Biology's theoretical kudzu: The irrepressible illusion of teleology

Abstract

The Argument from Design is a favorite weapon with which to whip evolutionary biologists and give aid and comfort to religious views on the nature of life. The idea that complex structures could not have gotten here just by chance comes in many flavors: teleology (that a structure evolved towards some end objective), vitalism (that living matter contains an immaterial inner guiding force), or animism (that all matter contains such a force). Is somebody in there? Out there? Most biologists would never be caught (sober) endorsing such metaphysical views, and darwinism vigorously defends natural selection as a plausible and sufficient explanation for biological order. Yet ever since Origin of Species was published, prominent biologists, awed by wondrous and exquisite fits between organisms and their environment, have struggled to reconcile or rationalize the manifest appearance of purpose in biological structures with the dead hand of selection. In fact, many of the objections to natural selection raised in Darwin’s time are still in circulation.1 Like kudzu, the Japanese vine that in the southern US creeps relentlessly over everything in its path,2 teleology pops up irrepressibly, even among biologists who rigorously argue that science should have no truck with mystic or immaterial causation. Teleology arises in two basic ways. From a functional point of view, it does not seem too anthropocentric to say that organisms are “designed” to solve problems, from making eyes or lungs, to complex, homeostatic challenges such as transporting oxygen to cells, defending against microbial attack, or flying. In this sense, organisms seem just as functionally designed as airplanes. From an evolutionary point of view, the fossil record can also give the appearance of systematic or directional change in form-following-function. It is not hard to see why we often just barely skirt teleological language. One may smile at Lamarckian notions of striving organisms, but we readily say bats evolved wings “to fly.” A purist might object that this is just rhetoric, but bats fly today because their ancestors strove to fly, and those who did it successfully were passed by selection. Why is the teleology urge so irrepressible? To see the issues, it may be useful to think of a scale of causal effects, like a number line, as shown in Figure 2, that reflects the degree of randomness or determinism that applies to evolutionary change. At one end is 0, or purely chance “causation” with entirely unpredictable outcomes, while at the other is 1, purely deterministic causation with entirely predictable outcome. In the standard way to denote numerical intervals, a square bracket ([or]) indicates an endpoint that is included, while a parenthesis bracket indicates an excluded end point. Where does the evolution of complex traits fall on this line?