Evolution
In the first instance, the theory of evolution claimed that the various species of living things have a natural rather than a divine origin. These species evolve through random changes that occur in their members, though these changes themselves are not per se inheritable, as the French biologist Jean-Baptiste Lamarck had supposed. In one way or another, such changes can influence an animal’s chances of survival and of reproducing itself. In this way, a process of natural selection takes place from which the human species itself emerged.
As a theory of human nature, evolution had a humbling effect on the pride associated with claims that humans held a privileged status among living things. Yet it did not have any direct bearing on the traditionally held distinction between the body and the mind. It was, in fact, hard to imagine what further influence evolution could have in the human case without appealing to changes that in one way or another would be of a mental character. All of this made evolutionary thought more of a threat to religious beliefs than to philosophical accounts of human nature, because the latter did not require any special assumptions regarding how the human species was formed.
Yet when evolutionary theory joined forces with genetics, as it did in the 20th century, it became possible to point to something within the human body—genes—that accounted for the heritable traits and mutations that occur in humans and in all living things. The inference has been widely drawn that human genetic makeup determines matters that had previously been thought to be controlled by rational thought and moral decision making. Now that the human genome has been completely sequenced, it may appear as though all the categories that have defined moral personality have been displaced by DNA, the organic chemical in which genetic information is encoded.
This at least has been the popular understanding of these developments, and apparently that of some professional students of these matters as well. Some of the latter have gone so far as to claim that the only meaningful possibility of human self-transcendence is that of passing one’s own genes into the next generation. These developments have been carried further by the emergence of evolutionary psychology, which equates the mind with the brain and views it as progressively modified by the same kinds of evolutionary changes that occur in all living things.