It’s the ultimate form of “Survivor,” the quintessential mano-a-mano struggle, but this show’s been going on for millions of years.

It is, of course, the human species’ fight for survival, against the elements, against the odds, and, most especially, against his fellow man. And, while it’s been a perilous journey, from those nascent moments Homo Sapien branched away from his primate cousins on the evolutionary tree, it’s tested our collective metal and quite literally expanded our brains.

In fact, researchers at the University of Missouri are convinced that the very day-to-day competition for survival has been the primary factor behind the tripling in size of the human brain over the millennia.

U-of-M Professor David Geary studied 153 hominid skulls, comparing them with human migration patterns and population density.

He found that that an area with a larger population led to more social competition, sort of a primitive “social ladder.”

According to Geary, “People are jockeying, manipulating and competing their way up that ladder.” And with higher access, species secure more food, mates and shelter and, ultimately, a better chance at survival. While those on the lower rungs become extinct and footnotes in the pages of history.

He contends that with growing social competition, specific parts of the brain—like the neocortex—have grown in size. The neocortex is vital to higher functions like sensory perception, motor commands, and conscious thought. All handy traits to have, if you're trying to catch dinner on the savannah, or are trying to avoid becoming it yourself.

And while the human brain has been evolving and growing in size for four million years, the biggest spurt coming in just the last 100,000 years. So, the competition has grown fiercer as the human species has continued to develop.

Geary believes that social competition has been more critical to human brain growth than other factors, such as climate change and ecological demands.

Of course, with all the dire predictions about global warming's threat to mankind and the planet, that may very well change over the coming decades.