Evo-Devo in NYR Books!

This really is an excellent review of three books in the field of evo-devo—

From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design (amzn/b&n/abe/pwll),

Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom (amzn/b&n/abe/pwll), and

The Plausibility of Life:Resolving Darwin’s Dilemma (amzn/b&n/abe/pwll)—all highly recommended by me and the NY Times. The nice thing about this review, too, is that it gives a short summary of the field and its growing importance.

That question of race

John Wilkins has an excellent linky post on the subject of race. My position on the issue is Richard Lewontin’s (seen here in a RealAudio lecture by Richard Lewontin), and more succinctly stated by Wilkins:

So, do I think there are races in biology as well as culture? No. Nothing I have seen indicates that humans nicely group into distinct populations of less than the 54 found by Feldman’s group (probably a lot more – for instance, Papua New Guinea is not represented in their sample set). And this leads us to the paper by the Human Race and Ethnicity Working Group (rare to see a paper that doesn’t list all the authors). They rightly observe that while there are continental differences in genetics, there is no hard division, and genetic variation doesn’t match up with cultural differences per se. There is a genetic substructure to the human population, but it isn’t racial.

Evolving spots, again and again

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a–c, The wing spots on male flies of the Drosophila genus. Drosophila tristis (a) and D. elegans (b) have wing spots that have arisen during convergent evolution. Drosophila gunungcola (c) instead evolved from a spotted ancestor. d, Males wave their wings to display the spots during elaborate courtship dances.

It’s all about style. When you’re out and about looking for mates, what tends to draw the eye first are general signals—health and vigor, symmetry, absence of blemishes or injuries, that sort of thing—but then we also look for that special something, that je ne sais quoi, that dash of character and fashionable uniqueness. In humans, we see the pursuit of that elusive element in shifting fashions: hairstyles, clothing, and makeup change season by season in our efforts to stand out and catch the eye in subtle ways that do not distract from the more important signals of beauty and health.

Flies do the same thing, exhibiting genetic traits that draw the attention of the opposite sex, and while nowhere near as flighty as the foibles of human fashion, they do exhibit considerable variability. Changes in body pigmentation, courtship rituals, and pheromones are all affected by sexual selection, but one odd feature in particular is the presence of spots on the wing. Flies flash and vibrate their wings at prospective mates, so the presence or absence of wing spots can be a distinctive species-specific element in their evolution. One curious thing is that wing spots seem to be easy to lose and gain in a fly lineage, and species independently generate very similar pigment spots. What is it about these patterns that makes them simultaneously labile and frequently re-expressed?

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Evolving spots

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Here’s what seems to be a relatively simple problem in evolution. Within the Drosophila genus (and in diverse insects in general), species have evolved patterned spots on their wings, which seem to be important in species-specific courtship. Gompel et al. have been exploring in depth one particular problem, illustrated below: how did a spot-free ancestral fly species acquire that distinctive dark patch near the front tip of the wing in Drosophila biarmipes? Their answer involves dissecting the molecular regulators of pattern in the fly wing, doing comparative sequence analyses and identifying the specific stretches of DNA involved in turning on the pigment pattern, and testing their models experimentally by expressing novel gene constructs in different species of flies.

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Najash rionegrina, a snake with legs

It’s a busy time for transitional fossil news—first they find a fishapod, and now we’ve got a Cretaceous snake with legs and a pelvis. One’s in the process of gaining legs, the other is in the early stages of losing them.

Najash rionegrina was discovered in a terrestrial fossil deposit in Argentina, which is important in the ongoing debate about whether snakes evolved from marine or terrestrial ancestors. The specimen isn’t entirely complete (but enough material is present to unambiguously identify it as a snake), consisting of a partial skull and a section of trunk. It has a sacrum! It has a pelvic girdle! It has hindlimbs, with femora, fibulae, and tibiae! It’s a definitive snake with legs, and it’s the oldest snake yet found.

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Reinvention

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Forbes magazine asks

What if you could pick one thing and start over from scratch? What would you change? Would you choose another career, a different home, a new spouse? Or would you choose to remake the world around you? Why not fix America’s prison system, make schools more efficient, or make your political leaders more intelligent?

The editors asked me to contribute to their special report, speculating on how we would “reinvent things without regard for cost, politics or practicality”. I thought a little bigger than a new spouse or career, though, and instead tossed in few peculiar ideas about reinventing humanity itself.

How to make a bat

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The relative length of bat forelimb digits has not changed in 50
million years. (a) Icaronycteris index, which is a 50-million-year-old bat fossil. (b) Extant adult
bat skeleton. The metacarpals (red arrows) of the first fossil bats are already
elongated and closely resemble modern bats. This observation is confirmed by
morphometric analysis of bat forelimb skeletal elements.

or•gan•ic | ôr’ganik | adjective. denoting a relation between elements of something such that they fit together harmoniously as necessary parts of a whole; characterized by continuous or natural development.

One of the wonderful things about how development works is that organisms function as wholes, and changes in one property trivially induce concordant changes in other properties. Tug on one element, changing it’s orientation or size, and during embryogenesis any adjacent elements make compensatory adjustments, so that the resultant form flows, fits, and looks organic. This isn’t that surprising a feature of development, though, unless you have the mistaken idea that the genome encodes a blueprint of morphology. It doesn’t; what it contains is a description of interacting agents that work together in a process to produce a complex result. Changes in genes and regulatory elements can essentially produce changes in rules of development, rather than crudely specifying blocks of morphology.

What does this mean for evolution? It means that subtle changes to the rules of development can be caused by small changes to genes (and especially, to regulatory regions of genes), and that the resulting morphological changes may be dramatic, but are still integrated organically into the form of the organism as a whole. Our understanding of how development works is making it clear that large scale macroevolutionary change may be much easier than we had thought.

Here’s an example where this insight is clarifying the evolution of an organism: the fossil record of bats shows an abrupt appearance of fairly sophisticated creatures with elongated digits, clearly capable of gliding or powered flight, with no known intermediates. We expect there were less fully flight-ready predecessors, but fossil preservation is not kind to small, delicate boned animals. It’s also possible that the transitional period was fairly brief; it looks like turning a paw into a long-fingered membranous wing may be a fairly simple change on a molecular level.

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Catfish eating its dinner

John Lynch beat me to this story about catfish feeding on land, so I’ll be brief. It shows how the eel catfish, Channallabes apus, can manage to take an aquatic feeding structure and use it to capture terrestrial meals. Many fish rely on suction feeding: gape the mouth widely and drop the pharyngeal floor, and the resulting increase in volume of the oral cavity just sucks in whatever is in front of the animal. That doesn’t work well at all in the air, of course—try putting your face a few inches in front of a hamburger, inhale abruptly, and see how close you come to sucking in your meal. So how does an aquatically adapted feeder make the transition to eating on land?

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