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For many years the philosophy of science was largely the philosophy of physics and to a lesser extent chemistry. The hegemony of physics among the sciences has been greatly diminished by the increased profile of biology and related disciplines. Biological research now attracts vast public and private funding, meanwhile biology has been the subject of increased attention by philosophers in recent years. As with the philosophy of the other special sciences, philosophical problems in the philosophy of biology fall into two broad types: on the one hand there are the specific conceptual, methodological and metaphysical issues that arise when we analyse particular theories; on the other hand there are the general problems of philosophy of science about explanation, natural kinds, the nature of theories and so on, applied to the biological domain. The philosophy of biology has become a mature discipline in the last few decades and there now exist a number of specialist journals dedicated to it, such as Studies in History and Philosophy of the Biological and Biomedical Sciences, and Biology and Philosophy.
How do we explain the fact that animals and plants often seem to possess just the right characteristics for the environment and lifestyle in which they live; in other words, how do we explain the fact that so many living organisms seem to be so well adapted for survival and reproduction? Since Darwin the traditional answer appealing to God’s benevolent design has been supplanted by the appeal to ‘natural selection’ and the ‘survival of the fittest’. Darwin allowed that other forces than natural selection can influence the course of evolution; current debate focuses on the relative importance of adaptation and such other forces, and the degree to which biologists are entitled to take the existence of a trait as evidence that it must be an adaptation.
The idea of natural selection is that traits persist because they confer an advantage on their possessors. But what types of entity should we regard as the possessor of such traits? In other words, did, say, the opposable thumb evolve because of the advantages it conferred on individual organisms, groups of organism, a whole species of organisms, or because it helped some genes to reproduce themselves in the next generation of their hosts? This is the units of selection problem.
It is natural to think that evolutionary biology tells us what certain traits are for; for example, the stripes on a zebra are there for camouflage. But this way of putting things is teleological, in other words it makes reference to goals and purposes, and yet since the seventeenth century teleology has been excised from the physical sciences. If there is no intelligent creator how can we use intentional notions like design, purpose and so on in biology. Natural selection offers a way of legitimising such talk: to say that some trait has a certain function, is just to say that it has persisted because the function it performs confers an evolutionary advantage upon its bearer. But how are we to pick out the function of something from all the things it does which are intuitively irrelevant for survival and reproduction? For example, the heart pumps blood but it also makes a noise; how can we distinguish functions from side-effects in a principled way? Theorists are divided between two broad accounts of function, namely the historical and ahistorical.
Species are a fundamental unit in the classification of life; organisms are grouped into species, species into genera, genera into families, families into orders, orders into classes, classes into phyla, and phyla into kingdoms. Species are also fundamental units in the description of evolutionary history. It is an important question whether there is a single ‘species level’ of organisation across all organisms which can play both the classificatory and evolutionary roles, or whether the species identified in different parts of biology for different purposes may sometimes only partially overlap. A related issue is whether species are examples of what philosophers call natural kinds.
If all organisms are ultimately driven to survive and reproduce why are there so many examples in both animals and humans of seemingly selfish behaviour. The obvious answer is that such behaviour may not benefit individual animals but it does benefit the groups and species to which they belong. Yet this is merely to restate the problem for the question is precisely why individual organisms should behave in ways which are sometimes positively disadvantageous to them, in order to help others in their group or species. Altruistic behaviour is open to exploitation and so one might expect it to have been selected against rather than for, yet one need only think of ants and bees to be reminded how prevalent it is.
Sociolobiology is a research programme which aims to find evolutionary explanations for human social behaviour. Evolutionary psychology is the study of psychology in the light of evolutionary theory. The application of evolutionary theory to human behaviour becomes particularly controversial when it is claimed that normative questions in ethics, say concerning altruism, and epistemology, say concerning rationality, can be reformulated and resolved with the scientific study of our evolutionary history.