Warring sexes

Both Twisty and Amanda seem a bit weirded out by this news that the fetus can be viewed as a kind of parasite. This story has been around long enough that a lot of us just take it for granted—I wrote about the example of preeclampsia a while back.

There are worse feminist-troubling theories out there, though. In particular, there is the idea of intersexual evolutionary conflict and male-induced harm. In species where there is some level of promiscuity, it can be to the male’s evolutionary advantage to compel his mate to a) invest more effort in his immediate progeny, b) increase her short-term reproduction rate, and c) suppress her ability to mate with other males. After all, his optimal strategy is to flit from female to female, copulate, and put her to work producing his offspring. The female’s preferred strategy, on the other hand, is to take her time, maximize her lifetime reproduction rate, and select the best genetic endowment for her children.

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This sets up a cycle of counter-adaptations in the population. If a male acquires a mutation that increases his fitness at the expense of his mate’s—for instance, if some component of his semen works on her brain to suppress her interest in remating—it will spread through the population due to its positive effect on male fitness, even though it reduces female fitness. Subsequently, a female who acquired a counter-adaptive resistance to the male’s hormonal sabotage would have an advantage, and that gene would spread through the population, reducing male fitness by making them less capable of controlling female reproduction. Then, of course, males could evolve some other sneaky way of maximizing their reproduction rate—vaginal plugs, secretions that make the mated female unattractive to other males, proteins that put her ovaries into overdrive to produce more eggs now at the expense of the female’s long term survival.

It all sounds improbable and dystopian, but all of these mechanisms and more have been observed in that exceptionally promiscuous species, Drosophila. Drosophila seminal fluid has the property of reducing the female’s interest in remating, increasing her rate of egg-laying, and is also mildly toxic. Artificial selection in the lab can produce females that are resistant to the effects, and males that produce more and more potent semen to overcome their resistance, to the point where the line of “super potent” males, when crossed to unselected females, kill their partners with their ejaculations. There is literally a battle of the sexes in these species.

To speak up in my defense, though, not all males are evil exploitive pigs. The logic of this pattern of sexual competitiveness vanishes as species exhibit greater and greater monogamy—if you have only one mate, it is to your advantage to take good care of him or her, because a loss diminishes your reproductive fitness.

Rice WR (2000) Dangerous Liaisons. Proc. Nat. Acad. Sci. USA 97(24):12953-12955.

Rice WR (1996) Sexually antagonistic male adaptation triggered by experimental arrest of female evolution. Nature 381(6579):189-90.

Niobrara

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What do you think of when someone mentions the word “Kansas”? Maybe what leaps to your mind is that it is a farming state that is flat as a pancake, or if you’ve been following current events, the recent kangaroo court/monkey trial, or perhaps it is the drab counterpart to marvelous Oz. It isn’t exactly first on the list of glamourous places. I admit that I tend to read different books than most people, so I have a somewhat skewed perspective on Kansas: the first thing I think of is a magic word.

Niobrara.

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Lamprey skeletons

Bone is a sophisticated substance, much more than just a rock-like mineral in an interesting shape. It’s a living tissue, invested with cells dedicated to continually remodeling the mineral matrix. That matrix is also an intricate material, threaded with fibers of a protein, type II collagen, that give it a much greater toughness—it’s like fiberglass, a relatively brittle substance given resilience and strength with tough threads woven within it. Bone is also significantly linked to cartilage, both in development and evolution, with earlier forms having a cartilaginous skeleton that is replaced by bone. In us vertebrates, cartilage also contains threads of collagen running through it.

These three elements—collagen, cartilage, and bone—present an interesting evolutionary puzzle. Collagen is common to the matrices of both vertebrate cartilage and bone, yet the most primitive fishes, the jawless lampreys and hagfish, have been reported to lack that particular form of collagen, suggesting that the collagen fibers are a derived innovation in chordate history. New work, though, has shown that there’s a mistaken assumption in there: lampreys do have type II collagen! This discovery clarifies our understanding of the evolution of the chordate skeleton.

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Jurassic beaver

Say hello to Castorocauda lutrasimilis, a primitive mammalioform from the middle Jurassic—164 million years ago. Despite its great age, it has evidence of fur and guard hairs still preserved in the fossil, and was rather large for its time. It’s estimated to have weighed about 500g (about a pound) and was over 400mm (over a foot) long in life, and as you can see from the reconstruction, shows signs of being aquatic. In size and lifestyle, it probably resembled the modern platypus.

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Chicken, archosaur…same difference

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My daughter is learning about evolution in high school right now, and the problem isn’t with the instructor, who is fine, but her peers, who complain that they don’t see the connections. She mentioned specifically yesterday that the teacher had shown a cladogram of the relationships between crocodilians, birds, and mammals, and that a number of students insisted that there was no similarity between a bird and an alligator.

I may have to send this news article to school with her: investigators have found that a mutation in chickens causes them to develop teeth—and the teeth resemble those of the common ancestor of alligators and chickens, an archosaur.

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It’s not just the genes, it’s the links between them

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Once upon a time, I was one of those nerds who hung around Radio Shack and played about with LEDs and resistors and capacitors; I know how to solder and I took my first old 8-bit computer apart and put it back together again with “improvements.” In grad school I was in a neuroscience department, so I know about electrodes and ground wires and FETs and amplifiers and stimulators. Here’s something else I know: those generic components in this picture don’t do much on their own. You can work out the electrical properties of each piece, but a radio or computer or stereo is much, much more than a catalog of components or a parts list.

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Electronics geeks know the really fun stuff starts to happen when you assemble those components into circuits. That’s where the significant work lies and where the actual function of the device is generated—take apart your computer, your PDA, your cell phone, your digital camera and you’ll see similar elements everywhere, and the same familiar components you can find in your Mouser catalog. As miniaturization progresses, of course, more and more of that functionality is hidden away in tiny integrated circuits…but peel away the black plastic of those chips, and you again find resistors and transistors and capacitors all strung together in specific arrangements to generate specific functions.

We’re discovering the same thing about genomes.

The various genome projects have basically produced for us a complete parts list—a catalog of bits in our toolbox. That list is incredibly useful, of course, and represents an essential starting point, but how a genome produces an organism is actually a product of the interactions between genes and gene products and the cytoplasm and environment, and what we need next is an understanding of the circuitry: how Gene X expression is connected to Gene Y expression and what the two together do to Gene Z. Some scientists are suggesting that an understanding of the circuitry of the genome is going to explain some significant evolutionary phenomena, such as the Cambrian explosion and the conservation of core genetic processes.

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Welcome, toad overlords

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In yet another example of evolution in action, investigators have documented morphological changes in the cane toads (Bufo marinus) that infest parts of Australia. They’re an invasive species that was introduced in a misbegotten attempt to control beetles that were damaging the sugar cane crop; as it turns out, they are aggressive predators that eat lots of other native fauna, and they secrete toxins that kill animals that try to eat them.

Another feature that contributes to their unwanted success is their rapid dispersal. Individuals can move up to 1.8km per night, occupying new territory at a distressing pace. In the 70 years since they were introduced, they’ve taken over a million square kilometers of Australia. Since dispersal into virgin territories is a significant advantage for the toads, it was predicted that there would be selection for faster migration rates in the population. The authors have several lines of evidence to show that this is the case.

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Eldredge on Darwin

Niles Eldredge has a fine essay online on what it means to be a Darwinist (not the term as caricatured by creationists, but merely as someone who respects the work of Darwin while acknowledging the vast increase in understanding evolution since his time). It’s also useful for explaining how creationists distort the concept of punctuated equilibrium.

The creationists of the day got into the act as well. In a clear demonstration of how thoroughly political the creationist movement has always been in the United States, Ronald Reagan told reporters, after addressing a throng of Christian ministers during the 1980 presidential campaign, that evolution “is a theory, a scientific theory only, and it has in recent years been challenged in the world of science and is not yet believed in the scientific community to be as infallible as it once was believed.” The creationist who managed to get to Reagan’s handlers later bragged to me that those scientists in question were none other than Gould and me. The syllogism ran something like this: (1) Darwin said that evolution is slow, steady, and gradual; (2) some scientists say that evolution consists of rapid bursts of change interrupting vastly longer periods of evolutionary stagnation; ergo, (3) some scientists don’t follow Darwin, meaning (4) some scientists oppose evolution. Then, as now, at least in the public domain, “Darwin” is code for “evolution.” The two are virtual synonyms.

Ain’t that the truth. Darwin is not synonymous with evolution, however, which is why I reject the term “Darwinist” myself. But even so, I’m with Eldredge on this matter: Darwin was an excellent writer and scientist, and his work was the foundation for modern biology.

But I never thought the fact that Darwin—from where I stand as a paleontologist—got some of his story wrong somehow made me an anti-Darwinian. For I have admired the man ever since I took my paperback copy of the sixth edition of On the Origin of Species to read while waiting for Louis Leakey to show up and give a lecture on human evolution on the Columbia campus. I had arrived early to get a good seat, and Louis was late—so I got my first real chance to sample Darwin’s prose. I was fearful of the complexity of the great man’s mind, and of the alien nature of his Victorian prose. But I needn’t have worried, for Darwin proved accessible to the readers of his day—even lay readers—and he remains so today.