Waste Heat II: Some Like It Hot
xuenay links to Gregory Cochran's writings on difference in mutational load in the tropics and the temperate regions. Apparently mutations happen more quickly in higher temperatures (why?) and since most mutations are harmful and the brain is the most easily-harmed organ in the body, we would expect higher-temperature regions to produce less efficient brains. If brains are less efficient, it's less valuable to have them and we could expect them to be smaller; this provides an alternative (and better) explanation for variation in cranial capacity (and IQ) with latitude.
alicorn24 points out that mammalian diving reflex explains why cold water on the face is invigorating better than a selective brain cooling explanation. We were discussing last night whether cold water on any other part of the body, or cold air on the face, or any other combination other than water + face, was also invigorating and settled on "Um, maybe?". Also, does cold water to the face really only work at < 70 degrees F? And does rubbing a little bit on from the sink really trigger the diving reflex?
I am willing to retract my claim that waste-heat dissipation explains the latitude-IQ gradient in favor of Cochran's much superior theory, and say diving reflex probably explains away cold water to the face, but I'm not quite abandoning the rest of the theory - yawning, boredom and tiredness - just yet.