Show Me The Science Month Day 9

In what is now central Pakistan, an eight-and-a-half foot long, pregnant aquatic mammal went belly-up, and sank to the bottom of the shallow coastal waters. 47 million years later, a huckster by the name of Duane Gish denied that such mammals ever existed:

There simply are no transitional forms in the fossil record between the marine mammals and their supposed land mammal ancestors . . . It is quite entertaining, starting with cows, pigs, or buffaloes, to attempt to visualize what the intermediates may have looked like. Starting with a cow, one could even imagine one line of descent which prematurely became extinct, due to what might be called an “udder failure” (Gish DT. Evolution: The Challenge of the Fossil Record. El Cajon (CA): Creation-Life Publishers, 1985 p.78-9, quoted at Talk Origins).

Gish may have found it entertaining to imagine what a half-whale, half-buffalo looked like, but today's scientists don't have to imagine the appearance of land-based ancestors of whales. The fossil series leading up to whales tells a very detailed and remarkable story of how furry, four-legged land mammals eventually gave rise to behemoth marine descendants. A spectacular fossil find, reported yesterday in PLoS One, reveals some amazing details from the evolutionary history of whales.



Figure 5A from Gingerich, et al.

Show Me The Science Month Day 8

A tuatara may look like an iguana, but it's a reptile in a category all its own. Tuataras are most closely related to lizards and snakes, but in some ways they are oddballs among reptiles, with unique characteristics among reptiles, like their affinity for cool weather, their nocturnal lifestyle, a third eye on top of the skull, and vertebrae that more closely resemble those of fish and amphibians than reptiles. Male tuataras also have another odd feature - they lack a certain member, which means their reproductive behavior differs from other lizards.


Image courtesy of the Wikipedia Commons

Evolution may be viewed as a controversial subject by much of the US population, but evolutionary biologists frequently complain that this controversy is manufactured by opponents of evolution who have a very flawed understanding of what the science of evolution is. This poor grasp of the science was demonstrated once again in a talk given by Intelligent Design advocate Jonathan Wells, who claims that "DNA does not control embryo development."

Wells, who has a PhD in biology, (I don't know what the director of graduate studies at UC Berkeley was smoking), has repeatedly demonstrated his cluelessness about basic elements of biology, and he is a clear illustration of why a PhD does not necessarily indicate anything about its holder's knowledge. Over at Pharyngula, PZ Myers has a thorough takedown of Wells' absurd talk. The talk is based on the bizarre claim that "DNA does not control embryo development." If that's true, Wells argues, then the whole tottering neo-Darwinian edifice collapses, or something like that.

Show Me The Science Month Day 7

The birth of new species always involves a barrier to cross-breeding between two different groups of the same species. This barrier may start out as a geographical barrier (two raccoon populations on different sides of a mountain never encounter each other and thus fail to interbreed), but however it starts, reporductive barriers always turn into a genetic barrier. To form new species, two populations of organisms have to drift apart genetically.

The genetic split can happen in a variety of ways, as scientists are discovering in the their quest to find 'speciation genes.' It can happen because a selfish gene fails to be shut down in the offspring of cross-breeding flies, and it can happen because one mouse gene doesn't work right when it encounters genetic variants from another subspecies.

A report in Science describes one more speciation gene, this time in two sub-species of thale cress plants. In this case, the barrier to reproduction is the result of faulty gene copying.

Show Me The Science Month Day 6

Yesterday we discussed the discovery of a gene that keeps mouse subspecies from producing fertile hybrid offspring. In other words, a gene that is putting a reproductive barrier between incipient mouse species.

Scientists have discovered speciation genes in other organisms as well. A report by Nitin Phadnis and H. Allen Orr at the University of Rochester describes a speciation gene that puts a reproductive barrier between fruit fly subspecies.