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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Bat development

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It always gives a fellow a warm feeling to see an old comrade-in-arms publish a good paper. Chris Cretekos was a graduate student working on the molecular genetics of zebrafish at the University of Utah when I was a post-doc there, and he’s a good guy I remember well…so I was glad to see his paper in Developmental Dynamics. But then I notice it wasn’t on zebrafish—Apostate! Heretic!

Except…it’s on bats. How cool is that? And it’s on the embryonic development of bats. Even cooler! I must graciously forgive his defection from the zebrafish universe since he is working on an organism that is weird and fascinating and important.

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The effect of porn on male fertility

Once again, I bravely plunge into the fascinating world of kinky sex research in humans. This time, we learn something incredibly useful. Gentleman, would you like to know how to improve the potency of your semen? Do you need a good excuse to give your significant other when she catches you browsing porn sites? Do you want another excuse to sneer at those pompous business types who flaunt their fancy cell phones? Here’s the study for you.

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They do everything

By way of Over My Med Body, I found this article that finds new virtues for seafood: it reduces anti-social behavior. This is great news! I plan to announce when I’m feeling cranky here at the Myers household, which will prompt an immediate serving of tasty salmon. I’m going to be eating fish every day!

Well, maybe not…I’m really not that cranky. But it is yet another piece touting the virtues of polyunsaturated fatty acids, especially the essential ω-3 fatty acids in which sea food is rich, so it reinforces my preferences, anyway.

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