Our Hairlessness: Another Evolutionary Enigma Suggestive of Intelligent Design
Nina Jablonski, Penn State anthropologist and author of Skin: A Natural History, gives an interesting interview to CNN on how our presumed pre-human ancestors lost their fur. It's a bit of a puzzle because (per the conventional set of evolutionary assumptions and deductions) our ancestors were furry like chimps, and Jablonski reasons that they lost their fur so as to allow for improved sweating required by the innovation of our becoming excellent long-distance runners.
CNN: When did we first lose our fur and gain this pigmentation?But as Jablonski also points out, chimps beneath their fur have light-colored skin. Take away the fur and you've a light-colored animal that, in the hot African sun, would be extremely vulnerable to the damaging rays of the sun. So you need dark skin. But what would the evolutionary advantage of that be before the transition to going furless? None that's apparent. So which came first?
Jablonski: The human lineage evolved in Africa. If we start at a starting point of 6 to 7 million years ago, when humans first parted ways from the ancestors of chimpanzees, we have a lot of fossils that indicate that humans were walking on two legs, but they were not modern-looking. They were fairly short, and they still had quite ape-like body proportions: fairly long arms, relatively short legs. These were Australopithecus species of various kinds. They were good bipeds, but they were also capable tree-climbers. But when we look at their skeletons in detail, it's pretty clear that they were not active runners. They could walk on two legs but they weren't running or striding purposefully across the savanna most of the time, they were sort of living lives that are much like those of chimpanzees: fairly close to the edge of the forest, sometimes going into trees for protection, and then walking for short distances in the open to forage.
We hypothesize that, at that stage in our lineage's evolution, we still would have had quite a bit of body hair, because the reason we started to lose body hair is related to the need for controlling body heat.
It turns out that primates lose most of their heat through radiation from the surface of the body into the environment, and by evaporation of sweat. The hotter it is outside, the more important sweat becomes, especially if the animal is exercising vigorously and generating a lot of internal body heat. Internal body heat is good to a point, but you have to be able to liberate excess heat, otherwise your brain, organs and muscles get too hot.
Primates as a lineage almost exclusively use sweating for this purpose (versus other mechanisms such as panting). There have been a lot of hypotheses made about why we lost most of our body hair. And I definitely, and many colleagues of mine definitely are of the opinion -- based on the environmental, anatomical and genetic evidence at hand -- that we lost most of our body hair because of the needs of heat regulation.
The running? But that requires the furless feature (not to mention a massive investment in tightly coordinated anatomical reengineering under the skin, as Ann Gauger discusses in Science and Human Origins). The furless feature then? But that requires the dark skin. OK so the dark skin came first? But that seems to somehow look forward to future usefulness before any evolutionary advantage comes into play, which in turn sounds dangerously teleological.
Darwinian evolution can't just put things like that in the bank, with a view toward their being helpful in some future stage of the evolving lineage. Such anticipation, on the other hand, is a hallmark of intelligent design as we're all familiar with it from daily life. Otherwise, blind Darwinian churning seems to have got very lucky in pulling off these three simultaneous innovations just at the right time, together. That sounds more like an illustration of design innovation, doesn't it?
Image credit: Mark H. Anbinder, Flickr.