Chelifores, chelicerae, and invertebrate evolution

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One of the most evocative creatures of the Cambrian is Anomalocaris, an arthropod with a pair of prominent, articulated appendages at the front of its head. Those things are called great appendages, and they were thought to be unique to certain groups of arthropods that are now extinct. A while back, I reported on a study of pycnogonids, the sea spiders, that appeared to show that that might not be the case: on the basis of neural organization and innervation, that study showed that the way pycnogonid chelifores (a pair of large, fang-like structures at the front of the head) were innervated suggested that they were homologous to great appendages. I thought that was pretty darned cool; a relic of a grand Cambrian clade was swimming around in our modern oceans.

However, a new report by Jager et al. suggests that that interpretation may be flawed, and that sea spider chelifores are actually homologous to the chelicerae of spiders.

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Ask me a question!

The new “Ask a Science Blogger” question of the week is…

“Since they’re funded by taxpayer dollars (through the NIH, NSF, and so on), should scientists have to justify their research agendas to the public, rather than just grant-making bodies?

NO. No way.

The public has no context in which to understand most research programs and aren’t at all qualified to assess a grant proposal. This would be an invitation to the ignorant to proxmire good research. Can you imagine how the creationists would react to proposals in evolutionary biology? Or cat lovers to experimentation on animals?

On the other hand, I do think that researchers have an obligation to educate the public about how they are using federal funds. They don’t have to justify, but they should explain. It might be a useful condition of a grant to require that the recipient give an open lecture summarizing in terms a non-specialist can understand the results of their work, at the end of the grant period.

That great and arbitrary abortionist in the sky

Great stuff from Majikthise,
Pandagon, and
Shakespeare’s Sister on this fairly obvious paper (pdf) that argues that the rhythm method kills more embryos than contraceptives. It’s straightforward: by avoiding sex during the prime time for ovulation and fertilization, there’s a greater likelihood of fertilization occurring when the egg is past its sell-by date…it’s increasing the chance of spontaneous abortion and birth defects. The paper is all speculative and philosophical about it all, but there are actually some suggestive epidemiological data that suggest it is true. A study by Jongbloet describes a doubling of the frequency of Down Syndrome in young Catholic mothers. Gray and Kambic say:

There is an excess of male births conceived during the least fertile days, and the risk of spontaneous abortion doubles outside the period of peak fertility. Furthermore, there is growing but inconclusive evidence linking chromosome abnormalities to aged gametes.

(I have to offer a few caveats. There are also studies that report no deleterious effect of the rhythm method, and I also suspect that studies that show a change in viability are more likely to be published than those that don’t—that file drawer effect. But when the Bovens paper says there is no empirical evidence for his speculation that conception outside a “heightened fertility” interval would be more likely to be problematic, it’s not quite right.)

I think the argument is a little bit irrelevant for the same reason Amanda states: pregnancies fail all the time anyway, even if the eggs are fertilized at the optimum time. Trying to get pregnant is always going to be an exercise in baby killing, if you believe that a freshly fertilized zygote is a a fully fledged human being—that baby is going to get flushed spontaneously about half the time.

I’m guessing how the anti-choice crowd will react to this idea.

  • Simple denial. They’ll ignore the argument every time it is made.
  • Protestations of disbelief and ignorance. This is an abstract argument from probability and statistics, after all—it will make no impression on the innumerate.
  • You may not believe this, but there are lots of people who flat out disbelieve that randomness exists. Everything is fixed and fated. Probability arguments are meaningless.
  • The responsibility is God’s. You see, contraception and abortion by a woman means she is abrogating God’s privilege. Leaving it up to chance (which doesn’t exist, see above) is putting the decision in God’s hands…and if God decides to take the zygote to heaven, that’s his right.

That last argument is the interesting one. If we accept the anti-choicer’s claim that the zygote is a baby at the moment of fertilization, and the abortion rate is about 46 million per year world wide, and the number of live births is approximately equally to the number of spontaneous abortions, and the number of babies born last year was about 80 million…that means God killed almost twice as many babies as the abortionists did last year. That psychopathic bastard.

I want to see the anti-choicers start picketing churches instead of abortion clinics.

Oh, and there’s one more strategy they could take: this result says that all contraception is evil and must be forbidden. There’s already an attitude among some nuts that all sexual activity must be accompanied by the possibility of procreation, so why not go whole hog and ban the rhythm method, too?

Jongbloet PH (1985) The ageing gamete in relation to birth control failures and Down syndrome. Eur J Pediatr 144(4):343-7.

Gray RH, Kambic RT (1988) Epidemiological studies of natural family planning. Hum Reprod 3(5):693-8.

“Here in the North there is no such thing as monkeys.”

OK, Canadians, ‘fess up. I know you guys are so danged nice and polite…this is just an attempt to make your Southern neighbor feel less uniquely stupid, isn’t it? You put up some obliging Québécois Inuit Pentecostals to pretend to be as dumb as a Kansas preacher, didn’t you?

“If the town complains and says no, the committee can ask the principal or the director of teachers to approach the teacher and say, ‘Look, this is not the subject to be taught here in this town, or in this place, because we know we have been humans from the beginning, ‘” said Molly Tayara.

“I don’t personally accept my children being taught that they came from some species from Africa somewhere.

“Here in the North there is no such thing as monkeys.”

(via Josh)

Carnivalia, and an open thread

Read and discuss:

Or talk about anything you want. The pope’s presence annihilates ice cream and tampons. Bill Frist really needs to take a shower before working in the Senate. What kind of penalties would be appropriate for Kenny Boy? I’m sure you can all think of something to talk about—I’m buckling down for a few hours to finish reviewing a paper.