Thursday, February 09, 2006

Darwin Day Talk

So the big talk went well yesterday. Around thirty people showed up. If there were any creationists in the audience, they didn't say anything. Here's the Cliff's Notes version of what I said.

I began by showing a few of those cartoons Ken Ham likes so much, in this case drawn from his book Creation Evangelism for the New Millenium. You now the ones I mean. The ones that show evolution as the foundation of a secular worldview that promotes abortion, homosexuality, family breakup and all that other nasty stuff. I then rhetorically asked what kind of scientific theory could possibly provoke a response that irrational.

From here I discussed a few common myths about evolution. Evolution is neither a theory about the origin of the universe, nor about the origin of the Earth, nor about the origin of life. I gave examples from various cable news pundits illustrating each of these fallacies. Likewise, evolution is neither an atheistic theory nor is it a theory of random chance. I pointed out that the claim that humans and lobsters shared a common ancestor does not imply that we should expect to dig up a half-human half-lobster fossil. Finally, I explained why evolution does not say we evolved from apes.

After clearing up what evolution is not, I spent a few moments explaining what evolution is. I identified the hypotheses of common descent and natural selection as the primary shaper of that descent as the core of the theory.

Then I launched into the longest part of the talk, wherein I laid out some of the evidence for common descent and natural selection. The audience consisted primarily of students and I did not want to assume they were familiar with this area. Judging from the comments I got after the talk, this seems to have been the right decision.

I began with the fossil record, and argued that fossils provide three types of evidence for common descent. First, the broad history of life as revealed by the fossil record is perfectly consistent with common descent. No Cambrian rabbits, to use a famous example. Second, creationist protestations notwithstanding, there are droves of transitional forms in the fossil record. Finally, the geographic distribution of fossils supports common descent. For example, armidillos are native to South America, and that is also where you go to find the fossil ancestors of modern armidillos.

Next up was the issue of anatomical homologies. I used the ye olde forelimb example. There's a reason it's a classic. Why do the forelimbs of humans, whales and bats, among others, use the same bones in the same relative positions? This makes no sense from an engineering standpoint, but makes perfect sense if all of these critters evolved from a common ancestor.

Then came embryology. Why do the early developmental stages of very different organisms nonetheless look nearly identical? Why do human embryos form tails and yolk sacs? Why is it that birds possess the genetic information for making teeth when that information is not expressed in modern birds?

Then we talked about vesitigal structures like pelvic bones in whales in snakes. I brought up many others as well. Everyplace else we find pelvic bones they are there for attaching legs to torsoes. If whales and snakes evolved from critters with legs, this is easy to explain. If not, then what are they doing there?

I said a few words about biogeography as well, but I won't belabor that here.

Finally I discussed some of the genetic and molecular evidence for common descent and thisis where things got interesting. I used the example of cytochrome-c. I explained that all organisms possess some form of this protein, but that there is enormous functional redundancy in its structure. In other words, there are many different functional forms of the protein. Human and yeast cytochrome-c differ in over forty precent of the protein, but human cytochrome-c works perfectly well when transplanted into yeast.

How then to explain the fact that human and chimp cytochrome-c is identical? More genearlly, how do we explain the fact that the phylogenetic trees constructed by analyzing cytochrome-c across the animal kingdom perfectly matches the phylogenetic trees constructed by other methods. I argued that this fact alone argues strongly for common descent.

These patterns certainly can't be epxlained funcitonally, after all. And given the sheer variety of functionla cyctochrome-c proteins, we can't explain it as the result of chance either.

At this point an audience member asked how the ID folks explain this fact. I had to confess I didn't know. The only ID proponent I could think of who has addressed this subject was Cornelius Hunter, who did so in his contribution to Dembski's anthology Uncommon Dissent. But his only reply was to hold out the vague hope that there was some functional explanation after all for the patterns. Does anyone know of any other ID reply to this point?

I completed my round-up of the evidence for common descent with a discussion of retroviral scars. For example, the genomes of primates reveal numerous insertions of retroviral DNA. As with the cytochrome-c, the patterns of these insertions matches perfectly with the phylogenetic trees constructed by other means.

Next up was natural selection. I began with Darwin's description of natural selection from The Origin. Then I used Dawkins' “Methinks is like a weasel,” experiment to illustrate how it is possible in principle for natural selection to craft complex structures.

I then provided brief discussions of evolutionary computation, known instances of speciation via artificial selection, field studies of natural selection, laboratory experiments on selection that have shown that new functionalities can evolve, ring species, and artifical life. After this summary I argued that the upshot is that any claim that the adaptations of modern organisms are not the result of natural selection will have to be defended by appeal to specific biological data. There is no sound, armchair argument that can show that natural selection is fundamentally incapable of doing what biologists attribute to it.

I next offered three lines of evidence to show that natural selection really was responsible for crafting the complex systems in nature. I pointed to the fact that many complex systems appear to be cobbled together from parts that were readily available in related organisms. I used the examples of the bee-attracting gizmos of orchids. I also observed that, again, ID protestations notwithstanding, scientists had discovered plausible series of intermediates for a great many complex structures.

Related to this line of evidence are the many “senseless signs of history,” to borrow Gould's phrase, that we find in modern ogranisms. I pointed to the fact that we breathe and swallow through the same tube as an example. This makes perfect sense in the light of evolution (which posits that this system evolved from more primitive systems in ancient lungfish). I pointed to other examples as well, such as the weakness of our lower backs and the backward wiring of our eyes.

The final line of evidence came from the applications of game theory to problems of animal behavior. Mathematical models based on game theory explicitly assume that natural selection is the cause of the behaviors being analyzed. The success of these models is testimony to the correctness of this assumption.

This was the longest section of the talk. I next gave a short biography of Darwin and described what, exactly, his contribution to biology was.

Then came a round-up of various anti-evolution arguments. I treated Behe's claims about irreducible complexity in detail, and also said a few words about the tautology argument and the thermodynamics argument. I chose those three because all of them have been prominent lately, and all of them represent attempts to show that evolution is false while making very little appeal to the actual biological data. I used the following representative statement from the Judge's decision in the big Dover case:

The immune system is the third system to which Professor Behe has applied the definition of irreducible complexity. In Darwin’s Black Box, Professor Behe wrote that not only were there no natural explanations for the immune system at the time, but that natural explanations were impossible regarding its origin. However, Dr. Miller presented peer-reviewed studies refuting Professor Behe’s claim that the immune system was irreducibly complex. Between 1996 and 2002, various studies confirmed each element of the evolutionary hypothesis explaining the origin of the
immune system. In fact, on cross-examination, Professor Behe was questioned concerning his 1996 claim that science would never find an evolutionary explanation for the immune system. He was presented with fifty-eight peer-reviewed publications, nine books, and several immunology textbook chapters about the evolution of the immune system; however, he simply insisted that this was still not sufficient evidence of evolution, and that it was not “good enough.”

Since I was mostly out of time at this point I had to jettison the part where I disucssed that recent Washington Post article about the odious Caroline Crocker. See this post for details on that.

So instead I wrapped it up with Darwin's old “There is grandeur in this view of life” quote, answered questions for another hour and a half, and called it a night. All in all, a successful evening.


At 9:01 AM, Anonymous JY said...

Finally, I explained why evolution does not say we evolved from apes.

By that did you mean we didn't evolve from a modern species of ape? Because the common ancestor of Homo sapiens and Pan troglodytes would surely be classified as an ape.

Also, the common ancestor of, say, humans, baboons (an old world monkey), and marmosets (a new world monkey), would surely be classified as a 'monkey', so we did indeed, for any reasonable definition of 'monkey', evolve from monkeys, although I often hear protestations to the contrary.

At 10:19 AM, Blogger Craig Pennington said...

"[S]o we did indeed, for any reasonable definition of 'monkey', evolve from monkeys, although I often hear protestations to the contrary."

Lay classifications like "monkey" and "ape" are not specific and lead to misunderstanding. Saying "we descended from monkeys" without clarification and given the inexact lay understanding of the the term "monkey" is more misleading than Jason's shorthand.

The reason to prefer the shorthand is because a biological "reasonable definition" is extremely misleading to a lay audience who have their own definition of the terms -- and it usually equates with modern non-human species. It is more important to explicitly deny this link (rather than argue over the classification of ancestral species,) because it counters a very common fundamental misperception. It is very important to emphasize that we did not evolve from modern apes or modern monkeys -- that these modern species are as distinct from our common ancestors as we are.

That said, by any reasonable definition of the term, you, Jason and I are apes.

At 12:02 PM, Blogger Salvador T. Cordova said...

Given your outline, I'm confident your presentation was well received. I'm glad that if there were any creationists in the audience, they were at least not disruptive.

I think you argue the case for your side almost better than anyone, and I'm sorry I wasn't there.

I maintain that any student seriously interested in defending ID should be thouroughly knowledgeable of the objection you raise.


At 1:32 PM, Anonymous JY said...


I agree that clarification is required, but a common refrain from some defenders of evolution is that 'evolution doesn't say we descended from apes' or 'evolution doesn't say we descended from monkeys', without clarification, or with the vague clarification that monkeys (or apes) and humans descended from a common ancestor. This, I think, is weasly -- any evolution denier who looked at a proposed common ancestor for chimps and humans would identify it as an ape, and any evolution denier who looked a a proposed common ancestor for marmosets and humans would identify it as a monkey. So I think we should never say 'evolution doesn't say we evolved from apes', we should always say 'evolution doesn't say we evolved from modern apes', or admit that we did in fact evolve from apes.

The idea that we evolved from a modern species is perhaps a common misconception, but I think the anti-evolutionists' chief objection is to the idea that we evolved from some monkey-like or ape-like ancestor, regardless of whether that ancestor is around today, so we shouldn't mince words -- that's what evolution says.

At 3:20 PM, Blogger Craig Pennington said...


I urderstand your point. I disagree that it is weasly -- but to be safe, it is better to be specific.

The misunderstanding that I think is more important than whether classifications of modern species should be applied to historical species is not unique to creationists. It is probably shared by many who superficially consider "evolution" to be true. That is, the imposition of the The Great Chain of Being on the leaf nodes of the tree of life. That is a key and fundamental misunderstanding -- a failure to properly credit the historical aspect of evolution. For a randomly chosen non-Homo sapiens vertibrate species X, we have a most recent common ancestor between Homo sapiens and X, N. I'd wager that Homo sapiens share more morphological traits with N than we do with X.

That is, in my opinion, an important distinction that is missed when we say we evolved from some modern category in which we place X (and would likely include N if N were to be magically transported to today.)

It is exactly the failure to make that distinction that leads to the "we never see a cat giving birth to a dog" idiocy we get from so many anti-evolutionists. That's not what evolution says. A bit of ephemera came to my attention recently which really drove this point home to me. It is some old videos of the now extinct thylacines -- Tasmanian wolves. Looking at these animals, their physical features and the way they moved in those videos, I could see the relatedness to other antipodean marsupials. I was thinking that this might be what it looked like if a kangaroo gave birth to a dog -- but that's not quite right. It is the common ancestry that I see, and it's easier for me to see it because they are so different than mammals in the rest of the world.

The common ancestor of the thylacine and the kangaroo species was neither. It would be incorrect to say either evolved from the other. And that's exactly the distinction made by saying "evolution doesn't claim we evolved from apes" when "apes" are understood by the audience to mean "non-human modern apes."

At 10:42 AM, Blogger PZ Myers said...

My talk was better attended...but I didn't get anywhere near the number of questions you got.

I was sending out a similar message too. I managed to get in the Crocker nonsense by starting my talk with it.

At 2:55 AM, Blogger Jeff said...


This talk sounds fascinating, I wish I could have seen it. I discovered your blog recently while doing research to back up the scientific side of a creationism/evolution argument and I'm glad I did!

I have one question that I've been trying to track down an answer to.

Over the course of this debate, my opponent has gradually retreated from his assertion of a "theory of faith" and his claim that "faith" and "evolution" are both potential theories for the origin of life. He's basically got one point left that he won't budge from:

He asserts that "mutation in DNA" is so unlikely as to be possible only by intervention from a Higher Power.

As part of this he claims that scientists say that DNA mutation is "random" or "by chance" and that science has been completely unable to explain why DNA mutates.

I've rebutted these points to my own satisfaction on logical grounds alone, but I'm curious:

Why *does* DNA mutate?

What causes it? I'd love to have some more solid answers, just for my own satisfaction.

Thanks in advance,

At 8:19 AM, Blogger MissPrism said...


Ask your friend what he means exactly!

Mutation - in the sense of change to the DNA sequence - can happen in many ways: by damage from UV light or free radicals, by the enzyme that replicates DNA making mistakes (its mistake rate is about one in fifty billion, meaning you have about 100 mutations your parents didn't), or by the recombination machinery going wrong and deleting or duplicating bits of DNA.

What your friend probably means is beneficial mutations, that is, ones that make a 'better' organism. A lot of mutations probably have no effect at all, and some will be harmful: the proportion that will be beneficial is still being debated, but it doesn't need to be very high as natural selection will preserve only the beneficial mutations.

Incidentally, one can change the mutation rate of bacteria by genetic engineering, and under some circumstances the 'mutator' strains will outcompete the normal ones, proving that mutation ain't all bad.

At 12:18 AM, Anonymous Robbie34 said...

"Next up was the issue of anatomical homologies. I used the ye olde forelimb example. There's a reason it's a classic. Why do the forelimbs of humans, whales and bats, among others, use the same bones in the same relative positions? This makes no sense from an engineering standpoint, but makes perfect sense if all of these critters evolved from a common ancestor."

I have heard this example many times, however I believe it to be the downfall of the common ancestor argument.

Let me ask the question a little differently. How does one explain such wide variations in kind (species) while maintaining such alignment in type (anatomic homologies)? With completely random processes taking place throughout evolutionary time, why has such harmony been preserved in each organism (one head, one brain, one heart, two lungs, two eyes, two ears, one mouth, one liver, kidneys, stomach, intestines, reproductive organs, relative positioning of each of these items within the body, etc.)? I would expect with such wide variation in kind (millions of species), we should have exponentially wider variation in type. Where are the evolutionary-mature beings with 6 eyes, 3 hearts, 8 lungs, 4 legs, and 2 brains?

I would like to leave you with one additional thought. As you offer your evidence for evolutionary theory, please consider that all of your examples support a Creator working methodically on His creation. Embryology, vesitigal structures, biogeography, genetic and molecular similarities are just as logical for a creation argument... just because He wanted them that way!

I look forward to your responses.

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