John Dupré continues our special 50th issue series

Although developmental systems theory (DST) is generally traced to psychologist Susan Oyama’s influential 1985 book, The Ontogeny of Information, and seminal earlier papers by the biologist Richard Lewontin, it has really caught hold among philosophers of biology and philosophically-minded biologists in the last decade. (A search for the phrase on the ISI web of Knowledge gives 58 results, of which 51 are in the 21st century.) DST is a perspective on evolution critical of the over-emphasis on genetic change that still dominates much discussion of the topic. Like the more mainstream biological movement of evolutionary developmental biology (“evo-devo”) it emphasises the importance of development, as against the blackboxing of development implicit in an understanding of evolution as fundamentally a genetic phenomenon. But it goes further than evo-devo, in proposing the developmental system as the fundamental unit of analysis for evolutionary theory.

Rather than a series of genomes, DST sees evolution as a series of life-cycles. In propagating a new life-cycle a parental organism provides a range of developmental resources. These developmental resources constitute part of the developmental system, which may also include environmental resources recruited by the developing organism itself. Though genes are of course among the essential resources, these also include additional biological material (minimally that in the egg cell), the environment provided by the maternal uterus and, for many species including of course our own, provision of food, shelter, information about the environment, and training in interacting with it. The still widely cited definition of evolution as change in gene frequency should be rejected: evolution may involve changes in any developmental resource, provided only that there is some mechanism by which the change is transmitted to subsequent generations. This, as well as grounding important criticisms of popular gene-centred versions of evolutionary psychology, also offers theoretical support for the experimental research tradition of developmental psychobiology, an important though generally less visible alternative.

DST provides the context for understanding a range of biological ideas that have been developing rapidly in the last decade. Central among these is epigenetics. Epigenetics explores the ways that the behaviour of genes, far from being fully determined by the unchanging structure of the DNA molecules, is constantly modulated by external influences, some of which involve more or less stable modifications to the molecule itself. Although the proximate causes are molecular, chemical entities (which may, crucially, be transmitted in the maternal cytoplasm), relevant causal chains can begin with influences outside the organism. So, for example, experimental work has revealed epigenetically modulated changes in the brains of rat pups consequent on mothering behaviour. Since female pups exposed to appropriate mothering will, as a result of these changes, be more disposed to provide this kind of care to their own pups, there is a mechanism of intergenerational transmission. The example reveals possible trajectories for evolutionary change quite independent of changes in the DNA sequence.

Another important topic is symbiosis. Interest here has been fuelled by developments in microbiology, an area of science that has responded explosively to the growing sophistication of molecular methods. It has emerged that microbes are typically highly sociable organisms, not only with their own kind, but also with quite different organisms. All complex organisms, including ourselves, live in symbiotic relationships with microbes. For example, 90% of the cells in a human body are microbes. What has only recently been appreciated is that these microbes are not merely opportunistic immigrants to a convenient environment, but are rather essential contributors to the functioning of the whole human system. In experimental animals and very probably in us, they influence the expression of “host” genes during development, indicating that they are in fact part of the developmental system. A plausible rationale is provided for the notion that children suffer by being inadequately exposed to dirt.

Finally, there is an obvious connection with an important recent theoretical perspective on evolution: niche construction. This develops the insight, prefigured in Darwin’s work, that organisms do not merely adapt to an environmental niche that is provided by nature, but often, perhaps typically, construct in part the niche to which they are adapted. The point is of fundamental importance to human evolution. For the vast infrastructure of schools, hospitals, supermarkets, and so on that support modern human life are both essential parts of the developmental system in which humans grow, and the niche constructed by humans in part to promote the growth of their offspring.

Understanding of human nature has suffered from hasty application of neo-Darwinian ideas. DST is a vital part of an emerging set of ideas that offers important new insights into what we are and how we got here.

Further reading
Cycles of Contingency. Developmental Systems and Evolution, S. Oyama, P.E. Griffiths and R.D. Gray (MIT Press, 2001).

John Dupré is professor of philosophy of science at the University of Exeter and author of Darwin’s Legacy: What Evolution Means Today (Oxford University Press)

Read all fifty ideas and more in the special 50th issue of tpm