This review originally appeared in The Washington Independent Review of Books on 30 August 2017.
For those of us who aren’t evolutionary biologists, it may come as a surprise to learn that there is such a field as experimental evolution. (Is now the time to admit not knowing about evolutionary biologists, either?)
This and other surprises both fascinating and a bit discomfiting await the non-expert reader of Jonathan Losos’ Improbable Destinies: Fate, Chance, and the Future of Evolution, a thoroughly accessible analysis of whether evolution is one big crapshoot or rather mundanely predictable. No spoilers here, but the evidence presented on both sides makes for some thought-provoking reading.
Losos made his early bona fides as the Lizard Guy, doing lots of undergraduate, graduate, and later fieldwork with anoles in the Bahamas (he agrees that it’s a tough life but somebody’s got to live it).
He is now a professor of biology and director of the Losos Laboratory at Harvard, and Curator of Herpetology at Harvard’s Museum of Comparative Zoology. Being a university professor, he publishes often in scholarly journals, but also writes for a popular audience in places like the New York Times.
The great proponent of evolution as an unpredictable and unrepeatable series of happenstance is Stephen Jay Gould, who posited that you could hit the rewind button on evolution and replay it infinitely and never get the same outcome twice.
This is a concept known as “contingency,” in which any outcome is dependent upon the tiniest factors all lining up in exactly the right sequence. Yet much of the evolutionary record — as well as plenty of extant species, including those anoles — illustrates the concept of convergent evolution, where similar environmental pressures in disparate locales give rise to virtually identical evolutionary adaptations.
(Personally, I am crushed to learn that I missed out on the “Shetland pony-sized” pigmy elephants that apparently evolved independently on islands around the world, “some recent enough to have coexisted with modern humans: Malta, Corsica, St. Paul off the coast of Alaska; Flores, where they lived with Komodo dragons; even the Channel Islands off the coast of Southern California.” What?)
On the other hand, there are plenty of examples of once-and-done species that evolved a single time and remain unique, including most of New Zealand’s fauna (where mammals never evolved), a good chunk of Australia’s, and, lest we forget, us.
The Gould Camp would say we’re a one-in-infinity outcome, while others, like Dale Russell, theorize that, even if that asteroid had missed Earth and mammals had never gotten their evolutionary shot, it’s completely plausible that evolution and selection would have favored dinosaurs that were big-brained and bipedal, eventually resulting in — voila! — the dinosauroid.
Evolutionary biologists are probing the “contingency vs. determinism” theories through both lab and field experiments to assess evolution’s general predictability. One of them, Rich Lenski, took Gould’s “replay the tape” challenge literally, establishing a long-term evolutionary experiment (LTEE) with E. coli that started in 1988 and continues today through tens of thousands of generations.
By starting with a single parent strain and growing 12 separate colonies under identical conditions for years, Lenski was seeing whether they all behaved identically. The findings over time from this and other LTEEs offer some surprises but generally show significant predictability.
While many of us tend to think of evolution as an eons-long process, we also intuitively understand that rapid genetic changes give rise to such organisms as antibiotic-resistant bacteria and pesticide-resistant insects.
Fast changes happen in larger creatures, too. Losos introduces us to many examples of field-based experiments in evolution that demonstrate just how quickly natural selection works to change the make-up of a given population.
His long-running work with anoles had already documented examples of consistently convergent evolution in which nearly identical lizards evolved on different islands to fill nearly identical ecological niches.
His later work took that a step farther and put genetically similar anoles on tiny, lizard-free islands to see what would happen. When the populations did not get wiped off the map by hurricanes, they evolved in ways the research team found to be fairly predictable.
In Trinidad, experimental evolution fieldwork with guppies demonstrated how predation pressure affects coloration. Again and again, experiments showed that, under low predation, male guppies quickly became more brightly colored, apparently something that held appeal for female guppies. Under high predation, issues of attractiveness were thrown out the evolutionary window as duller colors helped males to survive long enough to mate. (Better dull but alive than sexy but dead, as evolutionary biologists like to say.)
The speed with which these changes occur — within a few years or even just a few seasons — is pretty stunning, but it’s also a little worrisome how the researchers choose to jigger around with wildlife, introducing species where they weren’t, including adding predators into the mix where they previously hadn’t been.
Losos discusses this somewhat, arguing that the introductions mimic what often happens naturally. Still, it sure feels like we’ve seen this “Man Monkeys with Nature: Bad Outcomes Ensue” movie before.
So why do we care about evolutionary predictability, anyway? As Losos points out in discussing diseases such as cystic fibrosis, any level of predictability is better than none if it gives us hint in advance about how these diseases might shape-shift in the face of drug therapies.
All this goes to presume that a reader is willing to face the concept of evolution in the first place. Losos notes that the National Science Foundation asks evolutionary biologists, when writing up the description of their funded grants for public release, to avoid the “E” word so as not to trigger an ugly backlash.
Indeed, it seems that however it is we humans came about, we still haven’t evolved a consistently open mind or a thicker skin.