By Paul Theerman, Associate Director, Center for the History of Medicine and Public Health
Charles Darwin was born on this day in 1809. The influence of this “most genial of geniuses,” to quote Stephen Jay Gould, continues.1
What has become more prominent in recent years is the field of evolutionary psychology, which promises a fully naturalistic account of the development of mind as well as body. But Darwin as well as other early 19th-century naturalists held that behavior was an integral part of evolution. Darwin’s precursor, Jean-Baptiste Lamarck, made behavior central to his mechanism for species change. His provided an account of the giraffe, whose incessant and continued stretching of the neck resulted in its slight lengthening, which transferred to the next generation—perhaps through the rush of “gemmules” from the somatic cells to the germ cells, as Darwin surmised in his Lamarckian moments. Over generations, this stretching led to the long-necked animal we have today. Behavior produces bodily change. Darwin posed nothing less, but he proposed the mechanism of natural selection: minute changes in the body or its use, if advantageous to producing offspring that inherit those changes, will over time fix the changes in a population.
Early accounts, and frankly, the way that evolution is often presented in high school classrooms, tend to obscure this. Much late 19th-century work emphasized establishing the fact of evolution, while downplaying the mechanism. Naturalists often focused on comparative anatomy alone, without a behavioral component. For example, one of the more famous “proofs” of evolution is the sequence of horse skeletons that Othniel C. Marsh of Yale set out in 1879—fossil bones put side-by-side.2 Even 20 years ago or so, Gould identified three central disciplines as the cornerstones of modern Darwinism: paleontology, developmental biology, and population genetics3; none of these had much to say about the way that living creatures interact with their environment.
But Darwin did. He served as a naturalist in the field during his four-year trip around the world on H.M.S. Beagle, and he was constantly seeing the living world as a whole. Yes, the specimens he collected eventually made their way to museum drawers, but he always recorded the back story. In his most famous example—the finches of the Galápagos—he was aware of how beak shape was linked to eating patterns, a behavioral characteristic, and how both interacted with the particular environments of each island.
Darwin always explored behavior. Chapter 7 of his masterwork, On the Origin of Species (1859), was devoted to “Instinct.” In later books, notably The Descent of Man and Selection in Relation to Sex (1871) and The Expression of Emotions in Man and Animals (1872), he elaborated his discussion of the evolution of behavior. But in all these books he looked at the “higher” animals, and that could be taken to mean that some element of purposefulness was at work. That is, as with Lamarck’s giraffe, a conscious agent may seem to be choosing a particular evolutionary path, rather than a path emerging by means of natural selection and other mechanisms. So Darwin famously looked at “lower” forms, connecting in them bodily structure, behavior, and environment. He worked on the zoology of barnacles as his major contribution to understanding the Beagle specimens. Above all, he was a botanist, writing books on the movement of plants, and on insectivorous plants, among other efforts. One of his last productions was on earthworms, including “observations on their habits.” His research brought home the three-fold connection of body, behavior, and environment in the evolution of new species, even in creatures that no one could consider conscious or willful.
Here then is the origin of evolutionary psychology. From the tropisms of plants and the habits of worms, to all of living nature, it is not only that our bodies that are evolving and changing in response to nature, but how we use our bodies as well: our conscious minds, but also our perceived instincts, and even our unconscious thoughts and feelings. Evolutionary psychology is built on this.
1. S. J. Gould, “Darwinian Fundamentalism,” The New York Review of Books, June 12, 1997, at http://www.nybooks.com/articles/archives/1997/jun/12/darwinian-fundamentalism/, accessed February 11, 2015.
2. O. C. Marsh, “Polydactyle Horses, Recent and Extinct,” American Journal of Science, 3rd ser. 17 (1879): 499–505.