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posted by takyon on Monday February 05 2018, @11:55PM   Printer-friendly
from the Lamarck-wasn't-(all)-wrong dept.

Is evolutionary science due for a major overhaul – or is talk of 'revolution' misguided?

When researchers at Emory University in Atlanta trained mice to fear the smell of almonds (by pairing it with electric shocks), they found [DOI: 10.1038/nn.3594] [DX], 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. 

Let's return to the almond-fearing mice. The inheritance of an epigenetic mark transmitted in the sperm is what led the mice's offspring to acquire an inherited fear. In 2011, another extraordinary study [open, DOI: 10.1016/j.cell.2011.10.042] [DX] reported that worms responded to exposure to a nasty virus by producing virus-silencing factors – chemicals that shut down the virus – but, remarkably, subsequent generations epigenetically inherited these chemicals via regulatory molecules (known as 'small RNAs'). There are now hundreds of such studies [DOI: 10.1098/rsfs.2016.0135] [DX], many published in the most prominent and prestigious journals. Biologists dispute whether epigenetic inheritance is truly Lamarckian or only superficially resembles it, but there is no getting away from the fact that the inheritance of acquired characteristics really does happen.

By Popper's reasoning, a single experimental demonstration of epigenetic inheritance – like a single black sheep – should suffice to convince evolutionary biologists that it's possible. Yet, by and large, evolutionary biologists have not rushed to change their theories. Rather, as Lakatos anticipated, we have come up with auxiliary hypotheses that allow us to retain our long-held beliefs (ie, that inheritance is pretty much explained by the transmission of genes across generations). These include the ideas that epigenetic inheritance is rare, that it does not affect functionally important traits, that it is under genetic control, and that it is too unstable to underpin the spread of traits through selection.

Unfortunately for the traditionalists, none of these attempts to bracket epigenetic inheritance look credible. It is now known to be widespread in nature [DOI: 10.1098/rsfs.2016.0135] [DX], with more and more examples appearing every day. It affects [DOI: 10.1126/science.1248127] [DX] functionally important features such as fruit size, flowering time and root growth in plants – and while only a fraction of epigenetic variants are adaptive, that's no less true of genetic variation, so it's hardly grounds for dismissal. In some systems where rates of epigenetic change have been measured carefully, such as the plant Arabidopsis thaliana, the pace has been found [open, DOI: 10.1073/pnas.1424254112] [DX] to be low enough to be selected and lead to cumulative evolution. Mathematical models have shown [open, DOI: 10.1086/660911] [DX] that systems with epigenetic inheritance evolve differently from those solely reliant on genetic inheritance – for instance, selection on epigenetic marks can cause changes in gene frequencies. There's no longer any doubt that epigenetic inheritance pushes us to think about evolution in a different way.

Is Lamarck laughing from the grave?


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  • (Score: 4, Insightful) by c0lo on Tuesday February 06 2018, @02:35AM

    by c0lo (156) Subscriber Badge on Tuesday February 06 2018, @02:35AM (#633595) Journal

    Well this could have been traced to dna damage of the gametes, or fetus.

    Or just epigenetic changes passed to the next generation. Like, genes are still there, but some of them are inhibited, some others with enhanced expression.

    Since the current Dutch generations don't show those changes anymore, one is strongly persuaded towards epigenetic changes rather than DNA damage.

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