Is A Revolution Brewing In Evolutionary Theory? - Extended Evolutionary Synthesis (EES).

This is one of the most important pieces you will read this year. Period. 

Full of insights to act on your everyday life (there are tips, it's up-to you to connect the dots). 

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.

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Take the idea that new features acquired by an organism during its life can be passed on to the next generation. This hypothesis was brought to prominence in the early 1800s by the French biologist Jean-Baptiste Lamarck, who used it to explain how species evolved. However, it has long been regarded as discredited by experiment – to the point that the term ‘Lamarckian’ has a derogatory connotation in evolutionary circles, and any researchers expressing sympathy for the idea effectively brand themselves ‘eccentric’. The received wisdom is that parental experiences can’t affect the characters of their offspring.

Except they do. The way that genes are expressed to produce an organism’s phenotype – the actual characteristics it ends up with – is affected by chemicals that attach to them. Everything from diet to air pollution to parental behaviour can influence the addition or removal of these chemical marks, which switches genes on or off. Usually these so-called ‘epigenetic’ attachments are removed during the production of sperm and eggs cells, but it turns out that some escape the resetting process and are passed on to the next generation, along with the genes. This is known as ‘epigenetic inheritance’, and more and more studies are confirming that it really happens.

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Likewise, the diverse, culturally learned foraging traditions of orcas – where different groups specialise in particular types of fish, seals or dolphins – is thought to be driving them to split into several species. Of course, culture reaches its zenith in our own species, where it is now well-established that our cultural habits have been a major source of natural selection on our genes. Dairy farming and milk consumption generated selection for a genetic variant that increased lactase (the enzyme that metabolises dairy products), while starchy agricultural diets favoured increased amylase (the corresponding enzyme that breaks down starch).

All this complexity can’t be reconciled with a strictly genetic currency for adaptive evolution, as many biologists now acknowledge. Rather, it points to an evolutionary process in which genomes (over hundreds to thousands of generations), epigenetic modifications and inherited cultural factors (over several, perhaps tens or hundreds of generations), and parental effects (over single-generation timespans) collectively inform how organisms adapt. These extra-genetic kinds of inheritance give organisms the flexibility to make rapid adjustments to environmental challenges, dragging genetic change in their wake – much like a rowdy pack of dogs.

Despite the excitement of all the new data, it’s unlikely to trigger an evolution revolution for the simple reason that science doesn’t work that way – at least, not evolutionary science. Kuhnian paradigm shifts, like Popper’s critical experiments, are closer to myths than reality. Look back at the history of evolutionary biology, and you will see nothing that resembles a revolution. Even Charles Darwin’s theory of evolution through natural selection took approximately 70 years to become widely accepted by the scientific community, and at the turn of the 20th century was viewed with considerable skepticism. Over the following decades, new ideas appeared, they were critically evaluated by the scientific community, and gradually became integrated with pre-existing knowledge. By and large, evolutionary biology was updated without experiencing great periods of ‘crisis’.

The same holds for the present. Epigenetic inheritance does not disprove genetic inheritance, but shows it to be just one of several mechanisms through which traits are inherited. I know of no biologist who wants to rip up the textbooks, or throw out natural selection. The debate in evolutionary biology concerns whether we want to extend our understanding of the causes of evolution, and whether that changes how we think about the process as a whole. In this respect, what is going on is ‘normal science’.