Monday, 30 July 2012
The Shrinking Human Brain: What Does It Mean?
We all know that a few interesting hyperlinks and a bit of curiosity can add up to a massive waste of time. But sometimes it can be time well wasted. Consider, for example, what I learned on the little trip through cyberspace that I’m going to tell you about now.
Since I live in Montreal and write a web site about the human brain, the on-line article that I’ve listed as the first link below caught my eye. It’s from McGill University, in my home town, and it discusses a book called Big Brain, published in 2008 by two neuroscientists, Gary Lynch and Richard Granger. In this book, the authors describe the discovery of the “Boskops” skull in South Africa in the early 1900s. They say that this skull suggests the existence of ancient beings whose brains were more than 30% larger than the brains of humans today and who were therefore probably capable of more complex thinking than modern humans.
But as the article from McGill stated, many paleontologists doubt this book’s theory that Boskops represented a separate species of hominid. And when I clicked a link in this article, it took me to an excerpt from Big Brain published online in Discover magazine in 2009 (see 2nd link below), where the introduction stated that this theory is controversial and gave me a link to a very different view: a post that paleoanthropologist John Hawks made on his blog when the book first appeared in 2008 (see 3rd link below). In his post, Hawks stated that the Boskops have “not been a going topic in human evolution for nearly fifty years” and that the anthropological knowledge in question is obsolete. According to Hawks, the authors of Big Brain failed to consider recent archaeological data that paint a very different picture of Boskops.
As I saw on his blog, after Discover published the excerpt from Big Brain in 2009, Hawks updated his post about it (4th link below). This time, he focused his criticism on a few specific assertions in the book, including the possible existence of a human population with an average brain size of 1 750 cubic centimetres or with an “inconceivably large prefrontal cortex”, and the correlation between brain size and intelligence.
“Well,” I said to myself as I began to close all these windows in my browser, “if I want to illustrate a lively scientific controversy, I’ve got plenty of material here.” But then, down at the bottom of the article from Discover magazine, a link to another article that the magazine had published online later on, in 2011, caught my eye. It was a fantastic piece of investigative journalism by science reporter Kathleen McAuliffe. Its title read “If Modern Humans Are So Smart, Why Are Our Brains Shrinking?”
I couldn’t resist: I clicked on the link, and found that the story began with the account of an interview that McAuliffe had conducted with none other than John Hawks. While listing various changes that have affected the human brain in the course of evolution, he had dropped the following bombshell: “And it’s also clear the brain has been shrinking.”
Dumbfounded, McAuliffe cited all of the paleontological data showing that brain size had increased in the course of hominization. But Hawks explained, “That was true for 2 million years of our evolution. But there has been a reversal.” Recently (over the past 20 000 years or so), the average volume of the human male brain has decreased from 1 500 cc to 1 350 cc. This loss of a chunk of brain the size of a tennis ball is, in Hawks’s words, “a major downsizing in an evolutionary eyeblink.”
According to McAuliffe’s research, so far only a small circle of paleontologists seem to be aware of this strange phenomenon. But as she reports, they offer all kinds of theories to try to explain it. One of the most interesting is that since humans became more sedentary and began to live in larger groups, they have “domesticated” themselves. How so? Of the roughly 30 species of animals that human beings have domesticated, every one has lost 10 to 15% of its brain volume compared with its wild ancestors. Primatologist Richard Wrangham sees this as an evolutionary selection against aggression, favouring juvenile characteristics and hence a smaller brain.
It’s still hard to say whether the species thus domesticated, with their smaller brains—perhaps including ourselves—are more intelligent, or less. But one thing is certain: as a result of this evolutionary drift, their forms of intelligence are different. After drifting around the Internet from one of these links to the next, I feel safe in saying that much.
Neuro Science 101 – The Evolution of Big Brains
What Happened to the Hominids Who May Have Been Smarter Than Us?
Return of the “amazing” Boskops
If Modern Humans Are So Smart, Why Are Our Brains Shrinking?