1 of 3
Adaptationism and Optimality
edited by Steven Hecht Orzack and Elliott Sober
Cambridge Univ. Press, 2001
416 pp.; $28, paper
According to Darwinism, biological evolution proceeds without discernible plan or purpose. To be sure, biological evolution produces things that look planned or purposed. But what underlies Darwinian evolution ultimately is a blind mechanical process—the Darwinian mechanism of natural selection.
Darwin himself argued that natural selection, though not capable of purposive action, is nonetheless capable of producing the appearance of purpose in nature. Indeed, he ascribed remarkable skill to natural selection. In The Origin of Species he wrote: "Natural selection picks out with unerring skill the best varieties." Darwin elaborated:
Natural selection 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; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life.
In this way natural selection accomplishes all of biology's design work without being an actual designer. Natural selection is not a watchmaker per se but a blind watchmaker, to use Richard Dawkins' apt phrase. Natural selection does not operate with actual plans or purposes. It does not look into the future and deliberate about what biological structures and functions might be worth innovating. Rather, natural selection is an opportunist that takes advantage of useful variations that arise as organisms reproduce.
For this reason, even though the word "design" appears in the biological literature, one is more apt to find reference to "adaptation," especially within the field of evolutionary biology. Natural selection takes advantage of useful variations. What makes them useful is that they help fit or adapt organisms better to their environments. Monkeys climbing on trees and in danger of falling find it useful to have a tail that grasps branches. Natural selection will tend to favor such tails, which were not "designed" in the strict sense of the word but rather are adaptations. So runs the Darwinian story.
In Adaptationism and Optimality, Steven Orzack (president and research scientist at the Fresh Pond Research Institute in Cambridge, Massachusetts) and Elliott Sober (an influential philosopher of science who has published widely on Darwinian matters) want both to test and to flesh out this story. They want to test it because there is some dispute within the evolutionary biology community whether particular traits are adaptations and thus principally the result of natural selection or whether some other factors might be involved. Further, they want to flesh out this story by providing an analytically precise account of what it means for a trait to be an adaptation.
On both counts their project is commendable. It is all too easy to attribute an organism's traits to natural selection. Since an organism with this or that trait is surviving and reproducing, may we not conclude that the trait contributes to the organism's benefit? Once that assumption is made, the next step is to spin a tale about how it does so—a task that may require considerable ingenuity. Alternatively, if the trait is plainly hampering the organism, one can argue that it is vestigial—that in time past it did benefit the organism, but that now it no longer does, and that natural selection is in the process of removing the maladaptive trait (perhaps even by driving the organism extinct).
share this page
RSS Feed
