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Evolution is Still True

November 30, 2016

This chapter contribution to Scientific American was originally published as “These Truths Are Not Self-Evident—but They’ve Been Firmly Established Over and Over by Scientific Research” (November, 2016). It was co-authored by Michael Shermer, Harriet Hall, Ray Pierrehumbert, Paul Offit, and Seth Shostak.

In a letter to his friend the botanist Joseph Hooker, dated January 14, 1844, Charles Darwin recalled from his voyage around the world in the HMS Beagle: “I was so struck with distribution of Galapagos organisms &c &c…that I determined to collect blindly every sort of fact which cd bear any way on what are species.” After five years at sea and nine years at home thinking about the origin of species Darwin concluded: “At last gleams of light have come, & I am almost convinced, (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable.”

Like confessing a murder. Dramatic words. But it doesn’t take a rocket scientist—or an English naturalist—to understand why a theory on the origin of species by means of natural selection would be so controversial: if new species are created naturally—not supernaturally—what place, then, for God? No wonder Darwin waited 20 years before finally publishing his theory in 1859, and why more than a century and a half later people of some religious faiths still find the theory threatening. But that 150+ years have brought together so much evidence in support of the theory that it would be truly astonishing if it turned out not to be true—on par with doubting the Big Bang origin of the universe or the germ theory of disease. Why? Because of a convergence of evidence from many lines of inquiry.

Cosmologists, for example, reconstruct the history of the universe through a convergence of evidence from astronomy, astrophysics, planetary geology, and physics. Geologists reconstruct the history of the Earth through a convergence of evidence from geology, geophysics, and geochemistry. Archeologists piece together the history of civilization through a convergence of evidence from pollen grains, kitchen middens, potshards, tools, works of art, written sources, and other site-specific artifacts. As a historical science, evolution is confirmed by the fact that so many different lines of evidence converge to this single conclusion. Independent sets of data from geology, paleontology, botany, zoology, herpetology, entomology, biogeography, comparative anatomy and physiology, genetics and population genetics, and many other sciences each point to the conclusion that life evolved.

As well, comparing data from different fields allows us to infer evolutionary relationships. Comparing data from research in population genetics, geography, ecology, archaeology, physical anthropology, and linguistics, for example, scientists discovered that Australian Aborigines are genetically more closely related to southeast Asians than they are to African blacks, which makes sense from an evolutionary perspective because the migration pattern of humans out of Africa led them to Asia and then to Australia.

The consistency of dating techniques for establishing a timeline of the evolution of life on earth also gives us confidence that the theory is true. Uranium Lead, Rubidium Strontium, and Carbon-14, for example, are all reasonably consistent in their determination of the age of rocks and fossils. Even though the ages are given in estimates with well-defined error bars, it is not as if one scientist finds that a fossil hominin is 1.2 million years old while another one finds it is 10,000 years old.

Not only is there consistency in the dates, fossils also show intermediate stages. For example, there are now at least six intermediate fossil stages in the evolution of whales, and more than a dozen intermediate fossil stages since hominids branched off from the great apes six million years ago. And geological strata consistently reveal the same sequence of fossils. Trilobites and mammals are separated by hundreds of millions of years, for example, so finding a fossil horse in the same geological stratum as a trilobite would prove problematic for the theory of evolution, but that has never happened.

Finally, vestigial structures are signs evolutionary history. The cretaceous snake Pachyrhachis problematicus, for example, had small hindlimbs, gone in today’s snakes. Modern whales retain a tiny pelvis for hindlegs that existed in their land mammal ancestors but have disappeared today. Likewise, there are wings on flightless birds and, of course, humans are replete with useless vestigial structures, a distinctive sign of our evolutionary ancestry, such as wisdom teeth, male nipples, body hair, the appendix, and the coccyx.

The influence of the theory of evolution on our culture is so pervasive it can be summed up in a single observation: we live in the age of Darwin. The Darwinian revolution changed both science and culture in at least five ways:

  1. The static creationist model of species as fixed types was replaced with a fluid evolutionary model of species as ever-changing entities.
  2. The theory of top-down intelligent design through a supernatural force was replaced with the theory of bottom-up natural design through natural forces.
  3. The anthropocentric view of humans as special creations above all others was replaced with the view of humans as just another animal species.
  4. The view of life and the cosmos as having design, direction, and purpose from above was replaced with the view of the world as the product of bottom-up design through necessitating laws of nature and contingent events of history.
  5. The view that human nature is infinitely malleable and primarily good waas replaced with the view of a constraining human nature in which we are good and evil.

As the great geneticist and evolutionary theorist Theodosius Dobzhansky famously noted, Nothing in biology makes sense except in the light of evolution.

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