Is evolution predictable? This is one of the Big Questions, as much philosophy as it is biology and no less important for not really having an answer. You’re probably familiar with it as the rhetorical peg for countless talks on convergent evolution; I’ve already seen two this year to use it, and it’s only February. So it’s somewhat surprising that Jonathan Losos’ new book Improbable Destinies is, to the best of my knowledge, the first broadly framed exploration of the topic for a general audience. If I’m right about this, it was probably worth the wait–Destinies is pleasingly readable, and a mostly deft blend of science with explanations of why we should care about it.
The bulk of the book is a well-curated catalog of case studies spanning Anolis lizards in the Bahamas to E. coli in incubators in Michigan. These examples broadly trend from the descriptive to the experimental, from vertebrates to the microbes. Avoiding the missteps of other scientist-memoir-cum-manifestos, Losos strikes a judicious balance between focusing on his own work (which he of course knows best) and the work of others; and between the obscure (Russel 1982??) and the canonical (Schluter et al. 1985). In a few instances, big names became real people: the history behind Endler’s guppy research is delightful, and I was pleased to learn Rowan Barrett is a backcountry skier. The glue that holds these chapters together, though, is the way in which the broad themes of evolutionary biology are tied together by the yin and yang of the historical accident and the deterministic force of selection. From morphological novelty in the platypus to the pace of diversification, Losos makes a compelling argument that most research topics can be viewed through the lens of convergent evolution. If you’re anything like me, you’re left with the suspicion that you might be unknowingly studying it, too.
His obvious affection for anoles and fieldwork mishaps aside, Losos’ greatest enthusiasm–and the book’s greatest strength–is reserved for discussions of the experimental method in evolutionary biology. Destinies’ early pages sneak in a discussion of evolution as a historical science, and as an inductive (versus deductive) one. He returns to the topic with depth and elegance in one of the book’s concluding chapters, a discussion of the implications of competing definitions of the word “contingency” on our understanding of evolution based on the work of the philosopher of science John Beatty. Throughout, his preoccupation with explaining how we know what we know elevates occasionally rushed gee-whiz science anecdote to something more important. This will not be surprising to anyone familiar to Losos’ academic work (I’ve linked to his 2003 paper on the inferential limits of the phylogenetic comparative method on here more than once before, which I keep on my desk as a perpetual reminder not to make lazy assumptions from phylogenetic trees). But it is refreshing, and to me gets at one of the reasons scientists should read popular science books: namely, to find a clarity of thought and purpose that is easily lost in the methodological swamps of our increasingly specialized subdisciplines.
This is a review, and I have my quibbles. Losos strikes a conversational tone throughout, displaying an inordinate fondness for dad jokes, puns, and goofy alliteration in the early chapters of the book. Like so many anoles on Cuba, this tendency reaches its greatest adaptive radiation in a discussion of parallel evolution of small body size in island mammoths. (Behold and marvel at the following examples, which are dropped in the span of three sentences: “Crete didn’t have a monopoly on puny pachyderms. Indeed, tiny tuskers evolved on many islands…Three lessons can be drawn from this profusion of paltry proboscideans.”) More seriously, nonscientist readers might be confused by the cursory discussions of genetics and heredity, and occasionally undefined jargon; I lack the necessary distance from the source material to tell.
Ultimately, the largest thing that’s missing is a discussion of the topic’s existential stakes that lives up to book’s lofty subtitle and the portentous Mützel artwork on the cover. Losos bookends Destinies with the question of whether another humanoid species could evolve from different historical circumstances–from dinosaurs, or from extraterrestrials. It’s an engaging way to drive home the point that we’re as much a product of these processes as anything else. But while elsewhere in the book Losos’ careful both-sidesism reads as the measured perspective of an especially thoughtful scientist, here it feels a bit like a punt. Were we inevitable, or an accident? What would it mean for us and our place in the universe either way? There’s another book here waiting to be written, though I can’t fault Losos for avoiding it in favor of his own (very good) one–these are treacherous waters indeed. I just look forward to reading it someday.