I received a wonderful four-page typewritten letter from a gentleman in Oklahoma detailing, chapter by chapter, his reaction to my book. He describes himself as “a nearly ideal representative of people who have doubts about evolution but who could be convinced. I’m a scientist and a farmer. I am also an evangelical Christian. My scientific training is in physics and meteorology. . and I’ve been a close observer of nature all my life. . I have taught science and mathematics classes at two colleges and a high school in Lousiana and Oklahoma.”
I won’t bore you with the stuff he liked (e.g., his favorite chapter was the one on biogeography). What I want to discuss was what he didn’t like: in particular, the idea that natural selection can build complexity over observed stretches of time. Here is what he says about the chapter on natural selection (his underlines):
“Chapter 5 is where I have the most problems in accepting what you say. Let me ask a few questions. You have looked at living things in great detail, far more than have I. You have seen how amazingly complex living things are. That complexity exists at the tiniest levels (DNA, proteins, cells) to the levels of complete organisms. Surely you must think to yourself, “Is it really possible that all this complexity happened by purely materialistic and naturalistic processes?” Or, more specifically, do you ever think “Is natural selection enough to account for such complexity?” Of course, mutations occur and, of course, natural selection occurs everywhere in the biosphere andf all the time. But, is it enough? I just don’t see how it could be. It is a ruthless conservative process. But, is it a truly creative process? I found your description of the evolution of bird flight (p. 39) to be inadequate. You say “It’s not hard to envision. . .” Yes it is! How did a complex thing like a feather ever develop by mutations and natural selection?”
If you try to convey evolutionary biology to nonbiologists, this plaint will sound familiar. Sure we have evidence for evolution, and we see evidence in the fossil record for adaptation (for example, in tetrapods adapting to a terrestrial environment), but how can we be sure that adaptive changes are caused by natural selection? This inability to visualize how the slow, step-by-step accretion of adaptations could create the amazing diversity of life on Earth is why natural selection was not firmly established in the scientific community until the 1930s or so, even though evolution, gradualism, and common ancestry were part of scientific dogma in the 1870s. It is not so much that the process of natural selection is hard to understand, or that it could be responsible for “simple” adaptations like antibiotic resistance in bacteria. Rather, it is whether there has been enough time for such a process to create all the complex adaptations we see around us. (I’m not talking about the ID objection about the sufficiency of selection to build adaptations without going through a maladaptive phase — a common but misguided creationist argument made infamous by Michael Behe). And, of course, the gentleman also raises problems about whether natural selection can produce novelty.
Well, the complexity issue is easily dealt with. Both Ken Miller and Richard Dawkins have written extensively and convincingly about whether selection can produce novel traits. The answer of course is yes, as most biologists can see intuitively. And I think it’s easy to convince people of this with the compelling examples that Miller and Dawkins have used in Only a Theory and Climbing Mount Improbable, among other places. But I think the heart of the objection is not the ability of selection to build novel, complex traits, but the time available for it to have done so.
As evolutionists, how can we address this “time” concern? We usually do it in two ways. First, we say that we can see selection building adaptations over time. The evolution of whales from terrestrial artiodactyls, for example, took about 10 million years, and we can see it happen in the fossils. But this begs the question, since the questioners are asking whether this kind of change can be due to natural selection, which is said to be ineffective over such periods. And of course we can only invoke the idea that we know of no process other than selection that could create such adaptive change. That is satisfying to scientists, but perhaps not so convincing to people like the gentleman who wrote me.
Second — and most often — we evoke the huge stretches of time over which selection has had to work: millions and billions of years. Indeed, such spans of time are not easily grasped by even the minds of evolutionary biologists. We are accustomed (and perhaps evolved) to thinking of times on the order of decades or centuries. So, we say, given the long eons since life began evolving, there has been plenty of time for selection to do its job.
I think a good way to meet this criticism is through mathematical modelling. We simply make a model of the evolution of a complex trait (or better yet, several of them), basing it on reasonable estimates of selection pressures, mutation rates, etc. Then we see how long it will take the model or the computer to construct the adaptation. Then we extrapolate to how many such adaptations it would take to evolve a new “type” of creature, say a bird from a theropod dinosaur. If our theory is right, we should be able to do this, and find that selection can indeed create adapations in reasonable stretches of time.
As far as I know, there has been only one attempt to do this: Nilsson and Pelger’s 1994 paper on the evolution of a complex camera eye from a flat, pigmented, light-sensitive eyespot. ( Nilsson, D.-E., and S. Pelger. 1994. A pessimistic estimate of the time required for an eye to evolve. Proc. Roy. Soc. Lond. B 256:53-58.). This was a mathematical model that I describe in chapter 5 of WEIT, and which Richard Dawkins summarizes here. (See the animation of this process on Mark Ridley’s Evolution website here.) Nilsson and Pelger showed that, under conservative assumptions, the eyespot would become a complex camera eye in a little less than 400,000 years. Since the earliest animals with eyes go back to about 550 million years ago, this span is enough for eyes to have evolved more than 1500 times in succession!
Apparently this model was not sufficient to convince my interlocutor, or he didn’t realize its implications. What I would like to see, and what I think would be a great boon to furthering acceptance of evolution, is more models of the Nilsson and Pelger type. When we tell people that there’s been sufficient time for everything to have evolved by natural selection, we need more hard models to back us up. Granted, making such models isn’t going to tremendously advance the career of an evolutionary biologist, but I still think they’re important.
The stages of eye evolution in Nilsson and Pelger’s paper, with n equal to the number of generations that elapsed in their model.
Ah, the wonders of science – a proposal for (a) falsifiable test(s).
This may not advance the career of an evolutionary biologist, but how about the developing career of grad students or undergrads? This could be in biology or computer science. Maybe start a new field of computer science ‘biologics’.
Would it make sense to compare the DNA of real organisms whose eyes resemble the different stages of Nilsson and Pelger, to see if the required changes in DNA are credible?
There is an article about e coli evolving to metabolize citrate. The experiment went like this, about 12 strains cultured under similar conditions. Citrate was in the media as well as glucose. (E. coli cant metabolize citrate. I dont know if this is common knowledge, it wasnt to me at the time I read the paper.) Along the way, every 500 or so generations, they’d freeze a culture of the bacteria. After 33,000 generations, 1 of the 12 strains was able to metabolize citrate. This was a 20+ year old experiment. Interestingly, they also looked at historical contingency.
This research is done by Dr. Richard Lenski’s group
This may or may not be a good example.
I recall that Russ Lande, in a paper about 30 years ago, looked at the question of what selection intensities would be required to turn Hyracotherium (also known as Eohippus, the ‘dawn horse’) into Equus (modern horses), and found that the intensities required were quite low: i.e. observed selection intensities in nature were quite sufficient to account for the adaptive evolution of horses. This conclusion should apply quite nicely to the origin of whales, which, like the evolution of horses, involves the remodeling of an ungulate skeleton. Lande’s conclusion is similar to Nilsson & Pelger’s, in that the time available is vastly more than is necessary. Phil Gingerch (of whale evolution fame) showed many years ago that short-term rates of evolution greatly exceed rates averaged over long time periods, and both Lande and Nilsson & Pelger’s results can be seen in this light.
The question of the origin of novelty and complexity can also be dealt with from another perspective: there is, in fact, relatively little novelty and complexity in life. Most of evolution is, to use Francois Jacob’s term, ‘tinkering’: using what you already have in slightly different ways. The more you know about comparative anatomy or, now, comparative genomics, the more you realize there is not much new under the sun. In the evolution of vertebrates, from lobe-finned fishes to mammals, skeletal elements have changed in size and shape, skeletal elements have been eliminated, skeletal elements have been fused, skeletal elements present in multiple copies (e.g. vertebrae) have been decreased and increased in number, but hardly any actually new skeletal elements have been incorporated. I mention the vertebrate skeleton, not only because it is what I know, but because it is what we know a lot about. Most of evolution is not the origin of novel, complex structures. Most of evolution is the gradual adaptive modification of pre-existing structures (or, better, pre-existing developmental programs for those structures).
Quite a bit more is known on the topic of eye evolution than that model from 15 years ago (and the linear changes don’t correspond to hypotheses about actual evolution anyway).
Evolution: Education and Outreach, vol 1, issue 4 is full of (free access) articles.
The following statement is kind of telling for me:
“Is it really possible that all this complexity happened by purely materialistic and naturalistic processes?”
The number of trained physicists who have either not grasped or never come across the effect of non-linearities on complexity always surprises me. It’s kind of a side point but I do think that a lot of people don’t really understand the potential effects of large numbers of relatively simple objects interacting by relatively simple rules.
Not exactly the same thing I know, still I keep hearing this “complex structures cannot arise from simple rules” from people in my field (and outside).
A problem with the linked animation is that you see only a linear, direct progress. This reinforces several misconceptions that evolution is straightforward and progressive. You don’t see any of the population, and the diversity of variation that is tried and discarded over time.
I just read this article over at RichardDawkins.net and I came over here to see if I can get some clarification. I was very surprised to read about the lack of numerical simulation in evolutionary biology. Does the community of evolutionary biology judge work involving numerical simulation to be somehow unsuitable for a PhD defense, and/or a peer-reviewed paper, and/or tenure? In my question, I’m not asking about the selling of evolution to the public. Am I correct in reading this this article to say that numerical simulation is unacceptable in this profession? If so, then why?
The initial condition (n = 0) starts with a transparent layer, a light sensitive layer and a pigmented layer. I would assume that there is also a connection (nerves) made to a control center (brain) which allows the organism to take advantage of what ever is gained being sensitive to light.
It would seem that you are starting with a COMPLETE EYE (primitive as it is) and explaining how to get a more complex eye rather that demonstating how the eye got started in the first place.
How did the eye get started?
Neither a brain nor nerves are necessary to take advantage of a light spot.
One possible use;
an organisms predator lives near the surface of a body of water. Whenever light stimulates the light spot, a flagellum is activated to propel the organism away from the light.
The mechanism can be as simple as a single chemical messenger.
There are also organisms alive today that make use of primative light spots despite anything close to a “brain,” flat worms for instance.
You could try out this argument, assuming he has or knows some children:
“How do you know your children are growing? Have you ever actually watched them grow? They don’t look any bigger now than they did yesterday, or the day before. Why don’t you believe that smaller children are miraculously swapped for larger children by God? You believe your children are growing because the small changes in them from day to day are gradual and normal, and every day the newly grown child is almost exactly like the way they were yesterday — but not quite.
“If children can grow from cellular blobs to complex adults in seventeen years, what kind of things do you think natural processes could achieve in a million years, or a billion?”
“If your child went on growing naturally at the same rate for a billion years they would be about 100,000 km tall — one quarter of the way to the moon — and their brain would be as big as Planet Earth. That’s a dramatic achievement for a simple well-understood natural process; but all it takes is time, and we’ve had lots of it. We don’t have huge children, but we do have a complex biosystem.”
Obviously the concept of that length of time is very difficult to grasp. So maybe the analogy with ordinary human growth will help. There are lots of other natural processes you could use in the same way.
Your illustrations, seems to me, are of the sort that are very nice for helping non-biologists (like me) grasp the idea of little bitty changes leading to great big differences over enough time. Other of the comments here are too technical to be very helpful for enlightening non-biologists or just educated laypeople.
A male produces sperm.
A female produces an ovum.
When they unite the result is a zygote which grows ultimately into an adult as determined by their DNA.
We start from a fertilized egg.
How did the eye get started?
BOB@11:
You need to read up on evolution by natural selection. That will answer your question.
I’ve been reading but I haven’t found an answer.
I thought that one of the points of this post was to explain how easy it is for the eye to evolve.
Simple question – How did the eye get STARTED?
Do you know the answer?
BOB’s last request:
“Simple question – How did the eye get started?”
From above:
“Nilsson and Pelger’s 1994 paper on the evolution of a complex camera eye from a flat, pigmented, light-sensitive eyespot. ”
An organism developed a light-sensitive spot. Then it could possibly detect which way the light arrived (“up”). This could have been an advantage over others that had no similar spot. Then it got a depression and worked better. Then it got deeper, developed a membrane, then a lens…see diagrams above.
Also see http://en.wikipedia.org/wiki/Eye#Evolution
and http://en.wikipedia.org/wiki/Evolution_of_the_eye
“How did the eye get started?”
This question is too vague to answer as posed. Most define an “eye” as something that does more more than just detecting light; eyes are capable of forming an image. The resolution of images varies widely across animals, so not all eyes are equal in performance.
If the progression from light-sensitive spot to image-forming eye is uninteresting, what transition is interesting? How cells became light sensitive? Or something else?
If this is more appropriate then I will ask how did the light-sensitive spot get STARTED?
With reference to the diagram above the first example (n = 0) has a layer of light sensitive cells, as well as a transparent cover and a pigment layer. When these are connected to a “brain” the result is an eye.
What would come before (n = 0)
How did the “eye” get started?
“how did the light-sensitive spot get STARTED?”
I’m no expert but my guess would be; “mutation”. You know, as in evolution basics; “Replication, mutation and selection pressure”. One creature in a big population was born with a mutation that created the light-sensitive spot. This proved to be a benificial traight … etc.
Light sensitive cells.
A real simple sketch of the development of light sensitivity.
Many different molecules are capable of absorbing light, including proteins.
From there, a next step would be to proteins that respond to light. These are opsins, which belong to a larger category of proteins called G-coupled proteins (http://dx.doi.org/10.1016/j.cub.2005.09.025). Some early opsins are found in blue-green algae (http://dx.doi.org/10.1016/S0168-9525(99)01959-9), and it’s fairly easy to see the advantage of a photosynthetic organism having light sensitive proteins. (Note: I’m not saying that animals are descended from blue-green algae; just using this as an example of how a unicellular organism could benefit from having opsins.)
Once you’ve got a gene for an opsin in the genome, you have the potential to express that gene in any kind of tissue, including neurons. So now you have a regulatory change that preferentially expresses an opsin in neural tissue. Another that specifically expresses it in sensory neurons.
Now you’re about at the point where you’ve got opsins probably being used as cnidarians use them (http://dx.doi.org/10.1371/journal.pone.0001054). For instance, Hydra do respond to light (http://www.pnas.org/content/48/8/1376.citation) but they don’t have eyes, and even the distinction between sensory neurons and other kinds of neurons is pretty fuzzy.
And now we’re very close to the point where Jerry’s original article picks up, with the transition from light sensitive neurons to image forming camera eye.
So there is a short but serious attempt to answer the question. A little time spent using Google Scholar to look for things like “opsin evolution” will reveal all sorts of interesting data.
Yes I am familiar with light sensitive cells. I have many of them. They are called FRECKLES.
What does the journey from a simple normal cell to a light sensitive cell and then to a light sensitive cell which is connected to something (information processor/nervous system/brain) that can gain advantage from having a light sensitive cell look like?
How did the “eye” get started?
Thank you for your patience.
🙂
BOB, you have been pointed to several places to go learn for yourself. You just keep asking the same question again and again. You have been told that natural selection found something that was a little better than nothing. Over time, it developed into more of an eye than before by slight improvements due to natural selection. Maybe a nerve nearby the light sensitive cell picked up the signal. No one can define every small nuance of development from start to finish over thousands of improvements over tens of thousands of generations. Can you give us a description of your last 500 ancestors?
“Maybe a nerve nearby the light sensitive cell picked up the signal.”
Does that mean that my descendants could have eyes where I now have freckles?
Where specifically can I go to find some insights into this particular question?
Thanks.
p.s.
I’m pretty sure that all of my ancestors for the last 500 generations had two eyes in the front of their head.
🙂
I enjoyed the following book and learned a lot:
A Natural History of Seeing: The Art and Science of Vision By Simon Ings
Released: October 13, 2008; 336 Pages; Published by W. W. Norton
From Amazon.com:
“A Natural History of Seeing delves into both the evolution of sight and the evolution of our understanding of sight. It gives us the natural science—the physics of light and the biology of animals and humans alike—while also…”
Thanks
🙂
wow…really helpful post, thanks for sharing.
I am surprised that people are still referring to Nilsson and Pelger’s paper seriously. It demonstrates nothing of the kind. For those interested, the paper is here.
The paper completely ignores the biochemistry of the eye, or its relationship with any other system in the body (nerves, brain, etc.).
The 1% change rate they use has no basis in biochemistry, and is entirely morphological in its measurement.
In the real world, the different types of eyes have very different biochemistries, and work together in different contexts with the rest of the organism.
In various types of eyes, the differentiation of cells is different, the way the information is transmitted is different, and much of the biochemistry is different. None of these facts were accounted for in any way whatsoever by the paper.
So sure, by ignoring biological reality, gradual evolution seems very simple.