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Science Digest

Researchers say a hippo-like mammal known as coryphodon lived in the Arctic 53 million years ago, long before the regional climate cooled.
Researchers say a hippo-like mammal known as coryphodon lived in the Arctic 53 million years ago, long before the regional climate cooled. (American Museum Of Natural History)

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The researchers stressed that they could not conclude with certainty that there is a causal relationship between being sensitive to disgust and being conservative:

"It might be that no simple relationship is there to be found, though it does seem unlikely that political attitudes would shift a person's general emotional disposition, particularly when it comes to disgust, a basic emotion that emerges long before individuals form political attitudes."

-- Rob Stein

Deadly Evolution

The North American short-tailed shrew and the Mexican beaded lizard don't have a lot in common. But don't tell that to their prey.

The two species, one a mammal and the other a reptile, use nearly identical toxins in their saliva to kill other small animals, which they then eat. This unusual example of "convergent evolution" was described at the Society for Molecular Biology and Evolution meeting in Iowa City last week.

The toxins are encoded in two genes, BLTX in the shrew and GTX in the lizard. Each gene is a mutated variant of a gene for a substance called kallikrein, which in turn governs the activity of another biochemical, bradykinin.

When the body releases bradykinin into the bloodstream, arteries dilate, causing blood pressure to drop. The toxins rev up this response to the point where blood pressure falls so low the victim dies of shock.

Yael T. Salzman, a postdoctoral researcher at Harvard University, showed that both BLTX and GTX create the same sort of changes on the cell receptor that processes bradykinin. The toxins expose more fully the place on cells where bradykinin is processed; they guide the incoming molecules; and they make the "active site" more flexible, speeding the reaction.

The thing is, the two toxins reach this common pathway through different mutations in the ancestral kallikrein genes each creature inherited. Death by bradykinin evolved twice.

Salzman is now comparing the genomes of both animals to those of their non-toxic relatives. Small DNA differences function as a molecular clock and may tell her which one evolved the toxin first.

-- David Brown


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