Wednesday, January 29, 2014

Natural Selection's Brain Building

 


Three Scoops Of Ice Cream
A lizard brain is about survival — it controls heart rate and breathing, and processes information from the eyes and ears and mouth.
When mammals like mice came along, the lizard brain didn't go away. It simply became the brain stem, which is perched on top of the spine, Linden says.
Then evolution slapped more brain on top of the brain stem.
"It's like adding scoops to an ice cream cone," Linden says. "So if you imagine the lizard brain as a single-scoop ice cream cone, the way you make a mouse brain out of a lizard brain isn't to throw the cone and the first scoop away and start over and make a banana split — rather, it's to put a second scoop on top of the first scoop."
That second scoop gave mammals more memory and a wider range of emotions. It also allows a mouse to do things a lizard can't, like using experiences to anticipate danger instead of just responding to it.
To create the brain found in apes, Sherwood says, evolution added a third scoop. It allows apes to reason and live much more complicated lives than mice.
"In these brains, you can find all of the very same parts that you would see in a human brain," Sherwood says. But there's a difference — the brain of an adult human is about three times the size of a gorilla brain.
 The human brain continues to grow rapidly for the first five years after birth. It takes 20 years before all the circuits are l
In one sense, we've had to pay a heavy cost for our big, inefficient brains: Childbirth is difficult, childhood is long, and our brains consume 20 percent of the calories we eat.
But Linden says these adaptations turn out to have some surprising payoffs, like romantic love.
"If our neurons weren't such lousy processors and we didn't need 100 billion of them massively interconnected in order to make a clever brain out of such lousy parts, then we wouldn't have such a long childhood," Linden says.
And without that long childhood, he says, evolution wouldn't have equipped us with the force that bonds parents together to protect their children.aid out and connected up, Linden says.

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