November 7, 2004 - November 13, 2004 Archives
Incidentally, while writing the last post, I stumbled upon the McLean v. Arkansas Documentation Project, a pretty cool resource with lots of material on the case.
You'll remember that the Dover, Pennsylvania School District has decided to include intelligent design in its curriculum. As this story notes, there's some pretty heated complaints in the neighborhood as a result. This story says the Pennsylvania ACLU is looking at the case, but hasn't yet decided what to do. (My own calls to them on the subject were not returned.)
Meanwhile, this editorial by Nancy Snyder seems to argue in defense of science, making the point that the schools should also teach the weakness of intelligent design.
There have long been attempts by evolutionary biologists and evolutionary psychologists to understand just what effect different mating systems have on evolution. Certainly, mating systems in which a male is able to sire many offspring with many different females will cause natural selection to favor different traits than one in which a male is limited to one female. Additionally, a mating system that causes some types of competition to become more extreme can greatly reduce other types of competition. Gorillas, for example, are polygamous, with one male controlling a harem of females to which he has exclusive access. In a situation such as this, there is extreme competition for gaining control of such a harem, but little competition for mating once dominance is established. As a result, there is selective pressure for gorilla males to beat back other males and become dominant, and the results are obvious: gorillas exhibit the greatest sexual dimorphism of any living primate, with males almost twice as large as females. Selection favors the big and brawny types who can successfully fight off their rivals. But there is another form of competition, one in which gorillas aren’t subjected much to – competition between sperm to be the first to reach the egg. There are any number of ways in which sperm from different males can compete, the most obvious of which is through simple quantity. But since male gorillas can be pretty well assured that the females in their harem will mate only with themselves, their sperm has no competition, and it shows when it comes to quantity: male gorillas have the smallest testes to body weight ratio of the great apes. That’s right, the burly boys of the ape world aren’t really packing that much down below, but I still wouldn’t poke fun at them.
You can see how mating systems affect evolution throughout the primate world of which we are a part. Chimpanzees, whose females are very promiscuous, tend to have little sexual dimorphism but a very large testes to body weight ratio. For them, the selective pressure is more heavily focused on post-copulatory sperm competition rather than simple fighting ability. Gibbons, on the other hand, are strictly monogamous. They have little sexual dimorphism and a small testes to body weight ratio. For them, there isn’t much competition to fight off rival males or to thwart rival sperm. We humans seem to be somewhat in the middle, with a moderate amount of sexual dimorphism and a moderate testes to body weight ratio, indicating that during our evolutionary past, we weren’t nearly as monogamous as we’d like to think. But at least we weren’t as slutty as the chimpanzees. (Our lack of total monogamy is corroborated by additional evidence from our genome, some of which Carl Zimmer talks about here.)
Now a new piece of the puzzle has been tossed into the mix, thanks to some new research appearing in Nature Genetics by Steve Dorus and coworkers. The new study, titled “Rate of molecular evolution of the seminal protein gene SEMG2 correlates with levels of female promiscuity” (subscription required), focuses on another facet of sperm competition other than simple quantity. In this case, post-copulatory semen coagulation.
The suit against Cobb County (GA) school district to remove anti-evolution disclaimers from biology textbooks is going well. I was able to attend part of the trial today and saw most of the testimony of CCSD’s lone witness, Dr. George Stickle, who oversees science education for the county. The Discovery Institute is apparently unhappy with the way things are going (Why Isn’t Cobb Co. School District’s Attorney Mounting More Vigorous Defense? and Can Cobb Co. Attorney Overcome Trial Mistakes in Time to Save School District?).
The discovery of Homo floresiensis, the dwarf human species from Flores in Indonesia, has received such massive media attention that creationists have naturally responded to it. Carl Weiland of Answers in Genesis has written an article on Homo floresiensis, and Agape Press has also written an article interviewing AIG's founder, Ken Ham.
AIG basically agrees with the researchers who found the bones (nicknamed 'the Hobbit') that they are a dwarf variety of Homo erectus. However AIG (unlike almost all modern scientists) considers that H. erectus really belongs to H. sapiens, and that the Flores bones should therefore be assigned to H. sapiens too. The human kind, says Wieland, "had a greater range of variation than exhibited today".
That's putting it mildly. If creationists can claim that Homo sapiens and Homo floresiensis belong to the same "kind", on what grounds can they say that australopithecines and H. floresiensis can't also be the same kind, since in its overall body shape floresiensis looks more like an australopithecine than a modern human? In fact, for a while Peter Brown and his team seriously considered placing floresiensis in the genus Australopithecus.
We are all familiar with the idea that there are strikingly different kinds of eyes in animals: insects have compound eyes with multiple facets, while we vertebrates have simple lens eyes. It seems like a simple evolutionary distinction, with arthropods exhibiting one pattern and vertebrates another, but the story isn't as clean and simple as all that. Protostomes exhibit a variety of different kinds of eyes, leading to the suggestion that eyes have evolved independently many times; in addition, eyes differ in more than just their apparent organization, and there are some significant differences at the molecular level between our photoreceptors and arthropod photoreceptors. It's all very confusing.
There has been some recent press (see also this press release from the EMBL) about research on a particular animal model, the polychaete marine worm, Platynereis dumerilii, that is resolving the confusion. The short answer is that there are fundamentally two different kinds of eyes based on the biology of the cell types, and our common bilaterian ancestor had both—and the diversity arose in elaborations on those two types.
Continue reading "Rhabdomeric and ciliary eyes" (on Pharyngula)
A couple of news articles about the upcomming trial of the anti-evolution messages in Cobb County (GA) textbooks:
Use BugMeNot.com if you don’t want to register.
A couple of Discovery Institute links
(I’ve read the brief, and it is bad, very bad. Even cites Behe and Snoke (2004) as research questioning evolution.)