Nothing creates more misunderstanding of the results of scientific research than scientists’ use of metaphors. It is not only the general public that they confuse, but their own understanding of nature that is led astray. The most famous and influential example is Darwin’s invention of the term “natural selection,” which, he wrote in On the Origin of Species,
is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good….
Darwin, quite explicitly, derived this understanding of the motivating force underlying evolution from the actions of plant and animal breeders who consciously choose variant individuals with desirable properties to breed for future generations. “Natural” selection is human selection writ large. But of course, whatever “nature” may be, it is not a sentient creature with a will, and any attempt to understand the actual operation of evolutionary processes must be freed of its metaphorical baggage. Unfortunately, even modern evolutionary biologists, as well as theorists of human social and psychological phenomena who have used organic evolution as a model for general theories of their own subjects, are not always conscious of the dangers of the metaphor. Alfred Russel Wallace, the coinventor of our understanding of evolution, wrote to Darwin in July 1866 warning him that even “intelligent persons” were taking the metaphor literally.
The modern skeletal formulation of evolution by natural selection consists of three principles that provide a purely mechanical basis for evolutionary change, stripped of its metaphorical elements:
(1) The principle of variation: among individuals in a population there is variation in form, physiology, and behavior.
(2) The principle of heredity: offspring resemble their parents more than they resemble unrelated individuals.
(3) The principle of differential reproduction: in a given environment, some forms are more likely to survive and produce more offspring than other forms.
Evolutionary change is then the mechanical consequence of variation in heritable differences between individuals whenever those differences are accompanied by differences in survival and reproduction. The evolution that can occur is limited by the available genetic variation, so in order to explain long-term continued evolution of quite new forms we must also add a fourth principle:
(4) The principle of mutation: new heritable variation is constantly occurring.
The trouble with this outline is that it does not explain the actual forms of life that have evolved. There is an immense amount of biology that is missing. It says nothing about why organisms with the evolved characteristic were more likely to survive or reproduce than those with the original one. Why,…
This is exclusive content for subscribers only.
Try two months of unlimited access to The New York Review for just $1 a month.
Continue reading this article, and thousands more from our complete 55+ year archive, for the low introductory rate of just $1 a month.