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| An interesting article from Smithsonian today, demonstrating that evolution involves trade-offs. Human Evolution Traded Fur for Sweat Glands—and Now, Our Wounds Take Longer to Heal Than Those of Other Mammals  Even compared to chimpanzees, one of our closest relatives, humans’ scrapes and cuts tend to stick around for more than twice as long, new research suggests I'm sure you realize by now that "research suggests" is a flag that this isn't (yet) a high-confidence finding. That's okay. It doesn't really affect our day-to-day lives, like cancer research or nutrition science. In experiments, human wounds took more than twice as long to heal than those on other mammals—including chimpanzees, which are one of the closest relatives to Homo sapiens. "What's your research about?" "We're going to cut chimps and see how long it takes for them to heal." This is why we have ethics committees, folks. To gather data on the other mammal species, they anesthetized and surgically wounded captive lab mice, rats, olive baboons, Sykes’ monkeys and vervet monkeys. They also studied naturally occurring wounds—mostly caused by fighting—on five captive chimpanzees. In case you were wondering about the ethics. Researchers were not entirely surprised by the results, because skin healing is affected by hair. The follicles at the root of each hair contain stem cells, which, in addition to producing hair, can grow new skin when necessary. Since humans have much less hair than other mammals do, it makes sense that our wounds would also take longer to heal. As we also know by now, just because something "makes sense" doesn't mean it's true. But it does mean possibly less chimp-cutting in the future, because now they don't have to figure out why some result doesn't make sense. “When the epidermis is wounded, as in most kinds of scratches and scrapes, it’s really the hair-follicle stem cells that do the repair,” says Elaine Fuchs, a biologist at Rockefeller University who was not involved with the research, to the New York Times’ Elizabeth Preston. Now, that does raise a couple of questions in my mind. First: humans have places without hair follicles (we have them pretty much all over, but they only produce really thin hair). So what about comparing similar cuts from those places with the hair-having places? Like, we don't have hair follicles on our palms (well... YOU don't), so maybe compare a cut there to one on the forearm, which does have hair? (Unlike other animals, humans can consent to being used in research, up to a point.) Second: humans aren't the only mostly-hairless mammals. Elephants come to mind, though they have a famously thick skin, more resistant to wounds. Seals, whales, hippopatamice, and other aquatic or semi-aquatic mammals are left out of the study. (To be clear, the "aquatic ape" hypothesis has been pretty thoroughly debunked, so no, we're not technically semi-aquatic.) Yes, "hippopotamice" is a made-up plural. I do that sometimes. At some point in the evolutionary journey, humans lost most of their body hair. Eh, as I said, not really; it just... changed. There's also a difference that's correlated, though not perfectly, to natal sex. This is where evolutionary trade-offs come in: whatever the reason for the change (there are hypotheses, my preferred one being sexual selection), if this research is on the right track, the "longer heal time" thing might be a by-product, because it certainly doesn't seem to increase survivability. It also doesn't significantly decrease it, or it wouldn't have happened. One might be tempted to guess that men kept more body hair because early men got injured more than early women, but I'd shy away from such speculation. It’s not entirely clear why early humans lost their hair. But it seems our species swapped the once-abundant hair follicles for sweat glands, which are not as efficient at healing wounds but help keep us cool in hot environments. More evidence for my assertion that humans aren't meant to live in cold environments and that anyone who prefers the cold is an aberration. In theory, this slower wound healing rate should have put humans at a disadvantage. But the researchers speculate that support from friends and family, as well as the use of certain plants as medicine, helped humans survive. And I'm including this bit to support my (more serious) assertion that it's cooperation that got us to where we are today, for better or for worse. And also to address my "doesn't seem to increase survivability" bit above. Though, as noted, it's still speculative. There was a bit of buzz a few months ago, as I recall, when observers saw an orangutan using a medicinal plant; this reminded me of that. Like I said, interesting article and conjectures, despite the animal-rights angle. I'd say I'd like to see more, but while I don't object to eating meat, I feel like the true meaning of the cliché "curiosity killed the cat" is that scientists got out of hand with their curiosity. |
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