Here’s the fourth video in the “Twelve days of evolution” series produced by PBS and “It’s okay to be smart”. It’s about the evolution of the eye:
This is a pretty good explication of how to refute the creationist claim that eyes couldn’t have evolved by natural selection, and were therefore created de novo. That claim itself rests on the notion that a complex “camera eye” like ours, with each part supposedly requiring all the simultaneous presence of all the other parts to function, can’t possibly have come from a stepwise adaptive process. Creationists argue, in fact, that Darwin realized this himself, and they quote this bit from On the Origin of Species, chapter VI:
To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.
But they invariably leave out the following bit, in which Darwin showed his genius by imagining existing eyes of different species, all functioning adaptively, put in an order that could correspond to a stepwise/adaptive evolutionary sequence:
. . . Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory.
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.
A vivid demonstration of how a camera eye could evolve in a stepwise fashion, starting with a simple light-sensitive spot, was given by a young Richard Dawkins in the Royal Institution’s 1991 Christmas Lectures, “Growing up in the Universe.” Here’s his demonstration, broadcast by the BBC:
This was later discussed in extenso (with nice drawings) in Climbing Mount Improbable (1996). You may, as I do, have a few quibbles about Richard’s using Sewall Wright’s adaptive landscape to imagine why the nautilus couldn’t evolve a lens in its eye.
If you’re interested in the paper referenced in the first video, it’s by Nilsson and Pelger, and was published in Proc. Roy. Soc. in 1994 (click the title below to get a free pdf). It’s based on a computer simulation, but the results are described accurately in the video. This is, in fact, one of the few papers in which scientists have tried to address the question, “How long does it take a very complex trait to evolve?” And as the video above notes, the answer is “Not as long as you think.”
Very enjoyable. And Richard Dawkins seems so young!
Pretty good for his 50 years, indeed.
Not in a blink of an eye, but 1829 of them!
Makes me think that while I wouldn’t want to hold my breath while lungs evolve, they too were easier to evolve than we may suspect … oh yes, they were: https://en.wikipedia.org/wiki/Lung#Evolutionary_origins .
Creationists are so quaint, I wonder how they evolved their belief? ‘Look Ug, don’t imagine an invisible imaginary friend that is responsible for you, that’s too big of a step. Start with an imaginary pet that want to visit your cave.’
Why not? At the time that your ancestors (and mine too) were evolving lungs, they had perfectly functional gills. Occasionally they had problems with being in pools drying up, but even then they had appreciable gas exchange capability from lining of the mouth, pharynx and oesophagus.
Well, when creationists claim this about eyes, they are simply displaying ignorance.
Nature already includes living examples of the stages of eye development, from light-sensing spots through highly precise camera eyes like ours.
And there are (at least) two examples of highly precise camera eyes: Mammals and Cephalopods. And the cool thing is: They are different and obviously evolved separately.
Dear creationist: Why did “the designer” design two similar eyes; one with the nerves wired “correctly” (nerves exiting the light-sensitive cells at the back — cephalopods) and one wired backwards (mammals) giving mammals a blind spot in the center of the field of vision?
Since “he” supposedly made the fish first, you’d think “he” would have just re-used the cephalopod “design”.
And what about blind cave tetras (and other blind cave dwellers) who have lost their eyes? Seems a rotten design. If they are “designed” to live in total darkness, why equip them with eyes in the first place?
I also like Dan Dennett’s rebuttal of the watchmaker argument:
The found watch was not made in one leap by a designer either!
It is the end result of a long chain of trial and error (human-directed evolution in design and technology) that goes back through cruder watches, clocks, the invention of wheels, cogs, axles, springs, etc. The invention of metallurgy, the use of fire. The development of agriculture — allowing people to have a stationary life in which to develop the technologies. Etc. (And it all required humans in the first place.)
So, the logical conclusion to draw is not of a single master watch designer; but rather of a long line of designers, working over millennia to result in that watch.
Just like in the evolution of living things (except no designers were involved).
I didn’t know about Dennet’s rebuttal. I like it! It is now added to the part of my brain that stores rebuttals to creationism.
A beachcomber finds a watch on the beach. There must be an explanation, she thinks – this could not have just appeared out of thin air. Nor could it have always existed.
A half a mile later, she finds the answer: a large, complicated machine that is churning out watches one by one.
She turns away, satisfied that she has hit bedrock, with no further inquiry needed.
Yes. I was going to point out the Canon EOS Mark III DSLR camera, an artifice eye, did not spring forth de novo but “evolved” from pin hole cameras dating back to 400 BCE.
Good paper (A Pessimistic Estimate of the Time Required for an Eye to Evolve).
A few hundred thousand years. Also worth highlighting: a 1% change over only 70 generations can lead to a length change of a factor of 2 (1.01^70 ~ 2). Of course, physicists generally do not like it when people use simple math to explain growth without understanding other boundary conditions, but if natural systems do not disobey the laws of physics they will keep growing, assuming it is to the specie’s advantage given the environment.
Religious people always talk about the complexity of eyes, but perception of sound is just as sensitive and complex. The hardness of hearing must be a metaphor for religious people.
“The hardness of hearing must be a metaphor for religious people.”
That’s pretty clever!
I still remember the first time I saw the evolution of the eye explained. It was in a Dawkins documentary I think, but it was a European scientist who did the explaining. It was so clear and so obvious and I had this idea that if everyone could see it, there’d be no more claims it couldn’t happen.
I was a pretty new atheist at the time, so still a bit naïve about evidence convincing people.
The PBS segment was bright and charming. I think a very effective quick explanation aimed at the current generation of our young.
The Dawkins explanation was filled with much more detail and was also well put together, but for a different generation.
I wonder how today’s kids would take the longer form Dawkins used.
I for one was ok with Richards’ use of the fitness landscape as a way of explaining why the nautilus does not have corrective lenses. I just take it that it is a bit more complicated than he had time to let on in this talk. The fitness peak that the nautilus occupies is has optimized for a slower lifestyle & less complex body including a less complex nervous system. It takes a pretty good visual center and other expansions in the brain to process and interpret all those images that a lensed eye provides, and those kinds of brains are expensive. For each benefit accrued by a more complex part, like a lensed eye, there are various accessory costs for that part. In my view this is why lensed eyes evolved from simpler eyes, and yet there are species with simpler eyes. Creatures with simple eyes can optimize (ascend a fitness peak) for cheaper and simpler nervous systems.
As an aside – it’s a silly little thing, but I always felt that Wright’s fitness landscape metaphor would be better if portrayals of the landscape had tiny discrete steps, like staircases running up and down everywhere, rather than smooth slopes. Because rolling up hills seems a little odd. Evolutionary change is generally in discrete steps, waiting for the incremental change from each small step of innovation. So I think walking up a staircase feels more intuitive than rolling up a hill.
While I’m new to Dawkins, I like to look for characteristic features of people’s writing and speaking. Here’s one of Dawkins’ from the video:
“I like to think of all those 100-million-old dramas that must have been witnessed through the pinhole camera eyes of ammonites.”
I’ve begun to spy and admire Dawkins’ knack for making me easily picture images I’d never bring to mind otherwise. In a flash, I saw a pin-holed chorus in the ancient oceans, one teeming with darting, shadowy activity.
You’ll see similar fine examples in any of his books. Has he earned a Pulitzer yet? Why not?
Yes, Steve Pinker quotes a beautiful example in The Sense of Style. I liked it so much I put it on my webCV.
This one is very well known, but perhaps it is new to you: We are all going to die, and that makes us the lucky ones.
That’s one of the few I know, but I hadn’t seen the video. The last words gave me goosebumps: “More, we are granted the opportunity to understand why our eyes are open and why they see what they do in the short time before they close forever.” Thanks.
Nice video, but it’s dispiriting that they feel the need to call the series “It’s Okay to be Smart”.
“The video’s claim that eyes have evolved independently 50-100 times is dubious.”
Wikipedia’s article on evolution of the eye also spits out that claim. Their source for it is this book:
http://www.amazon.com/Animal-Eyes-Oxford-Biology/dp/0199581142/ref=sr_1_4?ie=UTF8&qid=1450812719&sr=8-4&keywords=animal+eyes
I quickly flittered through the preview, online version, but some pages aren’t available. I didn’t see the 50-100 times claim in the first couple chapters. Doesn’t mean it’s not there. I kept hunting, and though I didn’t find the source to the 50-100 times claim anywhere, I found something that interested me:
This is from the abstract of an article from 2003, “Evolution of eyes and photoreceptor cell types”:
“While morphological comparisons of eye anatomy and photoreceptor cell types led to the view that animal eyes evolved multiple times independently, the molecular conservation of the pax6 eye-specifying cascade has indicated the contrary – that animal eyes evolved from a common, simple precursor, the proto-eye.”
Link to article:
https://www.dropbox.com/s/vifj4wbujkfubtp/Evolution%20of%20eyes%20and%20photoreceptor%20cell%20types.pdf?dl=0&preview=Evolution+of+eyes+and+photoreceptor+cell+types.pdf
I imagine it’s possible that a very early version of a photosensitive patch might have happened once, while you could still say many later developments represent ‘independent’ evolutions of the eye.
Seems reasonable. A common starting point, which had nothing to do with capturing an image. Dozens (maybe) of evolutionary pathways and a “repurposing”, giving many different morphologies capable of capturing an image. There’s a lot to think about, buried in this.
Thanks for that. Interesting paper.
Nilsson has done some follow-up studies on eye evolution: “Eye evolution: a question of genetic promiscuity.” Current Opinion in Neurobiology 14 (Aug 2004): 407-414.
And “The evolution of eyes and visually guided behaviour.” Philosophical Transactions of the Royal Society of London B (Biological Sciences) 364 (12 Oct 2009): 2833-2847.
btw Nilssen bumped into the creation/evolution wars on this very issue when David (King of the Tortucans) Berlinski lit into his work, occasioning his retort http://www.talkreason.org/articles/blurred.cfm#lund
I responded to Berlinski as well (in the early stages of #TIP project) on the eye issue and another of Berlinski’s blunderings, the reptile-mammal transition fossil record (a fascinating scholarly daisy chain where Berlinski riffed off Phillip Johnson channeling full blown oddball creationist John Woodmorappe), in
http://www.talkreason.org/articles/Berlinski1.cfm)
Nilsson and Pelger did NOT use a computer simulation. Richard Dawkins erroneously stated that they’d done so in one or two of his books, and, like many other people, I repeated this error in internet discussions for a while.
I’m not certain now, but I seem to remember it was an article by David Berlinski that first drew this error to my attention. Of course, I then read the paper for myself, and didn’t just take his word for it. It’s pretty clear from the paper that they didn’t use a computer simulation, and I believe I also saw something in which Nilsson or Pelger stated this explicitly. I’m a little annoyed with Dawkins for putting me in the position of being corrected by Berliniski!
“Berlinski is right on one point only: my paper with Pelger has been incorrectly quoted as containing a computer simulation of eye evolution. I have not considered this to be very serious, because a simulation would be a mere automation of the logic in our paper. A complete simulation is thus of moderate scientific interest, although it would be useful from an educational point of view.”
From: Beware of Pseudo-science:
a response to David Berlinski’s attack on my calculation of how long it takes for an eye to evolve, by Dan E. Nilsson. There is a copy of this available on Talk Reason, James Downard gives a link just above.
I agree with Dr Nilsson. Once the logic is worked out, and the results already calculated, instigating such a simulation is just a technical exercise. It adds nothing to our understanding. On the other hand, I understand your annoyance. Dr. Dawkins should have been more careful. Creationists claim victory over these sorts of trivial mistakes, while they completely mangle most of the underlying science.
Berlinski certainly harped on that misstatement of Dawkins (who is a human being, after all, not an oracle), though Berlinski bypassed the actual content of Nelsen/Pelgar, who had built physical models (reflecting eye forms known to exist in nature) that could today be done in computer simulations (which analogy is probably how Dawkins got off on his misphrasing) and carefully analyzed the optics of those. That was the Berlinski piece that occasioned the Talk Reason exchanges I noted in an earlier comment on this thread (including Berlinski’s glib channeling of creationist Woodmorappe on the reptile-mammal transition, paper linked at my http://www.tortucan.wordpress.com as well).
The important thing to remember about eye evolution is that the stages involved are all known in nature, and that none of the full blown eye we have has to be invented de nova, but clearly builds on a long windup of genetic subsystems (the details of which antievolutionists neither helped to generate nor pay much attention to that body of work regulr scientists keep doing).
A relevant article maybe:
Why do animal eyes have pupils of different shapes?
http://advances.sciencemag.org/content/1/7/e1500391
Very interesting. I like Figure 1.
“(C) Results of statistical tests on the relationship between foraging, activity, and pupil shape. Multinomial logistic regression tests were conducted with foraging mode, activity time, and pupil shape as factors and genus as a covariate. Relative-risk ratios were computed for having a circular, subcircular, or vertical-slit pupil relative to having a horizontal pupil as a function of foraging mode or diel activity. Activity time proceeded from diurnal to polyphasic to nocturnal. Foraging mode proceeded from herbivorous prey to active predator to ambush predator. When the relative-risk ratio is greater than 1, the directional change in the independent variable (foraging or activity) was associated with a greater probability of having the specified pupil shape than a horizontal pupil.”
It’s just cool that they used multinomial logistic regression to examine the relationship between pupil shape and their independent variables. I heart seeing biologists using Epi methods.