Don’t miss it! Tonight at 8pmET/7pm Central, NOVA is showing What Darwin Never Knew, a documentary about evo-devo. I shall be glued to my TV tonight!
I just started watching it. So far, it’s a nice little history of Darwin and his ideas; Sean Carroll is a good person to have talking up the story. It’s nothing new yet, and nothing about evo-devo so far — I’m waiting impatiently for it.
Twenty minutes in, we get a little embryology: limb rudiments in snake embryos, tooth rudiments in whale embryos, and branchial arches in human embryos. These are shown as uncompromising evidence of limbed, toothed, and gilled ancestors — cue wails of horror from the Discovery Institute…now.
They also discuss variation in dog breeds. More development, please!
Hmmm. We’re past the half-hour mark, and it’s all selection, selection, selection. It’s clearly explained and it’s a useful intro to the general concept of Darwinian evolution…but I was hoping for something a little more focused and novel. This documentary is supposed to be based on Carroll’s Endless Forms Most Beautiful and The Making of the Fittest, but we’re getting bogged down in very general material and not yet getting to the meat of either book.
Now we’re getting an explanation of DNA sequences as a code (alarms are whooping at the Discovery Institute again), with pigment changes in different varieties of mice as an example. We’re also getting brief mentions of genetic changes that produce color vision and cold-adaptedness in icefish (those are straight from Making of the Fittest).
This bugs me. They’re talking about the number of genes in the human genome as a big surprise — we “only” have 23,000 genes. I don’t know; it always seems to be dropped out of context. How many genes should we have expected?
Some nice animations of transformations of embryos are shown, illustrating (as Haeckel did) that all vertebrates began with a common body plan that diverges in detail over the course of development — I hope an ambulance is on standby in Seattle near the DI.
Unfortunately, they’re using developmental changes as an explanation for why we have too few genes to satisfy our egos. Again, this bugs me: fruit flies and people have comparable numbers of genes, and also comparable developmental processes.
Anyway, it does lead into some useful discussion of evolving pigmentation spots in Drosophila, which leads further into regulatory DNA. Unfortunately, this bit has some confusing stuff. The documentary conflates regulatory DNA with junk DNA — regulatory is not and has not been regarded as junk! — and might lead some viewers into thinking that all junk DNA has developmental functions. It does not.
They do have some nice illustrations of experiments used to tag regulatory sequences with marker genes, making flies with glowing spots on their wings.
Another good example: they’re showing the evolution of regulatory switches in stickleback fish. Cool, it’s David Kingsley! They’re showing how the differences between marine (spiky) and freshwater (non-spiky) is not in the coding sequences of a few genes, but in the regulatory regions of those genes.
Hmm. Repetitive flashy graphics of DNA are beginning to hurt my eyes.
We also get a summary of Tabin’s work on the genes behind different beak morphologies in finches. The same genes are involved, but the differences are in the timing and strength of activation of these genes. The genes involved are also explained as regulatory genes — the genes that switch other genes off and on. This is starting to get into stuff I’d find useful in the classroom.
Hey, now it’s Neil Shubin’s turn to talk about the evolution of limbs. This show is turning out to be a nice introduction to the superstars of evo-devo!
More cool stuff: video from Ellesmere Island, and the discovery of Tiktaalik. Also an amusing animation of the fossil coming to life in Shubin’s lab, which I’m pretty sure doesn’t actually happen.
The show quickly moves from fossils to molecules, and describes efforts to isolate the limb regulatory pathway from modern relatives (paddlefish) of the ancient tetrapods. We get to hear a little bit about Hox genes. Oooh, I could use some of those sequences illustrating the pattern of Hox gene expression in the limb…
We don’t need new genes to make new structures: changing the timing and strength of expression of genes within an existing pathway can create new features.
At least, a clear statement of what Darwin didn’t know that the documentary is describing: we are deriving mechanistic explanations for the processes that produce morphological diversity. It’s a consequence of subtle shifts in the timing and intensity of gene expression in a hierarchy of well-established functional pathways.
We’re getting into the last half-hour here, and the emphasis is switching to humans. Ho-hum. Humans are really crummy experimental models, so I guess we’re not going to get deeper into those mechanisms, but will tap into the audience’s self-centeredness, which they need to do, I guess.
At least they’re focusing a bit: they promise to tell us about the genetics of hand development, and specifically of the thumb. They’re scanning genes that are different between humans and chimpanzees, looking for molecules that suggest they play a role in the differences in digits. A gene is found that is active in the thumb and big toe, and also differs significantly in sequence between us and the chimps. This is work I’m unfamiliar with — it would be nice if they named the gene for us!
Noooo…we’re teased with some interesting work, and now it’s flitting off to talk about the brain.
Another tease: a researcher identifies a gene that differs between humans and chimpanzees, and is defective in humans; it’s involved in chewing muscles. It is suggested that knocking out this gene was part of the process of freeing up the expansion of the cranium. It’s a frustrating part of the medium that it makes it hard to dig up more specific citations. (OK, here’s a short article on Stedman’s work).
They do it again with a regulator of neuronal growth involved in microcephaly: name the gene, please. They keep talking around it, calling it “this gene” or “the key gene”. It’s just odd that they ignore one of the conventions of molecular biology, failing to give us a name that we can use as a handle. It’s going to make it difficult to talk about over the water cooler tomorrow, isn’t it?
Olivia Judson relates it all back to Darwin: he was the beginning, not the end of evolutionary biology.
My opinion overall: the first half hour was boring to me — it was an extremely basic primer in old-school Darwinian biology. The middle hour was of more interest, and did get into real evolutionary developmental biology, and showed off some of the best examples of work in the field. This was the bit I’d find most useful in my classes; that first half-hour was too basic for most freshman biology majors.
I wasn’t too keen on the last bit where it got very human-centric, but I can see where the examples they talked about would provoke viewer interest. I just wish it were possible for the medium to push a little deeper into the topics than they did.
Carroll, Shubin, and Tabin were good. Make them TV stars!