I’m going to get off a quick summary of this afternoon’s talks, then I have to run down to the poster session to find out what the grad students have been doing. Are we having fun yet? I’m going to collapse in bed tonight, and then unfortunately I have to catch an early flight back home, so I’m going to miss a lot of cool stuff tomorrow.
My brain is most wonderfully agitated, which is the good thing about going to these meetings. Scientists are perverse information junkies who love to get jarred by new ideas and strong arguments, and meetings like this are intense and challenging. I’ve only got a little time here before the next session, so let me rip through a short summary of my morning.
So here I am at the IGERT Symposium on Evolution, Development, and Genomics, having a grand time, even if I did get called out in the very first talk. There were two keynote talks delivered this evening, both of which I was anticipating very much, and which represented the really good side of science: two differing points of view wrestling with each other for consensus and for testable, discriminating differences. They also had dueling t-shirts.
Fossils are cool, but some of us are interested in processes and structures that don’t fossilize well. For instance, if you want to know more about the evolution of mammalian reproduction, you’d best not pin your hopes on the discovery of a series of fossilized placentas, or fossilized mammary glands … and although a few fossilized invertebrate embryos have been discovered, their preservation relied on conditions not found inside the rotting gut cavity of dead pregnant mammals.
You’d think this would mean we’re right out of luck, but as it turns out, we have a place to turn to, a different kind of fossil. These are fossil genes, relics of our ancient past, and they are found by digging in the debris of our genomes. By comparing the sequences of genes of known function in different lineages, we can get a measure of divergence times … and in the case of some genes which have discrete functions, we can even plot the times of origin or loss of those particular functions in the organism’s history.
Here’s one example. We don’t have any fossilized placentas, but we know that there was an important transition in the mammalian lineage: we had to have shifted from producing eggs in which yolk was the primary source of embryonic nutrition to a state where the embryo acquired its nutrition from a direct interface with maternal circulation, the placenta. We modern mammals don’t need yolk at all … but could there be vestiges of yolk proteins still left buried in our genome? The answer, which you already know since I’m writing this, is yes.
You know how people can be going along, minding their own business, and then they see some cute big-eyed puppy and they go “Awwwww,” and their hearts melt, and then it’s all a big sloppy mushfest? I felt that way the other day, as I was meandering down some obscure byways of the developmental biology literature, and discovered the dicyemid mesozoa … an obscure phylum which I vaguely recall hearing about before, but had never seriously examined. After reading a few papers, I have to say that these creatures are much more lovable then mere puppy dogs. Look at this and say “Awwwww!”
O dicyemid mesozoan, how do I love thee? Let me count the ways.
Wilkins tagged me. It’s all his fault.
This is supposed to be a historical meme…why bother me with this? I think it’s because philosophers have a professional obligation to annoy people with weird questions, and Wilkins takes personal pleasure in poking me now and then, the brute. Here’s what I’m supposed to do.
- Link to the person who tagged you.
- List 7 random/weird things about your favorite historical figure.
- Tag seven more people at the end of your blog and link to theirs.
- Let the person know they have been tagged by leaving a note on their blog.
Favorite historical figure?? I don’t suppose I can name the progenote or urbilaterian, but because this was started by some historian somewhere, I have to restrict myself to some boring recent human being; and like Wilkins, I should avoid the obvious choices, although in his case Frederick II Hohenstaufen was a cool dude.
I guess I’ll name another cool dude…
The author of All-Too-Common Dissent has found a bizarre creationist on the web; this fellow, Randy Stimpson, isn’t at all unusual, but he does represent well some common characteristics of creationists in general: arrogance, ignorance, and projection. He writes software, so he thinks we have to interpret the genome as a big program; he knows nothing about biology; and he thinks his expertise in an unrelated field means he knows better than biologists. And he freely admits it!
I am not a geneticist or a molecular biologist. In fact, I only know slightly more about DNA than the average college educated person. However, as a software developer I have a vague idea of how many bytes of code is needed to make complex software programs. And to think that something as complicated as a human being is encoded in only 3 billion base pairs of DNA is astounding.
Wow. I know nothing about engine repair, but if I strolled down to the local garage and tried to tell the mechanics that a car was just like a zebrafish, and you need to throw a few brine shrimp in the gas tank now and then, I don’t think I would be well-received. Creationists, however, feel no compunction about expressing comparable inanities.
Since I wrote about the wacky creationist who couldn’t wrap his mind around the idea that plants and animals are related, and since I generally do a poor job of discussing that important kingdom of the plants (I admit it, I’m a metazoan bigot…but I do try to overcome my biases), I thought I’d briefly mention an older review by Elliot Meyerowitz that compares developmental processes in plants and animals. The main message is that developmental processes, the mechanisms that assemble the multicellular whole, are very different in the two groups and are non-homologous, but don’t get confused: the basic cellular processes are homologous, and there’s no doubt that we are related. The emphasis in this paper, though, is the evidence that plants and animals independently evolved multicellular developmental strategies. There is some convergence, but the tools in the toolbox are different.
We had Neil Shubin here last week, and now Jerry Coyne is guest-blogging at The Loom. I look forward to the day that I can just sit back and invite prominent scientists to do my work for me here.
Although, I have to say that while Coyne is largely correct, he’s being a bit unfair. He’s addressing Olivia Judson’s recent article on “hopeful monsters”, a concept Coyne and the majority of the biological community reject. I reject it, too, but I think there are some legitimate issues that are associated with the idea that are also all too often and unfortunately discarded.
One point that Coyne handles well: there is a disconnect between the magnitude of genotypic changes and phenotypic effects — a single point mutation can cause amazing morphological changes. As Coyne points out, though, although this can happen, it’s not likely to be a major force in evolutionary change. Dramatic, single-step phenotypic effects are the kinds of things that geneticists select for, but they are also exactly the kinds of things that nature selects against. Evolution is much more likely to sidle up towards a major change by successive smaller steps, since those small changes are less likely to be accompanied by major deleterious side effects. Also, phenotypic outcomes of development should be robust to be advantageous, which typically means that there are many regulatory events cooperating to produce them — and they are therefore buffered by multiple controls.
But please, let’s not always dismiss Richard Goldschmidt when discussing “hopeful monsters”. It really wasn’t that awful an idea. Goldschmidt worked on stable variations in organisms: he studied sex differences (ever noticed that males and females have pretty much the same genes, but different phenotypes?) and metamorphosis (similarly, an organism builds two or more very different morphologies with exactly the same genome). He postulated that there could be specific, well-structured, stable nodes of patterns of gene expression — genes weren’t generally fluid, but tended to lock in to particular states. If he were writing today, he’d probably be bringing up the notion of attractors in chaos theory; the ideas are very similar. In that context, he was proposing a worthy concept that should have been taken more seriously than it was — Mayr’s hatchet job was particularly awful.
The “hopeful monster” concept was not shot down by the synthesis — it was ignored. I think it’s been dismantled by developmental biology, though; what we’ve learned is that the stable morphological types we see in a single species are not simply fortunate stable nodes in a nucleus that can be tuned in different ways, but that each are the product of many generations of slow sculpting by the processes of evolution, and that they are riddled with clumsy kluges that aren’t the outcome of some elegant global pattern switching mechanism, but of a long history of small tweaks.
Now also, Coyne is no fan of evo-devo, and he briefly voices the suggestion that the evolutionary developmental biologists are among the sources of this idea that saltational changes lead to sudden, drastic changes in body plans … but I’m just not seeing that. I am seeing work, for instance, that suggests that Hox duplications have been part of the process of producing additions to body plans, but it’s not a case of “poof, arthropods gain a metathorax in one change” — it’s been quite conventional. It’s more like “poof, arthropods gain an extra Hox gene, which initially adds redundancy and is later shaped by evolutionary processes that confer additional specializations on a segment,” quite ordinary stuff that shouldn’t be at all objectionable to Coyne.
It’s especially peculiar to pin the “hopeful monster” concept on evo-devo, when the one evo-devo expert he quotes, the biologist Sean Carroll, explicitly points out that evo-devo doesn’t support it.
Coyne is also going to be speaking at an evo-devo symposium I’ll be attending in April — I’m going to be very interested to hear what he has to say.
Hagfish are wonderful, beautiful, interesting animals. They are particularly attractive to evolutionary biologists because they have some very suggestive features that look primitive: they have no jaws, and they have no pectoral girdle or paired pectoral fins. They have very poorly developed eyes, no epiphysis, and only one semicircular canal; lampreys, while also lacking jaws, at least have good eyes and two semicircular canals. How hagfish fit into the evolutionary tree is still an open question, however.
