of our brains in their size and complexity. The evolution of those brains from smaller and simpler primate brains could arise from evolutionary changes in the genetic regulation of the development of primate brains and nervous systems.
This provides an account of the genetic mechanisms of brain evolution behind what I have called "the emergent evolution of the soul in the brain." The highest human mental capacities--like those for science, religion, and art--arise from human brains that have emerged from primate brain evolution as those brains have passed through ever higher levels of size and organization.
A report on some of the recent research on differences in gene regulatory networks in the brains of chimps and humans can be found here.
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