The first (here) is a review by Steven Mithen (SM) of a new book on human brain size. The received wisdom has been that human brains are large compared to our body size. The SM review argues that this is false. The book by Suzana Herculano-Houzel, a neuroscientist from Brazil, makes two important points (and I quote):
(i) What is perhaps more astounding than that number itself, one that is actually less than the often assumed 100 billion neurons, is that 86 billion makes us an entirely typical primate for our size, with nothing special about our brain at all, so far as overall numbers are concerned. When one draws a correlation between body mass and brain mass for living primates and extinct species of Homo, it is not humans—whose brains are three times larger than those of chimpanzees, their closest primate relative—that are an outlier. Instead, it is the great apes—gorillas and the orangutan—with brains far smaller than would be expected in relation to their body mass. We are the new normal in evolution while the great apes are the evolutionary oddity that requires explanation.
(ii) But we remain special in another way. Our 86 billion neurons need so much energy that if we shared a way of life with other primates we couldn’t possibly survive: there would be insufficient hours in the day to feed our hungry brain. It needs 500 calories a day to function, which is 25 percent of what our entire body requires. That sounds like a lot, but a single cupful of glucose can fuel the brain for an entire day, with just over a teaspoon being required per hour. Nevertheless, the brains of almost all other vertebrates are responsible for a mere 10 percent of their overall metabolic needs. We evolved and learned a clever trick in our evolutionary past in order to find the time to feed our neuron-packed brains: we began to cook our food. By so doing, more energy could be extracted from the same quantity of plant stuffs or meat than from eating them raw.What solved the energy problem? Cooking. So, human brain size to mass ratio is normal but the energy the brain uses is off the charts. Cooking then, becomes part of the great leap forward.
The review (and the book) sound interesting. For the minimalistically inclined the last paragraph is particularly useful. It seems that the idea that language emerged very recently is part of the common physical anthro world view. Here's the SM's prose:
If a new neuronal scaling rule gave us the primate advantage at 65 million years ago, and learning to cook provided the human advantage at 1.5 million years ago, what, one might ask, gave us the “Homo sapiens advantage” sometime around 70,000 years ago? That was when our ancestors dispersed from Africa, to ultimately replace all other humans and reach the farthest corners and most extreme environments of the earth. It wasn’t brain size, because the Neanderthals’ matched Homo sapiens. My guess is that it may have been another invention: perhaps symbolic art that could extend the power of those 86 billion neurons or maybe new forms of connectivity that provided the capacity for language.So 75kya something happened that gave humans a way of using their new big energy consuming brains another leg up. This adventitious change was momentous. What was it? Who knows. The aim of the Minimalist Program is to abstractly characterize what this could have been. It had to be small given the short time span. This line of reasoning seems to be less and less controversial. Of course what the right characterization of the change is at any level of abstraction is still unclear. But it's nice to know the problem is well posed.
Here's a "humorous" piece by Rolf Zwaan by way of Andrew Gelman. It's a sure fire recipe for getting things into the top journals. It focuses on results in "social priming" but I bet clever types can make the required adaptations for their particular areas of interest. My only amendment would be regarding the garnish in point 2. I believe that Greek Philosophers really are best.
Have a nice Thanksgiving (if you are in the USA). I will be off for at least a week until the turkey festivities end.
Herculano-Houzel's current book really is worth reading, especially for the minimalistically inclined. A quite similar argument to has recently been made in the magazine section of Current Biology (a quick yet interesting read).ReplyDelete
I'll make an idle suggestion as to what the crucial thing might have been: an unlimited interface to memory. Which can lean more on discourse mechanisms (Piraha), or on complex sentence structure (Greek), but can in either case make use of an unlimited about of material that is not in the immediate environment.ReplyDelete