Thursday, July 17, 2008

PZ Myers' GECCO Talk

Update: Myers has posted his notes and slides.

PZ Myers gave his keynote address at GECCO on Tuesday morning, July 18th. Fortunately (or maybe unfortunately), he didn't breathe any fire, sacrifice any children by plucking out their heart, or butt-rape any consecrated crackers on stage.

Instead he gave a pretty darned interesting talk entitled "Developmental Perspectives for Understanding Evolution," which was basically an overview of evo-devo, with mention of some interesting recent experiments. The main argument of the talk, and evo-devo in general, is that you have to understand development to understand evolution.

One of the early slides had these two quotations:

"Everything is the way it is because it got that way." --D'Arcy Wentworth Thompson, 1917

"Evolution is the control of development by ecology." --Van Valen, 1973

Myers then went on to talk about how development is a hierarchical process that is essentially a series of binary decisions. Cells divide and differentiate, and when they do so they make choices that determine, and thus restrict, their fate. This whole bit reminded me of the most interesting part of the panel talk at last year's GECCO with Lewis Wolpert, Richard Dawkins, and Steve Jones. I didn't attend, but I have a link to the video here. The bit I found most interesting was when they were arguing whether or not it was possible to evolve a mouse with wings (which also has a wierd synergy with parts of Myers' talk, as we'll see later).

Anyway, then he talked a bit about epigenetics and the role of the environment in development, and talked about how the patterns that form during development are not directly encoded by the genes, but are an emergent effect of the process of development. He stressed that this doesn't mean that genes aren't important, just that the environment is important as well.

Then he talked about the opposite concepts of plasticity, which he defined (short version) as the ability of an organism to react to an internal or external change, and canalization, which are constraints which restrict the amount of change. As for the concept of evolvability, the capability of an organism to change, he said he didn't really believe in it as a distinct concept.

A discussion of toolbox genes then followed, in which Myers talked about how biologists used to assume that the difference in the DNA between organisms like a fly and a whale would be enormous, qualitatively, but as it turns out, about 80% of the genes in such animals is carrying out very similar functions, like determining where on the head the eyes are going to be constructed. The PAX-6 gene is a toolbox gene for use in building eyes, and both flies and mice (and by implication many other organisms) use this same gene for doing the same thing. Citing Putnam, Myers said that only about 15% of the genes are unique to an organism, in terms of their function.

Then he talked about genetic assimilation and accomodation (which Myers actually talks about at length here). He also mentioned the Baldwin Effect.

At this point in the talk he started to give some concrete examples, which was a nice way to illustrate a lot of the theory he'd been discussing. He talked about how a species of sheep that lives in a colder environment may, over time, evolve a thicker coat of hair. Or, perhaps if the climate is variable, the sheep evolves such that in warmer conditions it grows at thinner coat, and in colder conditions, it grows a thicker coat. The difference is between a kind of hard-wired trait, and one that is plastic, and can adapt to the changing environment.

Another example was from a 2006 paper by Suzuki and Nijhout, Evolution of a Polyphenism by Genetic Accommodation. Basically, the experimenters were able to artificially select for higher plasticity in the larva of the tobacco hornworm, Manduca sexta. They were able to manipulate the evolving population such that after only a short number of generations, individuals were able to change their color depending on temperature (go read Myers' post on it for all the details).

Then he brought up another cool example of the role of regulatory genes, from work by Chris Cretekos involving the differences in development between mouse and bat forelimbs. Myers' blogged about this work too. Go check it out. There are cool pics of bat embryos. Basically the researchers were able to remove regulatory genes that enhance the expression of the gene PRX1, which controls the growth of forelimbs. They spliced this regulatory sequence from the bat into the mouse, and measured the effects. Myers warned us that we weren't going to see images of mice with bat wings, and not to be disappointed. I was, a little. Instead, the mice grew longer forelimbs. Nothing like a bat's, but still longer. They also deleted this sequence in the mice and measured the result, and found that there was little to no effect, which suggests a fair amount of redundancy in the regulatory genes that mediate such kind of growth.

In conclusion, he reiterated that:
  • Multicellular organisms are coherent arrays of patterned elements
  • Organization is the product of interactions between genes, cells, and the environment
  • Both evolution and development are dynamic processes, unfolding over time, not static lists of parts
The Q&A followed. I didn't take very good notes for that part, but one thing I noted was that he admitted up front that he wasn't that familiar with the field of evolutionary computation, which is fine. Though I wish he had attended a couple of sessions, especially those related directly to the topic of his talk. There was a tutorial on Generative and Developmental Systems that I really would have liked to have heard his reaction to. But in general I would have liked to have heard his reaction to some of the approaches and encodings, even if he wasn't familiar with the intricate details...just a critique of the overall approach.

But it was a good talk...better than most keynotes I've seen at GECCO in the past. In studying and trying to model cognition, I've developed a more profound respect for the role of time, and of trying to understand the extent to which certain cognitive functions have evolved to be highly plastic and which are less adaptive during our development. Myers spoke directly to these kinds of issues, and gave a very informative overview of many important concepts in evolutionary biology today.

Then he pulled a live baby out of his briefcase and bit its head off.


Anonymous said...

"Then he pulled a live baby out of his briefcase and bit its head off. "


Shame on you, Mr Myers! Shame on you!

breakerslion said...

"Then he pulled a live baby out of his briefcase and bit its head off."

Only one? He's mellowing with age.

Travc said...

For PZ not being familiar with evolutionary computation, he seems to have done a pretty good job of hitting exactly the relevant points.

Philip said...

You got noticed by the man himself:

Derek James said...

Yeah, I've noticed a substantial spike in my blog traffic. :)

Thanks to all the visitors from Pharyngula.