When Darwin, in the third chapter of On the Origin of Species, explored evolution’s ecological context he was not simply laying out a program of research for a future science now called ecology (see previous post). He was responding to anticipated criticisms of his theory of natural selection as the mechanism for evolutionary change that produces the “that perfection of structure and co-adaptation which most justly excites our admiration.”
Recall Darwin’s initial statement of the idea of natural selection. Given the struggle for existence, “any variation, however slight and from whatever cause proceeding, if it is in any degree profitable to an individual of any species in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring” (Darwin 1859, p.61). He goes on, however, to note: “What checks the natural tendency of each species to increase in number is most obscure” (p. 67). And at the end of the chapter, he concludes: “It is good thus to try in our imagination to give any form some advantage over another. Probably in no single instance should we know what to do, so as to succeed. It will convince us of our ignorance on the mutual relations of all organic beings; a conviction as necessary, as it seems to be difficult to acquire” (p. 78).
In short, chapter 3 is a preemptive defence. It was as if he were saying: “There must be such characters, but don’t ask me to show you what they are, to identify what characters of an organism confer fit-ness. There are too many indirect interactions and feedbacks to do this reliably. Instead, we have to just take it as self-evident that there must be such characteristics.” Having pointed to the complexity of ecological dynamics, the challenge remains, 150 years later, of integrating those dynamics into evolutionary theory.
Perhaps researchers will be able to show more cases in nature (as against in the lab.) in which organisms enjoy differential survival and reproductive success because of the effect of some character they possess. But, given the special conditions (see earlier post) that increase the chances of natural selection (carefully construed) serving as an explanation of historical change—and conversely, the complexity of evolution’s ecological context—it may well be that finding many cases will be beyond the data and methodologies available. The issues is not the existence of natural selection in the short term, say, for a generation; I am not positing chance and genetic drift instead of natural selection. The question is whether the generation-by-generation natural selection adds up over time to an outcome that we can, retrospectively, assign to natural selection associated with some specific character that increased in frequency in the population.
If this is a kind of methodological uncertainty principle that evolutionary biologists have to face, I wonder if there is also an ontologically uncertainty principle that organisms face. Each organism makes its living in an ecological context. Some leave more offspring than others. But there are too many indirect interactions and feedbacks for an organism to make its living in ways that humans might call strategic with respect to perpetuating its lineage. For all this, however, organic evolution on earth has taken place in complex ecological contexts for more than 4 billion years.