It's being argued that we were only able to evolve big brains because the cooling climate allowed us to burn off the excess heat created by bigger brains. Many people may not realize just how much energy is required by their brains: that bundle of neurons in your skull burns through nearly half of the energy you use while at rest. This generates a lot of excess heat (Remember mom telling you to wear your hat in the winter? You lose a lot of body heat through your head) that would cause more problems in a hot climate.
Bob Holmes writes in New Scientist (August 1, 2009):
Over the years, researchers have come up with three broad reasons why bigger brains might have been advantageous: to give their owners the ability to cope with changing climates by exploiting technologies such as shelter, fi re and clothing; todeal with the cognitive demands of hunting and gathering; or to help people outsmart their neighbours.
To help narrow this down, Geary collected data from 175 fossil hominin skulls, from 1.9 million to 10,000 years old. Then he looked to see whether brain size was best correlated with climatic variability - a crude measure of biodiversity which could indicate the complexity of hunting and gathering -or the human population size at the time, which could reflect the complexity of social interactions.
Geary's analysis found that population size was the best predictor of brain size, suggesting that our ancestors' need to outcompete their neighbours in order to survive may have been the strongest driver of brain growth (Human Nature, vol 20, p 67).
The case is far from closed -- Geary's study does not demonstrate cause and effect, for one thing -- but the picture beginning to emerge suggests that an ice age set the stage for a socially driven brain boom. And from that time on, it was the brainiacs who stole the show
David Schwartzman and George Middendorf of Howard University in Washington DC were the first to hypothesize that an ice age was needed for our big brains to develop, but that was a decade ago and they didn't have any hard evidence to support his idea. Now, though, there is supporting evidence -- it's not unambiguous by a long stretch, but it is good evidence for an explanation that makes a lot of intuitive sense.
Of course, this is all just a naturalistic explanation for a naturalistic development of hominid biology -- just what you'd expect from science. Notice how there is no need for or effort to use "God" as an explanation here for why humans have large brains. The presence of a naturalistic explanation doesn't just help eliminate the need for supernatural explanations from religion, but it also makes it harder to hold on to all the things that supernatural explanation is needed to support -- like souls, an afterlife, sin, etc.
If our big brains were a natural, evolutionary product of the natural environment and our genetic code, then where would a soul come into the picture? It's would be hard to argue that the presence of a soul dependent on a bigger brain, never mind a brain that evolved only because the climate made it possible. If, however, souls still weren't presence, then how and why would they appear at any later date -- if the brain isn't a relevant conditions, it's hard to see how anything else could be.
I think the big brain helped us to make up for our weak bodies. We became smart instead of strong. Other animals didn’t need a large brain to survive so didn’t develop one. What it means really is that random mutations working negatively might have counteracted brain growth in animals which could still survive. Hominids couldn’t. They needed a bigger brain. In fact all the hominids bar man became extinct.
Maybe a big brain isn’t so good. It goes along withh big wars and other conflicts. It encourages sociopaths.
I’m from Wisconsin. Damn near froze my *ss once, and I don’t think my brain got any bigger. So much for the ice age theory.
You sir are an idiot. That isn’t how evolution works at all. There are so many people who just don’t understand the concept and when it’s explained to them, refuse to think/accept it…it’s irrefutable!