Kevin Laland writes:

When researchers at Emory University in Atlanta trained mice to fear the smell of almonds (by pairing it with electric shocks), they found, to their consternation, that both the children and grandchildren of these mice were spontaneously afraid of the same smell. That is not supposed to happen. Generations of schoolchildren have been taught that the inheritance of acquired characteristics is impossible. A mouse should not be born with something its parents have learned during their lifetimes, any more than a mouse that loses its tail in an accident should give birth to tailless mice.

If you are not a biologist, you’d be forgiven for being confused about the state of evolutionary science. Modern evolutionary biology dates back to a synthesis that emerged around the 1940s-60s, which married Charles Darwin’s mechanism of natural selection with Gregor Mendel’s discoveries of how genes are inherited. The traditional, and still dominant, view is that adaptations – from the human brain to the peacock’s tail – are fully and satisfactorily explained by natural selection (and subsequent inheritance). Yet as novel ideas flood in from genomics, epigenetics and developmental biology, most evolutionists agree that their field is in flux. Much of the data implies that evolution is more complex than we once assumed.

Some evolutionary biologists, myself included, are calling for a broader characterisation of evolutionary theory, known as the extended evolutionary synthesis (EES). A central issue is whether what happens to organisms during their lifetime – their development – can play important and previously unanticipated roles in evolution. The orthodox view has been that developmental processes are largely irrelevant to evolution, but the EES views them as pivotal. Protagonists with authoritative credentials square up on both sides of this debate, with big-shot professors at Ivy League universities and members of national academies going head-to-head over the mechanisms of evolution. Some people are even starting to wonder if a revolution is on the cards.

In his book On Human Nature (1978), the evolutionary biologist Edward O Wilson claimed that human culture is held on a genetic leash. The metaphor was contentious for two reasons. First, as we’ll see, it’s no less true that culture holds genes on a leash. Second, while there must be a genetic propensity for cultural learning, few cultural differences can be explained by underlying genetic differences.

Nonetheless, the phrase has explanatory potential. Imagine a dog-walker (the genes) struggling to retain control of a brawny mastiff (human culture). The pair’s trajectory (the pathway of evolution) reflects the outcome of the struggle. Now imagine the same dog-walker struggling with multiple dogs, on leashes of varied lengths, with each dog tugging in different directions. All these tugs represent the influence of developmental factors, including epigenetics, antibodies and hormones passed on by parents, as well as the ecological legacies and culture they bequeath. [Continue reading…]