The Science, the Silly and the Serious (20 July 2010: evening)

The silly: the Boulder City council doesn’t care if a woman gardens in her gloves and thong bottom (only) but doesn’t want you addressing the council in your underwear:

The days when a citizen could address the Boulder City Council wearing only underwear may be over.

The council will vote on new decorum rules in September, seven months after a resident stepped up to a microphone in his boxers.

The rules were already under review, but that incident led to a proposed ban on undressing during meetings. […]

But the council declined to outlaw topless females, despite complaints about a woman who gardens in a thong and gloves.

The science: what is behind the skin color in the skin that you show (excepting Rep. John Boehner)? It isn’t as easy a question to answer as you might think:

These differences among populations almost certainly represent more than one evolutionary event. First, although we don’t have fossil skin from our African hominin ancestors like Homo erectus, it’s likely that they were dark, as are African populations now. But even earlier ancestors may have been lighter. If you look at our closest relatives, chimps and gorillas, you see that their skin (at least those parts under the hair) is unpigmented. Only the exposed parts are pigmented. The ancestral color of humans, then, was probably light (but not as light as, say, Swedes) and then, as we became “naked apes,” evolved to a darker shade. (The evolution of hairlessness in our species is another matter, perhaps involving our ability to sweat.)

Then, as the presumably dark populations of humans moved into the Middle East and Europe, they evolved lighter skin color. But when those populations colonized Australia, skin color got dark again. This almost certainly happened, too, when humans moved from northern Asia across the Bering Strait and down into the Americas: those populations that reached Central and South America likely re-evolved dark pigmentation.

What were the selective pressures that caused these changes? For a long time I accepted the “classic” story that was taught in school: populations getting more sunlight evolved darker skin as protection against UV-induced melanomas and the toxic effects of too much vitamin D3, which is produced only by sunlight striking the skin. In low-light areas, skin evolved a lighter shade because we need fair amounts of vitamin D3 to build strong bones (without it, children get rickets, which is why foods like milk often have added vitamin D). Thus, dark-skinned ancestors in the tropics would have reduced vitamin D toxicity and fewer melanomas, while lighter ancestors in the temperate zones would have stronger bones. This could cause differential mortality or reproduction that would explain the differences in pigmentation.

The problem with this story is just that—it’s a story. Although this scenario sounds plausible, there wasn’t much hard evidence supporting it, at least not when I was in school. A recent paper in PNAS by Nina Jablonski and George Chaplin summarizes the latest evidence and comes to some different conclusions about the evolution of human skin color.

Surf to the link to find out what those conclusions are, and what Jerry Coyne thinks of them. Evolution isn’t easy!

The serious It sure appears that President Obama screwed up by being too eager to fire Shirley Sherrod; he fell for the heavily edited video which appeared to show her not doing her best to help a white farmer with his financial situation because of his race.

In fact, these clips were taken out of context from a longer video in which she made the point that we need to move beyond race:

Admit the mistake, Mr. President.

July 21, 2010 Posted by | Agricultural Commisioner, Barack Obama, evolution, humor, nature, politics, politics/social, racism, science, WTF | Leave a comment