In the fourth video in the “Twelve days of evolution” series produced by PBS and “It’s okay to be smart,” Joe Hanson, Ph.D. (Biology) tells a whopper about the evolution of the eye. Stop me if you’ve heard this one before:
Computer simulations have replayed the process in just 350,000 generations, showing simple light patches can evolve into camera-like eyes in tiny, adaptive steps, 1,829 to be precise. Nature took a little longer than that, but genes, biochemistry, fossils, and anatomy all tell the same story. Eyes are pretty easy to evolve. So easy that nature has done it independently 50 to 100 times. That kind of complexity, rather than overthrowing Darwin’s theory, is proof of its power.
Back in 2013, I debunked these claims in my post, Could the eye have evolved by natural selection in a geological blink?.
Briefly:
(i) the model of eye evolution referred to in the video, which was developed in 1994 by Dr. Dan-Eric Nilsson and Dr. Susanne Pelger of Lund University in Sweden, was not a computer simulation, as Dr. David Berlinski has previously pointed out;
(ii) I contacted Professor Nilsson back in 2013, and asked him about the 1994 paper he co-authored with Susanne Pelger, and he admitted that the model which he and Pelger had developed was actually an intelligently guided evolutionary sequence, and that the variations in the model, while gradualistic, were not random;
(iii) the figure of 350,000 generations (actually 363,992 generations, to be precise) was a “nice round number,” which appears to have been deliberately chosen in order to provide Darwin’s theory with some good publicity. Had Nilsson and Pelger been less conservative in their “pessimistic estimate,” their calculations would actually have shown that the eye could have evolved in just 3,650 years, which is roughly equivalent to the time that has elapsed since the death of Pharaoh Tutankhamun. But of course, nobody – not even the man in the street – would believe a fantastic claim like that;
(iv) Nilsson and Pelger explicitly acknowledge in the final paragraph of their paper that their 364,000-year estimate was never meant to be a realistic one, and applies to a hypothetical situation in which “selection for eye geometry and optical structures imposed the only limit”;
(v) Nilsson and Pelger’s estimate isn’t anatomically realistic: it leaves out the brain. Most lens eyes would be useless to their bearers without advanced neural processing;
(vi) Nilsson and Pelger readily admit in their paper that their 364,000-year estimate deliberately confines its attention to one organism, and ignores changes occurring in other species, and in the organism’s environment;
(vii) Nilsson and Pelger’s estimate isn’t computationally realistic: it assumes a very smooth fitness landscape, as Dov Rhodes demonstrated in a 2007 physics thesis which addressed their 1994 paper;
(viii) Nilsson and Pelger’s estimate isn’t genetically plausible: it says nothing about the genetic changes required to produce an eye;
(ix) Nilsson and Pelger’s estimate isn’t plausible at the embryological level.The authors fail to address the question of how the changes required to produce an eye would have impacted the embryonic development of organisms that were evolving this eye. Organisms’ developmental pathways are extremely fragile, especially in the early stages;
(x) Nilsson and Pelger’s model isn’t plausible at the biochemical level: it fails to address the biochemical changes that must have occurred in the eye, during its evolution from a light-sensitive spot to a vertebrate eye, citing only a brief reference to the literature on the subject. In fact, the various proteins that were involved in the evolution of the eye are not readily inter-convertible. It is by no means a foregone conclusion that the alpha crystallins present in the crystalline lens of the vertebrate eye could ever have naturally evolved into beta-gamma crystallins, which belong to an entirely different family. Likewise, it is doubtful whether the three families of crystallins (J1, J2, and J3) found in the eyes of cubozoan jellyfish could have developed from a common molecule without intelligent guidance.
Summing up my findings, I wrote:
I conclude, then, that the 364,000-year estimate proposed by Nilsson and Pelger for the evolution of the eye is not a biologically realistic one: it applies only to a “toy” world where one structure can simply transform itself by imperceptible degrees into another. But without this estimate, the whole foundation for the Darwinian claim that the evolution of the vertebrate eye from a light-sensitive spot is a plausible occurrence collapses. All we are left with is theoretical possibility. And that, as we have seen, isn’t enough to make Darwin’s theory of evolution by natural selection a proper scientific theory.
Professor Jerry Coyne has some further critical comments in his post on the “12 Days of Evolution” video:
The video’s claim that eyes have evolved independently 50-100 times is dubious. It depends on what you mean by “eyes,” for eyes from insects to humans have co-opted on the same controlling gene (Pax6), so at least that bit isn’t independent. If you mean “the structure of the eye”, then yes, those structures have evolved independently several times, but I don’t think it’s 50-100.
What do readers think? Comments are welcome.