Selection's sieve

Nobel prize-winner Manfred Eigen's latest work lays out the case for why evolution by natural selection is a "law of physics"

October 02, 2013
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It’s not hard to find reasons why the new book From Strange Simplicity to Complex Familiarity (OUP, 2013) by 1967 chemistry Nobel laureate Manfred Eigen has barely had any reviews. The title alone is enough to put you off. And once you see the book in all its glory – 700 pages of densely argued, equation-peppered text – you can be forgiven for leaving it to an indefinite "later". It is the kind of book scientists don’t tend to write any more: Eigen’s version of the Principia, basically an immensely long technical paper that doesn’t merely popularize old ideas but advances new ones. (And – gulp – Eigen promises this is just the first of two volumes.)

But it’s a great shame that the book is so forbidding, because it is potentially of huge significance. It lays out the case that Eigen has been building since the 1970s for why evolution by natural selection is a “law of physics” – as inevitable as the formation of atoms or the freezing of water. Here Eigen builds the case much as Gaudí built his cathedral – with baroque embellishments and follies, sparkling (but never boastful) anecdotes about breakfasts with Richard Feynman and chats with Werner Heisenberg, digressions into black hole thermodynamics, information theory and Gödel’s theorem. Eigen – who won his Nobel for work on very fast chemical reactions – is one of the few people who could bring this off, and From Strange Simplicity is among other things a glimpse of a vanishing age and of a thinker determined to ignore disciplinary boundaries.

What can it mean to say that natural selection is a law of physics? Eigen explains that it is not, as evolutionary biologists have tended to assume, something that "just happens" through mutation and competition, but is a fundamental process of any system in which replication by imperfect copying happens under constrained resources. And it isn’t a matter of degree, but is what physicists call a “phase transition”: an abrupt tipping point, like the sudden freezing of water below zero centigrade. Once the rates of mutation and competition reach some critical threshold, a system of reproducing entities must inevitably “crystallize” into a state where natural selection will produce adaptation to the environment.

Why should we care, biologists might ask? We know it happens anyway – what does all this phase transition business bring to the party? But this is to miss the point. Quite aside from the value, in the war against creationism, of framing natural selection as a physical law rather than some provisional contingency, this perspective allows one to frame new questions and to see evolution in a new light.

Take, for example, the issue of neutral selection, in which mutations get fixed into a population not because they are beneficial or adaptive but because they are simply innocuous. Neutral selection is likely to be an important source of biological and genetic diversity, as John Tyler Bonner recently argued in Prospect. It is a well established phenomenon, and yet it has been systematically marginalized by some Neo-Darwinists. Richard Dawkins only recently brought himself grudgingly to admit it any real role in evolution, and as Bonner testified, just talking about neutral selection can get you branded a heretic. Its key proponent, Japanese biologist Motoo Kimura (1924-1994), once asked Eigen if the vilification he received was because of his Asian origin. But the opposition has more of an ideological smell. So elegant does natural selection seem as a sieve of random mutation that it perhaps offends some sensibilities to admit that the sieve is imperfect. If you’ve been going round saying that Darwin’s idea is the best anyone had ever (even though Darwin himself didn’t regard natural selection as exclusive), then you won’t be keen to hear any “Yes buts”. But I’m only guessing here; the fact is that this resistance of smart people to sound science baffles me.

The imperfections of selection’s sieve might hold the key to important aspects of biology, and Eigen’s thesis suggests why. Neutral selection, he says, plays an important role in the phase transition that enables natural selection because it provides a degree of randomness and fluctuation, a kind of shaking-up that prevents the gene pool of a population from getting stuck in a less-than-ideal valley of the evolutionary landscape. In this way it potentially shows that neutral selection, far from compromising natural selection, complements and assists it.

But is Eigen right? It will take far greater minds than mine to decide that, and they will need to read From Strange Simplicity carefully. But I hope they do; if he’s correct, Eigen’s achievement is monumental. Quite apart from anything else, it shows that intellectual and imaginative powers don’t necessarily subside even in your ninth decade.