In a previous post, I discussed how John Eiler and his team from Caltech were using the clumping patterns of carbon-13 and oxygen-18 to determine the internal temperature of extinct animals. Briefly, the two isotopes clump together in materials that were formed at lower temperatures. The degree of clumping indicates the temperature at which the material formed.
Now the researchers, led by Benjamin Passey (currently at Johns Hopkins University), are applying the same technique to examine minerals in soil buried in the Turkana Basin region of northern Kenya, the cradle of human evolution. Today, that region is one of the hottest on Earth. Scientists have speculated that if the area were equally hot a few million years ago, that could explain why humans evolved such traits as bipedalism and hairlessness. Both would be adaptations to excessive heat. An upright, bipedal stance limits exposure to both the hot ground (which can be appreciably hotter than the surrounding air) and to the sun’s rays (which strike a smaller cross-section of an upright body).
It turns out that the soil temperature back then was often above 35 °C. (95 °F.). This lends credence to the theory that many human traits evolved as adaptations to cope with heat.
You can hear John Eiler discuss his work here.