Why Does Evolution Produce Such Diversity?

A science writer friend pointed me to a recent “Edge” essay by Freeman Dyson (https://www.edge.org/conversation/freeman_dyson-biological-and-cultural-evolution). Dyson, 95, is a truly great mind, which I am not. Nor an evolutionary biologist. Nevertheless —

Dyson begins with the question: why has evolution produced such a vast diversity of species? If “survival of the fittest” natural selection is the mechanism, shouldn’t we expect each ecological niche to wind up occupied by the one species most perfectly adapted? With others losing out in the competition and disappearing. Thus, in the Amazon rain forest, for example, just one variety of insect rather than thousands; and worldwide, maybe only a few hundred species altogether, rather than the millions actually existing (many with only slight differences). Also, we might expect species slimmed down to efficient essentials, not ongepotchket ones (a Yiddish word for “excessively and unaesthetically decorated.”) These things puzzled Darwin himself.

Darwin worked before we knew anything of genes, Dyson points out. He discusses the contributions of several later people. First is Motoo Kimura with the concept of “genetic drift,” an evolutionary mechanism separate from natural selection. It’s the randomness inherent in gene transmission through sexual reproduction. A given gene’s frequency in a large population will vary less than in a small one, where such random fluctuations will loom larger. Like if you make 1000 coin tosses you’ll always get very close to 500 heads, whereas with only ten tosses you might well get seven heads, a big deviation. So in small populations such genetic drift can drive evolutionary change faster than in a large population where genetic drift is negligible and slower natural selection is the dominant factor. Thus it’s small populations (often ones that get isolated from the larger mass) that most tend to spin off new species.

Dyson combines this idea with cultural evolution which, for humans in particular, is a much bigger factor than biological evolution. Dyson sees genetic drift involved with big local effects, such as the flourishing of ancient Athens or Renaissance Florence.

Then there’s Ursula Goodenough’s idea that mating paradigms, in particular, seem to change faster than other species characteristics. This too makes for rapid evolutionary jumps in genetically isolated populations. Dyson comments: “Nature loves to gamble. Nature thrives by taking risks. She scrambles mating system genes so as to increase the risk that individual parents will fail to find mates. [This] is part of Nature’s plan.” Because it raises the likelihood that parents who do succeed will birth new species.

And then there’s Richard Dawkins and The Selfish Gene. I keep coming back to that book because this — when fully understood — is a very powerful idea indeed.

It tells us that evolution is all about gene replication and nothing else. Thus I take some issue with Dyson’s language anthropomorphizing “Nature” as gambling. He writes as though Nature wants evolution to occur. But it doesn’t have aims. Nor does a gene “want” to make the most copies of itself; it’s simply that one doing so will be more prevalent in a population. That’s what evolution is.

So taking again Goodenough’s point, supposing any given characteristic (here, a mating paradigm) does result in some copies of the relevant gene failing to replicate, if nevertheless in the long run the characteristic means other copies of the same gene will replicate more, then that gene becomes more prevalent. There’s no “gambling” taking place, and no extra points earned if a new species happens to be created. It’s simply the math of the outcome — more copies of the gene.

I also take issue with Dyson’s associating local cultural flourishing with genetic drift. Whatever happened in Fifth Century BC Athens was a purely cultural phenomenon that had nothing to do with changes in Athenians’ genes. While the local gene pool would have differed a (tiny) bit from other human ones, there’s no basis to imagine there was natural selection favoring genes conducive to artistic flourishing, and in any case there would have been insufficient time for such natural selection to play out.

So — returning to the starting question — why all the diversity? While Dyson does point to some mechanistic aspects of evolution militating in that direction, I think there’s a larger and simpler answer. The problem lies in a syllable. “Survival of the fittest” is not quite exactly right; it’s really “survival of the fit.” There’s a big difference. It’s not only the fittest that survive; you don’t have to be the fittest; you just have to be fit. It’s not a winner-take-all competition.

This comports with Dawkins’s selfish gene insight. The genes that continue to exist in an environment are those that have been able to replicate. That doesn’t require being the best at replicating. The best, it is true, will be represented with the most copies, but there will also exist copies of those that are merely okay at replicating; even ones that are lousy, as long as they can replicate at all. The most successful don’t kill off the less successful. Only those totally failing to adapt to their environment die out.

That’s why there are a zillion different varieties of insects in the Amazon rain forest.

But Dyson’s larger point is that for humans, again, cultural evolution outstrips the biological, and this is certainly true. As Dyson notes, language is a huge factor (unique to humans) driving cultural evolution. And while biological evolution does tend toward ever greater diversification, human cultural evolution is actually pushing us in the opposite direction. The degree of human diversity is being collapsed by our cultural evolution — not only our biological diversity, in “races” whose separateness increasingly breaks down, but also cultural diversity, with ancient barriers that separated human groups into combative enclaves breaking down too, so that it is more and more appropriate to speak of a universal humanity.