Evolution of Hormone Signaling

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Last week, I received some delusional e-mail from Phil Skell, who claims that modern biology has no use for evolutionary theory.

This will raise hysterical screeches from its true-believers. But, instead they should take a deep breath and tell us how the theory is relevant to the modern biology. For examples let them tell the relevance of the theory to learning…the discovery and function of hormones…[long list of scientific disciplines truncated]

Dr Skell is a sad case. He apparently repeats his mantra that biology has no need of evolution everywhere he goes, and has never bothered to actually crack a biology journal open to see if biologists actually do use the theory. In my reply to him, I did briefly list how evolution is used in every single one of his numerous examples, but today I’m going to focus on just the one I quoted above: hormones.

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Octopus brains

Once upon a time, as a young undergraduate, I took a course in neurobiology (which turned out to be rather influential in my life, but that’s another story). The professor, Johnny Palka, took pains at the beginning to explain to his class full of pre-meds and other such riff-raff that the course was going to study how the brain works, and that we were going to be looking at invertebrates almost exclusively—and he had to carefully reassure them that flies and squid actually did have brains, very good brains, and that he almost took it as a personal offense when his students implied that they didn’t. The lesson was that if you wanted to learn how your brain worked, often the most fruitful approach was an indirect one, using comparative studies to work out the commonalities and differences in organization, and try to correlate those with differences and similarities in function.

At about that time, I also discovered the work of the great physiologist, JZ Young, who had done a great deal of influential work on the octopus as a preparation for studying brain and behavior. (Young, by the way, went by the informal name “Jay-Zed”, and there you have another clue to my affectation of using my first and middle initial as if it were a proper name.) It was around then that I was developing that peculiar coleoideal fascination a few of the readers here might have noticed—it was born out of an appreciation of comparative biology and the recognition that cephalopods represented a lineage that independently acquired a large brain and complex behavior from the vertebrates. To understand ourselves, we must embrace the alien.

Young’s attempts to understand mechanisms of learning in memory in the octopus were premature, unfortunately—they have very complex brains, and we made much faster progress using simple invertebrates, like Aplysia, to work out the basics first—but it’s still the subject of ongoing research. I was very pleased to run across a general overview of the octopus brain in The Biological Bulletin.

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The burden of bearing a massive penis

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Maybe half of my audience here will be familiar with this problem. You’re a man, and you’re hauling this massive, ummm, package around in your pants everywhere you go. Other men fear you, while the women worship you…yet at the same time, your e-mail is stuffed to bursting with strange people making friendly offers to help you make it even bigger. It’s a dilemma; you think you would be even more godlike if only it were larger, but could there possibly be any downside to it? (There is a bit of folk wisdom that inflating it drains all the blood from the brain, but this is clearly false. Men who are stupid when erect are also just as stupid when limp.)

A couple of recent studies in fish and spiders have shown that penis size is a matter of competing tradeoffs, and that these compromises have evolutionary consequences. Guys, trash that e-mail for penis enlargement services—they can make you less nimble in pursuit of the ladies, or worse, can get you killed.

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Acoelomorph flatworms and precambrian evolution

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One of many open questions in evolution is the nature of bilaterian origins—when the first bilaterally symmetrical common ancestor (the Last Common Bilaterian, or LCB) to all of us mammals and insects and molluscs and polychaetes and so forth arose, and what it looked like. We know it had to have been small, soft, and wormlike, and that it lived over 600 million years ago, but unfortunately, it wasn’t the kind of beast likely to be preserved in fossil deposits.

We do have a tool to help us get a glimpse of it, though: the analysis of extant organisms, searching for those common features that are likely to have been present in that first bilaterian; we’re looking for the Last Common Bilaterian by finding the Least Common Denominators among living species. And one place to look is among the flatworms.

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Old spiders

Two short articles in this week’s Science link the orb-weaving spiders back to a common ancestor in the Early Cretaceous, with both physical and molecular evidence. What we have is a 110-million-year-old piece of amber that preserves a piece of an orb web and some captured prey, and a new comparative study of spider silk proteins that ties together the two orb-weaving lineages, the Araneoidea and the Deinopoidea, and dates their last common ancestor to 136 million years ago.

Araneoids and Deinopoids build similar looking webs—a radial frame supporting a sticky spiral—but they differ in how they trap prey. Deinopoids spin dry fibers that they fluff into threads that adhere electrostatically to small insects; Araneoids secrete glue onto the the strand, which takes less work (no fluffing), and is much more strongly adhesive. The differences are enough to make one question whether there was a single origin of orb weavers, or whether the two groups independently stumbled on the same efficient form of architecture.

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Deep homologies in the pharyngeal arches

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PvM at the Panda’s Thumb has already written a bit about this issue in the article “Human Gland Probably Evolved From Gills”, but I’m not going to let the fact that I’m late to the party stop me from having fun with it. This is just such a darned pretty story that reveals how deeply vertebrate similarities run, using multiple lines of evidence.

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Polar lobes and trefoil embryos in the Precambrian

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The diagram above shows the early cleavages of the embryo of the scaphopod mollusc, Dentalium. You may notice a few peculiarities: the first cleavage is asymmetric, producing a cell called AB and a larger sister cell, CD. Before the second division, CD makes a large bulge, called a polar lobe, and it almost looks like it’s a three-cell stage—this is called a trefoil embryo, and can look a bit like Mickey Mouse. The second division produces an A, a B, a C, and a D cell, and there’s that polar lobe, about as large as the regular cells, so that it now resembles a 5-cell embryo. What’s going on in these animals?

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Evolution and homosexuality

Seed has an interview with Joan Roughgarden, somewhat controversial evolutionary biologist and author of Evolution’s Rainbow : Diversity, Gender, and Sexuality in Nature and People(amzn/b&n/abe/pwll). Here’s the short summary of her basic thesis:

Joan Roughgarden thinks Charles Darwin made a terrible mistake. Not about natural selection–she’s no bible-toting creationist—but about his other great theory of evolution: sexual selection. According to Roughgarden, sexual selection can’t explain the homosexuality that’s been documented in over 450 different vertebrate species. This means that same-sex sexuality—long disparaged as a quirk of human culture—is a normal, and probably necessary, fact of life. By neglecting all those gay animals, she says, Darwin misunderstood the basic nature of heterosexuality.

Roughgarden is an awkward case that provokes a difficult split in people’s opinions. She is 100% right that homosexuality is common and that its prevalence ought to be regarded more seriously as an indication of an interesting and enlightening phenomenon in evolution. However, she’s completely wrong in rejecting sexual selection: in rejecting a simplistically heterosexual view of nature she swings too far the other way, adopting a simplistically homosexual view instead of a messy, complex, and almost certainly more correct mixed view. She’s rather superficial in her treatment of Darwin. And most annoyingly, she has a bad habit of playing the transgender card and accusing her critics of disagreeing with her because of some LGBT bias.

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Clausen, Keck, Hiesey

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To continue a bit of theme, I mentioned that there were some different ways to approach biology, and that old-school systematists with their breadth of knowledge about the diversity of life are getting harder and harder to find. This is something I also bring up in my introductory biology course, where we discuss how biologists do their work, and I mention that one distinction you can find (which is really a continuum and frequently breached) is that there are bench scientists and field scientists, and they differ in multiple ways. Bench scientists tend to be strongly reductionist, tend to focus on one or very few species, and may study just one specific, highly inbred lab strain of a species, and try to minimize environmental variables. Variation is noise that interferes with getting at basic mechanisms. Field scientists, on the other hand, argue that the simplicity of the lab is unrealistic, that the proper study of organisms has to be done in the messy complexity of the real world, and think that variation, rather than being uninteresting noise, is fascinating stuff, the meat and potatoes of evolution. Both points of view have their place, and speaking for all biologists, I think we appreciate the power and necessity of both approaches. The money seems to mostly go to the bench guys, though, which does unfortunately skew the field as a whole.

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