Adaptation

I

Introduction

Adaptation, apparently designed feature of an organism, that has evolved by natural selection over numerous generations to solve the problems of survival and reproduction faced by the organism’s ancestors.

II

The Nature of Adaptations

Intuitively, adaptations are familiar to us as those striking aspects of the living world that, as Darwin aptly put it, “most justly excite our admiration”. Organisms and all their parts have a pervasive air of purpose about them, a highly organized complexity, a precision and efficiency, an ingenious utility.

A favourite example of Darwin’s was the woodpecker’s beak and tongue, finely engineered for excavating insects buried in tree barks; and there is the no less impressive engineering of brain and behaviour, ensuring that the hard-won prey is to the woodpecker’s taste. There are many other examples, such as the warning calls of vervet monkeys, differentiated according to whether the predator is a python, martial eagle, or leopard—and to which the hearers respond differentially by looking down, looking up, or running to trees; the gentle mottling of a camouflaged insect contrasted with the vibrant warning colours of a closely related species that mimics the livery of a noxious animal; the female sage grouse, which fastidiously rejects suitors that bear visible parasite scars; the scoops on the penis of a damselfly, which remove rival sperm before the owner deposits his own; the air conditioning of termite mounds, maintaining a constant temperature in spite of the savannah’s extremes of climate; and orchids luring pollinators by their likeness to female bees, clamping their pollen on the deceived visitor’s back.

III

How Adaptations Come About: Natural Selection

Darwin viewed adaptation as the central problem that any theory of evolution had to solve. And his theory of natural selection triumphantly solved it, for it is through natural selection that adaptations come about—gradually, cumulatively, incrementally honed by selective forces in changing environments over millions of years.

A

Genes and Phenotypes

Natural selection works on genes and the properties that they give rise to. Genes do not present themselves naked to the scrutiny of natural selection. They present tails, fur, muscles, shells; they present the ability to run fast, to be well camouflaged, to attract a mate, to build a good nest. These properties are called phenotypes or the phenotypic effects of genes. Differences in genes give rise to differences in phenotypic effects. Natural selection acts on genes via phenotypes: genes are perpetuated insofar as they give rise to phenotypes that have selective advantages over competing phenotypes. Thus genes come to be represented in successive generations in proportion to the selective value of their phenotypic effects—that is, by virtue of the design features, the adaptations, to which they give rise.

So adaptations can be thought of as phenotypes that promote the replication of the genes that give rise to those phenotypes—as mechanisms that solve design problems and thereby enhance the replication of the genes that give rise to those mechanisms.