Why Humans Are Getting Dumber: Our Brains Are Shrinking!

Got a crotchety old guy who kept telling you that youngsters today are getting dumber by the minute (right before he told you to get off his lawn)?

Well, he may be onto something: scientists discovered that our brains are actually shrinking!

The downsizing of human brains is an evolutionary fact that took science writer Kathleen McAuliffe by surprise.

"I said, 'What? I thought it was getting bigger!'" she tells NPR's Jacki Lyden. That was the story up to 20,000 years ago, she learned. Then, the brains of our ancestors reversed course and started getting smaller — and they've been shrinking ever since.

Cro-Magnon man, who lived in Europe 20,000 to 30,000 years ago, had the biggest brains of any human species. In comparison, today's human brain is about 10 percent smaller. It's a chunk of brain matter "roughly equivalent to a tennis ball in size," McAuliffe says.

The experts aren't sure about the implications of this evolutionary trend. Some think it might be a dumbing-down process. One cognitive scientist, David Geary, argues that as human society grows increasingly complex, individuals don't need to be as intelligent in order to survive and reproduce.

I don't know about the science, but it sure explains Jersey Shore! http://www.npr.org/2011/01/02/132591244/our-brains-are-shrinking-are-we-getting-dumber

Photo: Emergency Inflatable Brain from the NeatoShop

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"brain shrinkage is correlated with agricultural development." - cwcaton.

I would be curious to know whether the pattern of shrinkage coincided with the development of agriculture as that may play into either or both of our hypotheses.
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If we are to suppose that brain size is correlated with intelligence, then we should be forced to conclude that men are smarter than women, on average.

Furthermore, we would be forced to conclude that Neanderthals were smarter than homo sapiens. Again, a hypothesis that is generally unsupported by the available evidence.

Here's an alternative hypothesis: brain shrinkage is correlated with agricultural development. Maybe our diets have changed to allow for smaller, more efficient brains. After all, there is certainly evolutionary pressure to have smaller, more efficient organs that consume less energy to perform th same tasks.
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Here's my uneducated theory: our brains might be smaller now because the extra brains we were carrying around were devoted to our sense of smell as that sense would be highly valuable in locating food sources both animal and vegetable in our hunter/gathere past. As we learned how to domesticate animals and grow our own food, a highly developed sense of smell was less necessary and the attending brain matter lessened over the generations.
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@Krikkit - the idea is brain size relative to body size. Our brains are (relatively) bigger than elephants' brains. Don't ask me why relative brain/body size is supposed to be important - it's just how the story goes.
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