Ambergris!

i-3acd10441ccbd97ee2c56e30e728bc88-ambergris.jpg

Majikthise reports that an Australian couple has found a $295,000 lump of ambergris on a beach. Ambergris is cool stuff, so let me add to it’s splendor by bringing up two scientific views of it.

First, let’s hear from the chemists:

Since ancient times, ambergris has been one of the most highly valued perfumery materials. It is secreted in the stomach or intestinal tract of the sperm whale and released into the sea in the form of a grey to black stone-like mass. When exposed to sunlight, air and sea water, the material gradually fades to a light grey or creamy yellow colour and, at the same time, the main component, the odourless triterpene alcohol ambrein, is oxidatively degraded. Some of the products resulting from this chemical process are responsible for the organoleptic properties of ambergris.

We know the chemical structure of many of the active components of ambergris—it’s a beautifully complex collection of compounds.

i-065e851613a76197ebdfdef70a558f61-ambrein.gif
Two ambergris odorants and their natural precursor, ambrein (1).
i-2a7c30bee14469c3a9a716f14a476dc6-ambrein_derivatives.gif
Examples of non-trans-decalin ambergris odorants.

And what about us biologists?

The effect of ambrein, a major constituent of ambergris, was studied on the sexual behavior of male rats. The rats were administered ambrein in doses of 100 and 300 mg/kg body weight. Male sexual activities were assessed by recording the erectile responses (penile erection) and homosexual mountings in the absence of female. The copulatory studies were carried out by caging males with receptive females brought into estrus with subcutaneous injections of estradiol benzoate and progesterone. The copulatory pattern of treated male rats (mountings, intromissions, ejaculations and refractory period), the pendiculations (yawns/stretches) and orientation activities towards females, the environment and themselves, were recorded. Ambrein produced recurrent episodes of penile erection, a dose-dependent, vigorous and repetitive increase in intromissions and an increased anogenital investigatory behavior, identifying the drug used in the present study as a sexual stimulant. It is conceivable from the present results that the ambrein-modified masculine sexual behavior in male rats supports the folk use of this drug as an aphrodisiac.

Mmm-mmmm. Good stuff, that ambergris.

Gorbachov M.Yu., Rossiter K.J. (1999) A New Electronic-Topological Investigation of the Relationship between Chemical Structure and Ambergris Odour. Chem. Senses 24:171-178.

Taha SA, Islam MW, Ageel AM (1995) Effect of ambrein, a major constituent of ambergris, on masculine sexual behavior in rats. Arch Int Pharmacodyn Ther 329(2):283-94.

A few links to delightful anti-ID pieces

Some good news first: Dembski gave a talk in Kansas. Kansas! You’d think they’d love him there, but his audience was better informed than you might expect, from the example of their elected Board of Education officials.

Dembski, who may have been led to expect a warmer reception for his ideas—he was in Kansas, after all—seemed to grow testy as questioner after questioner expressed doubt about his assertion that evolution is a failed theory and that patterns in nature are best explained as a result of intelligence.

I know there is a solid body of intelligent, well-informed people in Kansas, and the escapades of the klutzes trying to railroad the state back into the Middle Ages are probably rousing quite a bit of antagonism. I also suspect the Discovery Institute schtick is getting old, and since Intelligent Design is a proven loser in the courtroom, its fans are looking for a new angle. The DI Fellows might want to think about revamping their CVs.

The New York Times once again screws up by asking a religion writer to comment on evolution, and of course she casts it all in religious terms, opting in to Ruse’s terrible characterization of it as “evolutionism”. Fortunately, John Rennie has ripped into that claim satisfyingly.

Shulevitz and Ruse can go on about “evolutionism” if they like, but the kinds of claims they find troubling have nothing to do with what would be taught in public school science classes. Thus their arguments might be relevant as social context, but they have no bearing on any of the specific disputes involving whether or how evolution should be taught. Whether Shulevitz and Ruse would want this to be the case, their arguments help the creationists distract the public from the real issues.

Chris Mooney also has some good criticisms of the piece, although he and I do disagree on strategy (I think promoting secularism, of which atheism is a part, is a necessary component of any long term resolution of the creationism problem, and that is not the same as this mythical “evolutionism”.)

There is this fellow, Krauze, who runs some forgettable Intelligent Design blog, who can be best described as polite, persistent, and utterly clueless. He’s been having a little back-and-forth with Jason Rosenhouse (who has a more patient temperament than I do, clearly), and Jason neatly polishes off Krauze’s claim that ID just needs more time to develop. It’s entertaining and thorough.

Yearly Kos

The speakers for the science panel at the Yearly Kos convention have been announced, and they are Chris Mooney, some goofy guy named PZ, and Wendy Northcutt. We’re going to Vegas! Since I only drink in moderation, never gamble, and the only showgirl I want to see is my wife (who will be coming along), I’m not going to have much to do other than castigate wobbly Democrats, and maybe argue with those annoying progressive Christians. There better be some firebreathing, let me tell you…the only magic show I want to see is a bunch of Democrats with spines, and skip the animal tamers—I want to see some fierce beasts breaking loose.

Vertebral variation, Hox genes, development, and cancer

i-ccbc028bf567ec6e49f3b515a2c4c149-old_pharyngula.gif

First, a tiny bit of quantitative morphological data you can find in just about any comparative anatomy text:

mammal number of vertebrae
cervical thoracic lumbar sacral caudal
horse 7 18 6 5 15-21
cow 7 13 6 5 18-20
sheep 7 13 6-7 4 16-18
pig 7 14-15 6-7 4 20-23
dog 7 13 7 3 20-23
human 7 12 5 5 3-4

The number of thoracic vertebrae varies quite a bit, from 9 in a species
of whale to 25 in sloths. The numbers of lumbar, sacral, and more caudal vertebrae also show considerable variation. At the same time, there is a surprising amount of invariance in the number of cervical vertebrae in mammals — as every schoolkid knows, even giraffes have exactly the same number of vertebrae in their necks as we do. What makes this particularly striking is that other vertebrates have much more freedom in their number of cervical vertebrae; swans can have 22-25. I was idly wondering why mammals were so limited, and stumbled onto a couple of papers that addressed exactly that question (Galis & Metz, 2003; Galis, 1999). Galis’s explanation is that it is a developmental constraint that may have something to do with the incidence of cancer.

Development is an intricately choreographed process that treads a dangerous line. On one side is stability; but development is in many ways a destabilizing process, in which cells have to change their path and form new tissues, and stability is not compatible with it. On the other side is chaos, unregulated proliferation — cancer. During development, the organism has to foster proliferation and change to a greater degree than it can tolerate later, and that loosening of constraints represents a danger. Galis suggests that one reason we mammals may always have 7 cervical vertebrae is that the regulatory genes that specify the number of vertebrae are coupled to processes that otherwise regulate cell fates, and that modifications to those genes that would cause variation in vertebra number would also lead to unacceptable increases in the frequency of embryonal cancers.

This isn’t at all an improbable idea. Genes exhibit bewilderingly complex patterns of expression, and pleiotropy (the regulation of multiple phenotypic characters by a single gene) is the rule, not the exception. The Hox genes, the particular genes that control the identity of regions along the length of the animal, are known to switch on and off in proliferating mammalian cell lines in culture. Perhaps the Hox genes involved in defining cervical vertebrae are somehow also involved in controlling cell proliferation, making them dangerous targets for evolution to tinker with?

Galis provides several lines of evidence that this is the case. To see whether variation in cervical vertebra number leads to increased incidence of cancer, we need to look for instances of variation in mammalian vertebrae.

There isn’t much variation in cervical vertebra number, though. There is an exception: sometimes, the 7th cervical vertebra is found to undergo a partial homeotic transformation and forms a pair of ribs, which are normally found only on thoracic vertebrae. Humans develop cervical ribs with a frequency of about 0.2%; do they also develop cancers? The answer is yes, with a frequency 125 times greater than the general population.

Another place to look would be in phylogenetic variation — between groups rather than within a population. It turns out that there are two groups of mammals that do have a non-canonical number of cervical vertebrae: one manatee genus and two genera of sloths. No data is available on frequencies of embryonal cancers in either, and Galis reports that manatees at least seem to have a low incidence of cancer. One explanation is that both sloths and manatees have exceptionally slow metabolic rates, which in itself will reduce the frequency of cancer, since it will reduce the rate of oxidation damage; the idea is that this low cancer rate may have made these organisms more tolerant of variation in these genes.

An open question is how birds can have greater variability in the number of cervical vertebrae — they certainly don’t have low metabolic rates. One suggestion is that the coupling between these particular Hox genes and a predilection for cancer is unique to mammals. Another possibility is that birds possess other, unidentified mechanisms that reduce free radical production, reduces oxidative damage, and makes them relatively cancer-free. Galis cites several studies that show that birds do seem to be less severely afflicted with cancers than us mammals.

It’s an interesting idea, but the evidence so far is a collection of correlations. I’d be interested in seeing some direct analyses of the role of patterning genes on carcinogenesis. Still, it’s the first answer I’ve seen to explain why such a peculiar restriction in morphology should be nearly universal within a whole class of animals, when other classes allow so much more diversity.

i-a288d57171e0fe2576d6ce35a0930a2e-camelskel.jpg

Galis, F and JAJ Metz (2003) Anti-cancer selection as a source of developmental and evolutionary constraints. BioEssays 25:1035-1039.

Galis, F (1999) Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes, and cancer. J Exp Zool (Mol Dev Evol) 285:19-26.

The DI can’t get anything right?

A few months ago, after learning that Bill Gates was giving money to the Cascadia branch of the Discovery Institute (which studies transportation issues in the Pacific Northwest), I wondered if the DI was as incompetent and delusional about transportation as evolution. Here’s one answer—not surprisingly, they may again be tools of interests opposed to real advances. I am not by any means an informed expert on these issues, but I do know the Seattle area desperately needs better mass transit—I have seen rush hour on I5, and do not know how people can stand it—yet what the DI offers is a distracting welter of speculative and untried ideas that seem calculated more to muddy the waters and preserve the profitably wasteful status quo than anything else.

A typical right-wing think-tank, in other words.

Castrating trematodes!

Since I mentioned yesterday that penis size mattered, upon stumbling on this article about the horrific effects of a trematode infestation, I thought everyone might enjoy a grim and vivid picture of what trematodes can do to a poor, innocent mollusc.

This is a photo of a trematode, or fluke. Trematodes are parasitic flatworms with very complex life cycles; this particular one is a cercaria, or tailed larva. They swim about and infest various hosts at various stages, proliferating and spreading through tissues, before moving on to infect the next host in their cycle.

i-3904fbc02f39800245e7aa9178db483f-neophasis.jpg

[Read more…]

Vonnegut. And so it goes.

Alas, my daughter and I are big fans of Vonnegut’s writing, but he’s showing signs of losing it. He sounds terribly unhealthy on the radio, and his performance on the Daily Show a while back was depressing. This morning, Vonnegut was on NPR, and said scientists were defending evolution because of “tribalism”, and that “my body and your body are miracles of design”, and that “natural selection couldn’t possibly have produced such machines.” Please, please remind me to stop blogging when my mind deteriorates that far, OK?

To call the body a “miracle of design” is begging the question, while denying the possibility of evolution is the argument from incredulity. Neither is at all persuasive. I would like to know if Vonnegut thinks all those scientists who insist that the Earth is roughly spherical are also arguing for tribal dogma, or whether he suspects that they might actually be relying on this little thing called evidence…and why he thinks biologists fall in the former category and not the latter.

Out of respect for his past writing career, though, I will refrain from cutting him up with a razor here. There were some signs in his interview that he hasn’t drunk deep of the ID kool-ade, but overall it was a sadly muddled exercise in sloppy reasoning, spoken without the sharpness and clarity I’ve expected from Vonnegut.