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Jonathan B. Losos

IMPROBABLE DESTINIES

How Predictable is Evolution?


Book review by Anthony Campbell. The review is licensed under a Creative Commons Licence.
An important controversy in evolutionary biology concerns the inevitability or otherwise of the appearance of humans. According to Steven J. Gould, if the tape of life could be rerun from the beginning it is very unlikely that anything resembling humans would appear. But Simon Conway Morris disagrees. He and those who think like him hold that something very similar to us was pretty well bound to arise, and similar organisms would evolve on any other planets that support complex life (though these are likely to be rare). So who is right? This is the question that Losos tackles in his new book.

The main evidence that Conway Morris cites to support his thesis comes from convergent evolution. This refers to the independent evolution of similar features in different lineages; for example, birds, bats, pterosaurs, and insects all evolved the ability to fly although in different ways. Conway Morris's book, Life's Solution: Inevitable Humans in a Lonely Universe, provides a huge number of examples of convergence.

This is certainly impressive. But the cases he cites are all retrospective; they describe convergences that have developed over very long periods. This is how we normally think of evolution, as a slow process taking thousands or millions of years. But what Losos writes about is modern experiments showing that in some circumstances evolution can occur extremely rapidly—in fact, over just a few generations.

Losos is himself involved in this kind of research and describes his own experience, but there is also a lot of information about the work of others. The book is written in a very accessible style and will hold the interest of anyone who has wondered about the question it addresses. In part this is because Losos uses almost a detective-story method; he doesn't tell us his own view at the outset but works up to it in his final section (so I won't give it away here).

The book is in three parts. Part 1 is a survey of examples of convergence. Losos agrees with Conway Morris that these often astonishing cases present a challenge to Gould's view. But there is also counter-evidence in the form of animals and plants that have evolved only once and are therefore unique. A prime example is the Platypus, with its duck-like bill, poisonous spurs, and egg-laying reproduction. Nothing like it ever appeared outside Australia, yet there are habitats in other continents where it might have flourished if it had evolved there. Then there is Madagascar, which produced, among many other curiosities now extinct, vegetarian crocodiles and the elephant bird that was ten feet tall and half a ton in weight.

At the end of his historical survey Losos finds the case for inevitability to be suggestive but not conclusive.

Conway Morris and his colleagues are to be commended for bringing convergent evolution to the forefront. We all knew about convergence as a neat trick of natural history, a striking example of the power of natural selection. But Conway Morris and company have made clear that evolutionary duplication is much more common than we realized. We now recognize that it's a frequent occurrence in the natural world, with examples all around us. Still, it's far from ubiquitous. Seemingly just as often, maybe more often, species living in similar environments don't adapt convergently.
Part 2 is where Losos reports on experiments in evolution done by himself and many others. A commonly used method is to isolate populations of various species such as fish or lizards (Losos's favourite subjects) in a new habitat, perhaps accompanied by a predator, and see how they evolve.

The fish studied by Losos were in remote jungle areas of Trinidad; research lasted over years or even decades and was sometimes quite dangerous owing to snakes and other hazards. All this is described entertainingly but the experiments evidently required a huge amount of dedication.

Losos's lizard experiments were done on small rocky islands in the Caribbean. They were usually less risky for the experimenters but they had their own hazards, notably hurricanes, which ended several promising experiments prematurely. Other researchers have worked in more artificial environments, either in the laboratory or outdoors, in specially engineered settings.

Evolution often happened with astonishing rapidity in these setups, over just a few generations. But this is obviously very different from the huge natural time scale of biological evolution over millions of years and generations. Yet it is possible to approach such time scales by using bacteria, which produce new generations much more quickly—every 20 minutes for some species. Work done in this way by Rich Lenski has yielded fascinating results, including a totally unexpected mutation allowing the bacteria to use citrate, something never seen in this species before.

[The new mutation] left only one conclusion: this single population that had lived in flasks for fourteen years in the Lenski Lab had made a major evolutionary leap. Somehow, through the right combination of mutations and natural selection, the population had evolved an adaptation that, as far as anyone knows, this species had never been able to produce in millions of years of its evolution in the wild.
At one time Lenski's work seemed to be a strong confirmation of the predictability of evolution, but now Lenski himself thinks that this needs to be modified.

The book is written with a lot of humour and contains plenty of background anecdotal information, yet you are reading real science, not gossip. At the end of Part 3 I felt I had been given a convincing answer to the Gould–Conway controversy. The excellent drawings by Marlin Peterson add to the pleasure of reading, even in the Kindle version.

23-09-2017


%T Improbable Destinies
%S How Predictable is Evolution?
%A Jonathan B. Losos
%I Penuin
%C London
%D 2017
%K evolution
%O illustrated by Marlin Peterson
%O kindle version; downloaded from www.amazon.co.uk, 2017
New Reviews | Titles | Authors | Subjects