Evolution Icon Evolution

Eyes in a Twinkling? 

Richard Dawkins

In December 1991, Richard Dawkins gave a lecture in London arguing that natural selection can produce complex and seemingly improbable features such as eyes by an accumulation of small, incremental steps. Starting at 31:50, Dawkins began talking about Swedish biologist Dan-Eric Nilsson, who (Dawkins claimed) had demonstrated how eyes could evolve “in very small steps, on his computer.”

From 32:26–33:11 in the lecture, Dawkins described how Nilsson

assumed that each step, which means each mutation, caused only a one percent change in the size of something, like, say, the steepness of a cup. He also devised a way of measuring the efficiency of an eye. He did this by telling the computer to measure various things about the eye that it had just drawn itself. And then the computer worked out, using the rules of physics, how good an image that eye would be capable of producing. And the question was, with those rules built into it, would there be a smooth gradient of improvement, starting out with a flat retina and ending with a proper eye like ours? And you’ve guessed it, the answer is yes.

On a screen behind Dawkins flashed a series of ten two-dimensional drawings, starting with a flat layer of tissue and ending with a camera-like eye. 

But it wasn’t until April 1994 that Nilsson published anything on this issue. At that time, he and his colleague Suzanne Pelger published a paper in the Proceedings of the Royal Society of London titled “A pessimistic estimate of the time required for an eye to evolve.”

Nilsson and Pelger’s paper included a series of eight two-dimensional drawings to represent eye evolution. (The eight published drawings were different from the ten drawings used by Dawkins in his 1991 lecture.) The first drawing was of a flat patch of light-sensing cells sandwiched between a transparent protective layer and a layer of dark pigment. The last was of a camera eye, and the other six drawings showed a stepwise progression from the first to the last. 

According to Nilsson and Pelger, they measured four parameters in each of their drawings: the length of straight structures, the arc length of curved structures, and the height and width of the two-dimensional cup formed by the rounding up of these structures. Assuming that each of these four parameters could change 1 percent at a time, they estimated the number of steps it would take for the first of their drawings to become the second, the second to become the third, and so on. Then they added up the numbers they had obtained and concluded that “1829 steps of 1% are needed for the entire model sequence.” Combining this with some assumptions about variability, heritability, selection, and generation time, Nilsson and Pelger calculated that a camera eye could evolve in about 364,000 years. They concluded, “It is obvious that the eye was never a real threat to Darwin’s theory of evolution.” 

A Computer Model?

The same week that Nilsson and Pelger’s paper appeared, Dawkins published in Nature a congratulatory commentary titled “The eye in a twinkling.” Dawkins reported that Nilsson had produced a “computer model” that was allowed to “deform itself at random” and preserved only those deformations that improved on what went before. According to Dawkins, the “quick and decisive” outcome was a camera-like eye.

But Nilsson and Pelger’s paper did not say anything about a “computer model.” Much less did the paper claim to describe a model that was allowed to “deform itself at random.” The authors had simply drawn some figures to represent hypothetical intermediates between simple and complex eyes. Then they took measurements of the figures they themselves had drawn and performed some calculations on them.

A computer model is a program that attempts to simulate as realistically as possible something that has happened or might happen in the future. In the case of the eye, such a program would have started with measurements of the three straight lines in the flat patch and applied a formula predicting how those lines would deform under random variation and natural selection. Then it would project the results on the computer screen. Nilsson and Pelger had done nothing of the sort.

Nilsson and Pelger’s calculations gave the illusion that they had quantified a real evolutionary process, when all they had done was measure some imaginative drawings they had designed. They certainly did not produce a “computer model” — nor did they claim they had. Nevertheless, Dawkins persisted in his claim that Nilsson had made a computer model that could deform a flat patch at random to produce a camera-like eye.

What’s wrong with this story?

Of course, we don’t know what really happened between Dawkins and Nilsson from 1991 to 1994. But let’s imagine ourselves traveling back in time and listening in on some imaginary phone calls.

Let’s Listen In

December 1991: Richard Dawkins (in England) rings up Dan-Eric Nilsson (in Sweden). 

Dawkins: “Hi Dan; Richard here. Say, remember that computer simulation of eye evolution that you told me about? Well, I just gave a Christmas lecture on it here, and I was hoping you could send me whatever you’ve published on it.”

Nilsson: “Oh, Richard, that was just an idea, a thought experiment. I never actually did the simulation, so of course I haven’t published anything on it.”

Dawkins: “Oh dear. But now I’ve gone and told a great many people that you did. I even showed them drawings of the various stages that I said were produced by your computer simulation! What should we do?”

Nilsson: “Well, I suppose I could try to create a computer simulation and let you know what happens.”

Dawkins: “Thanks, Dan. I would be most appreciative. I’ll send you a link to my Christmas lecture right away.”

Nilsson: “Good. I’ll be in touch.”

[Nilsson rings off.]

A year and a half later: Dan-Eric Nilsson (in Sweden) rings up Richard Dawkins (in England).

Nilsson: “Hello, Richard. Sorry it has taken me so long to get back to you, but we’ve been very busy here.”

Dawkins: “Good of you to call, Dan. Do you have some news for me?”

Nilsson: “I’m afraid it’s not good, Richard. My colleague Suzanne Pelger and I used computer graphics to model a flat retina atop a flat pigment layer, surmounted by a flat transparent layer. Then we wrote a computer program to try to simulate its evolution into a camera-style eye. As you specified in your Christmas lecture, we allowed the model to deform itself randomly 1 percent at a time, preserving only those changes that improved upon what went before. Thanks to a grant from the Swedish Natural Science Research Council, we were able to let the program run for an entire year. But even after a year, we were not much closer to generating a camera-style eye than when we first started. Since the model was programmed to deform itself at random, and almost all of those deformations made things worse, it took a year to improve even slightly upon the original flat patch.”

Dawkins: “My goodness. What can we do?”

Nilsson: “Well, I think we may have a way around this. Suzanne and I used computer graphics to modify the drawings from your 1991 Christmas lecture to make it easier for us to measure the appropriate parameters. Then we calculated how many 1 percent changes it would take to transform each drawing into the next in the series. By plugging our results into some standard equations from population genetics we calculated that the whole process could occur in as little as 364,000 years.”

Dawkins: “Splendid! 364,000 years is a mere blink of an eye, geologically speaking. How soon do you think you can publish your results?”

Nilsson: “We hope to submit a paper by November or December. Of course, there’s one problem: We cannot call this a computer simulation. It’s true that we used computer graphics to draw the figures and measure the appropriate parameters, and we used a computer to calculate our results. But as I said, our attempt at a real computer simulation was a failure. I think the paper I just described is the most we can hope to get past the reviewers.”

Dawkins: “Well, of course, you must do what you think is right. In any case, I eagerly await your publication. Cheerio.” 

[Dawkins rings off.]

How Eyes Can Evolve Quickly

Maybe that’s how a paper with no computer simulation got written so as to appear to support Dawkins’s pre-existing claim that a computer simulation showed how eyes can evolve quickly.

In 1995, Dawkins repeated his claim in a book titled River Out of Eden. “Is there a smooth gradient of change, from flat skin to full camera eye, such that every intermediate is an improvement?” he asked. And he answered:

Nilsson and Pelger began with a flat retina atop a flat pigment layer and surmounted by a flat, protective transparent layer. The transparent layer was allowed to undergo localized random mutations of its refractive index. They then let their model deform itself at random, constrained only by the requirement that any change must be small and must be an improvement on what went before. The results were swift and decisive. A trajectory of steadily mounting acuity [sharpness of vision] led unhesitatingly from the flat beginning through a shallow indentation to a steadily deepening cup, as the shape of the model eye deformed itself on the computer screen.

In 2003, mathematician David Berlinski exposed just how meaningless Nilsson and Pelger’s calculations were. Berlinski also blasted Richard Dawkins for falsely claiming that they had produced a “computer model.” And he blasted Nilsson and Pelger for persistently failing to correct Dawkins’s false claim. Berlinski rightly described the whole affair as “a scientific scandal.”

Yet the scandal didn’t go away. In 2004, Mark Ridley’s textbook Evolution stated that Nilsson and Pelger made a computer simulation that “allowed the shape of the model eye to change at random.” According to Ridley the model eye “then evolved in the computer, with each new generation formed from the optically superior eyes in the previous generation; changes that made the optics worse were rejected, as selection would reject them in nature.” And according to a Scientific Reports paper published in 2013, “as mathematically predicted by Nilsson and Pelger, a patch of light-sensitive epithelial tissue could evolve by natural selection into a camera eye within only about 364,000 generations.”

So instead of lying down quietly in its grave, Dawkins’s dead myth continues to walk among us, like a zombie.

Photo credit: ivkohouska, via Pixabay.