The central argument of Gelernter’s essay is that random chance is not good enough, even at geologic timescales, to produce the ratchet of escalating complexity we see when we look at living organisms and the fossil record. Most mutations are deleterious and degrade the functioning of the organism; few are useful enough to build on. There hasn’t been enough time for the results we see.
Before getting to that one I want to deal with a subsidiary argument in the essay, that Darwinism is somehow falsified because we don’t observe the the slow and uniform evolution that Darwin posited. But we have actually observed evolution (all the way up to speciation) in bacteria and other organisms with rapid lifespans, and we know the answer to this one.
The rate of evolutionary change varies; it increases when environmental changes increase selective pressures on a species and decreases when their environment is stable. You can watch this happen in a Petri dish, even trigger episodes of rapid evolution in bacteria by introducing novel environmental stressors.
Rate of evolution can also increase when a species enters a new, unexploited environment and promptly radiates into subspecies all expressing slightly different modes of exploitation. Darwin himself spotted this happening among Galapagos finches. An excellent recent book, The 10,000 Year Explosion, observes the same acceleration in humans since the invention of agriculture.
Thus, when we observe punctuated equilibrium (long stretches of stable morphology in species punctuated by rapid changes that are hard to spot in the fossil record) we shouldn’t see this as the kind of ineffable mystery that Gelernter and other opponents of Darwinism want to make of it. Rather, it is a signal about the shape of variability in the adaptive environment – also punctuated.
Even huge punctuation marks like the Cambrian explosion, which Gelernter spends a lot of rhetorical energy trying to make into an insuperable puzzle, fall to this analysis. The fossil record is telling us that something happened at the dawn of the Cambrian that let loose a huge fan of possibilities; adaptive radiation, a period of rapid evolution, promptly followed just as it did for the Galapagos finches.
We don’t know what happened, exactly. It could have been something as simple as the oxygen level in seawater going up. Or maybe there was some key biological invention – better structural material for forming hard body parts with would be one obvious one. Both these things, or several other things, might have happened near enough together in time that the effects can’t be disentangled in the fossil record.
The real point here is that there is nothing special about the Cambrian explosion that demands mechanisms we haven’t observed (not just theorized about, but observed) on much faster timescales. It takes an ignotum per æque ignotum kind of mistake to erect a mystery here, and it’s difficult to imagine a thinker as bright as Dr. Gelernter falling into such a trap … unless he wants to.
But Dr. Gelernter makes an even more basic error when he says “The engine that powers Neo-Darwinian evolution is pure chance and lots of time.” That is wrong, or at any rate leaves out an important co-factor and leads to badly wrong intuitions about the scope of the problem and the timescale required to get the results we see. Down that road one ends up doing silly thought experiments like “How often would a hurricane assemble a 747 from a pile of parts?”
Eric S. Raymond, “Contra Gelernter on Darwin”, Armed and Dangerous, 2019-08-14.
August 10, 2023
QotD: The variable pace of evolution
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As best as I can tell (and I’ve done some digging), there wasn’t a Cambrian Explosion–at least, not in the sense of a bunch of phyla suddenly arising. Genetic data indicate that many of the phyla diverged well before the Cambrian. And we know there was life before that–the Ediacarian, the Vendian, and, most significantly for this discussion, something called the Small Shelly Fauna (paleontologists have a weird sense of what constitutes an appropriate name). The SSF is a bunch of very, very small bits of shell, none big enough to cover a whole organism. What researchers have found is that many of these shells represent partial armor for larger organisms, individual plates or horns or whatever, which disarticulated upon death.
What the Cambrian Explosion represents is not the rise of complex animal life, but rather the rise of hard parts. It’s a point of time a little after the arms race between predator and prey truly got underway. Why then is a very good question that many people have spilled gallons of ink failing to answer. (As for why we don’t find fossils earlier, soft-bodied critters are notoriously rare in the fossil record. Plus, there just isn’t that much Precambrian ancient sea floor available for study.)
This does not mean that I disbelieve the concept of punctuated equilibrium. It’s clearly demonstrated in a fair number of cases (phyletic gradualism is as well; turns out evolution is complicated, especially on geologic timescales). And the arms race between weapons and armor in Animalia likely represents one of those punctuated periods.
Comment by Dinwar — August 10, 2023 @ 07:15
I haven’t done much reading on any of this, so I’ll defer to your clearly deeper scholarship.
Comment by Nicholas — August 10, 2023 @ 10:52