As one of several intellectuals who wrote about evolution before Darwin, time has not been kind to the French naturalist Jean-Baptiste Lamarck (1744-1829). Reviled during his lifetime by the influential Cuvier, after his death he became best remembered, and ultimately ridiculed, for the idea that characters acquired during an organism’s lifetime are passed on to its offspring. With the rise of the modern field of epigenetics, some of his ideas are making a comeback, albeit modified and adapted for the 21st Century. Palaeontologist and astrobiologist Peter Ward would even like to go so far as to restore some honour to his name and consider epigenetics a neo-Lamarckian process.
Lamarck’s Revenge starts with a useful intellectual history that drives home the point that the ideas of Lamarck and Darwin were very much a product of what was intellectually fashionable at the time, and what was still unknown. So, while Darwin was heavily influenced by Lyell’s idea of uniformitarianism (introduced in my review of Cataclysms: A New Geology for the Twenty-First Century) and Malthus’s ideas on overpopulation (see my review of his An Essay on the Principle of Population: The 1803 Edition), the discovery of genetics and DNA were still many decades away. But once these had been made, they eclipsed Lamarck’s idea of the inheritance of acquired characters. Until, some now argue, epigenetics came into the picture.
Epigenetics is the study of changes in an organism caused by changes in gene expression rather than in the genetic code itself. So, up- or down-regulation of gene activity rather than mutations. Chiefly, there are three mechanisms: methylation (the addition of methyl groups to DNA), modification of histones (the proteins that give DNA its larger macrostructure, coiling its double helices around spool-like proteins), and RNA interference (the silencing of gene activity by a small piece of RNA).
These epigenetic changes are apparently heritable, though I was left with many questions as to how. Some explanation is offered for methylation but it is unclear whether we don’t know about the rest, or whether Ward assumes this known on the part of the reader. If methylation is removed from DNA when egg and sperm cells are formed, what happens to epigenetic marks during regular cell division? How, as Ward asserts, are epigenetic modifications turned into permanent changes to DNA a number of generations down the line? And what is the link or the difference between the ability of epigenetics to produce variable phenotypes and the classic mechanism of phenotypic plasticity? He mentions Carey’s The Epigenetics Revolution: How Modern Biology is Rewriting Our Understanding of Genetics, Disease and Inheritance as a landmark book summarizing basic processes from a chemical and biological viewpoint, so I have ordered this next. And a quick skim of Duncan et al’s 2014 open-access review paper in the Journal of Experimental Zoology Part B: Molecular and Developmental Evolution already provides leads to answers.
“It is ironic that Ward, having just lamented that there is so much confused usage of the term epigenetics [invokes] lateral gene transfer. Err, that’s not epigenetics.”
Having introduced epigenetics, the rest of the book addresses a variety of topics, trying to argue the importance of epigenetic inheritance for each of these. It is ironic that Ward, having just lamented that there is so much confused usage of the term epigenetics, and having established that this process by definition leaves the DNA sequence unchanged, then goes and immediately muddles the waters. He examines the origin of life and the blossoming of life after mass extinctions through an epigenetic lens by invoking lateral gene transfer. Err, that’s not epigenetics.
Now, don’t get me wrong: this large-scale exchange of chunks of DNA by viruses and bacteria is very influential (see my review of The Tangled Tree: A Radical New History of Life, and yes, lateral and horizontal gene transfer are two names for the same process). It provides a good mechanism for Stephen Jay Gould’s idea of punctuated equilibrium, the idea that evolution consists of long periods of relative stasis, punctuated by short bursts of rapid change (see Punctuated Equilibrium). And it could very well have been a driver of the rapid diversification of life after mass extinctions such as the Cambrian Explosion (see The Cambrian Explosion: The Construction of Animal Biodiversity). Ward tries to defend his choice by saying that it is not the slow-and-steady process of random mutation that Darwin proposed, therefore it is Lamarckian, therefore epigenetic. That is presenting a strict, almost caricatured interpretation of Darwin’s ideas that few evolutionary biologists still adhere to nowadays (see for example Extended Heredity: A New Understanding of Inheritance and Evolution). More importantly, this is macro-mutation, plain and simple. It is a wholesale change to a DNA sequence, and therefore by definition not epigenetic.
Ward repeats this in his final chapter on the gene-editing technology CRISPR (see also my reviews of A Crack in Creation: The New Power to Control Evolution and Modern Prometheus: Editing the Human Genome with CRISPR-Cas9). He seems intent on scaring readers with bleak scenarios of human supersoldiers and parallels to the horrors of the atomic bomb that followed the discovery of nuclear fission. Meanwhile, he ignores that, for all of CRISPR’s power and utility, many human traits are complex and polygenic (influenced by numerous genes of small effect, see for example my review of Blueprint: How DNA Makes Us Who We Are), which makes them little accessible to CRISPR editing. And again, since CRISPR allows direct alteration of the genetic code it is by definition not epigenetic.
“his idea that epigenetics coexists with classic Darwinian selection […] is attractive”
Is this just semantics? I think not. In what is supposed to be a popular science book on epigenetics this will escape the attention of many readers and leave them with the wrong ideas. Ward also misses the truly interesting bits. He briefly mentions that we have recovered signs of methylation on ancient DNA (i.e. DNA recovered from archaeological remains). Now that is revolutionary! And his idea that epigenetics coexists with classic Darwinian selection – the former operating in times of upheaval when rapid adaptation is called for, the latter in times of relative peace when mutation proceeds steadily – is attractive. It could do much to solve the conundrum of “missing links” and the lack of transitional forms in the fossil record, a favourite argument of creationists. Maybe the fossil record isn’t so incomplete after all.
The remaining chapters invoke the idea that all sorts of stresses could have played, or are playing, a role in human evolution by inducing epigenetic changes through DNA methylation. Ward poses many interesting questions. What was the epigenetic impact of experiencing the stresses of war or pandemics, or the loss of loved ones to these? What of the epigenetic impact of chemical signals released by the gut’s microbiome during periods of famine? And what of our current exposure to toxic chemicals, many of which are evolutionary completely novel? Ward here mixes research with assertion in short sections that often feel like they could have been further developed, and seems keen to quickly conclude that epigenetics must be important. His citing of both primary research and secondary sources such as blogs, TED talks or news reports seems questionable and sometimes unnecessary. Why cite news items instead of the paper being reported on?
Those familiar with epigenetics will appreciate some of the flashes of insight in this book, but the limited explanation of how epigenetic inheritance actually works, the confusion caused by prominently including non-epigenetic mechanisms, and the firm assertions when so much research is still in its infancy make it hard to recommend this book to novice readers. As my first entry into this topic I found it to be a hit-and-miss affair and will search out Carey’s book next.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
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