Why humans have no fur: Bare skin --> Bigger brains (Scientific American)

[brandon]

Our Brains Are Shrinking. Are We Getting Dumber?

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.

But not all researchers are so pessimistic. Brian Hare, an anthropologist at the Duke University Institute for Brain Sciences, thinks the decrease in brain size is actually an evolutionary advantage.

I'm not convinced on either of those theories. I think that Cro-Magnon man may have needed extra insulation in the skull to keep the brain warm in cold climates.

[Daft]

The link I've posted is no longer available :/

[brandon]

Our Brains Are Shrinking. Are We Getting Dumber?

I suppose if we lost our fur so our brains could get bigger without overheating, and then we started wearing clothes and our brains started shrinking, maybe wearing clothes is why smaller brains were once again favored. If we went naked again, we could support larger brains without our brains overheating.

[NakedKiwi]

What a fascinting article. I still wpnder what the tufts of hair we have about the place are for though.

[brandon]

What a fascinating article. I still wonder what the tufts of hair we have about the place are for though.

Hair on the head reduces the risk of skin cancer on the scalp and shoulders, the parts of the body most exposed to the mid-day sun in equatorial zones.

Armpit and pubic hair accumulate pheromones (excreted body chemicals) to stimulate sexual interest and reproduction.

Sexual selection is probably also a factor.

[prodigal_son]

I apologise if I'm repeating anyone here. Here's a couple more facts for the mix. Our brains only weigh 2% of our body mass but they use a staggering 20% of our energy.

The way we used to hunt was unlike anything any other animals did at the time. We don't have sharp claws or strong jaws to attack with. The way we hunted was to literally chase an animal until it collapsed from exhaustion. Animals lungs work like bellows, as they run their back legs come forwards and compress the internal organs blowing air out and as they stride out air gets sucked in. Think of a gazelle with its back legs nearly touching its front ones and then them taking a big leap. This controls their breathing, one breath to one step. However because we are upright on two legs our breathing can be at whatever rate we choose. And to lose heat most animals need to pant, and they do this by resting. But we can shed heat on the move by sweating. These hunts could take up to three-five hours before the animals got too exhausted. This is called persistence hunting.

Interestingly, what else takes 3-5 hours today? That's the average time for somebody to run a marathon. And what motivates us to go on such a long group run? The innate pleasure of a hunt is still with us.

[NakedKiwi]

Very insightful, thanks PS.

[Karla]

It really depends upon what that extra 10% of the brain actually did.

People generally think of intelligence as being able to play chess, do maths, solve problems etc. But you also need brain power for remembering things, for processing sensory stimuli and for moving. In fact the majority of our brain power is required for these things that we take for granted. There is less need for people to recognise smells nowadays for example. I personally define intelligence as the ability to adapt to an unknown environment. An excellent sense of smell would have limited value to your average person in the street. A hunter gatherer would probably have more use of it.

A bigger brain carries the cost of more risk from childbirth. Cesarian births have reduced this cost to some degree in relatively modern times though. I do sometimes wonder at how little need there is to learn and adapt in the average daily life once people have grown up and are settled into a job. I don't know for example whether we would need to make use of our short term memory as much as a hunter gatherer who would have to learn the way of the land and which berries to eat or not eat. But for each skills required of a hunter-gatherer you can point to another one of a modern day person that has developed since then.

More brain matter may be required for some neural processes than others. A large proportion of our brain is devoted to processing our visual senses for example.

[Bobbert]

I do sometimes wonder at how little need there is to learn and adapt in the average daily life once people have grown up and are settled into a job. I don't know for example whether we would need to make use of our short term memory as much as a hunter gatherer who would have to learn the way of the land and which berries to eat or not eat. But for each skills required of a hunter-gatherer you can point to another one of a modern day person that has developed since then.

I'd bet that the key to not getting to "settled" is to engage several different types of activities throughout the week or month.  You've got work and home life, but try dancing lessons or hiking or kayaking  or even reading to add some variety and put you in different circumstances and locations.

[Dan]

I don't know if large breasts have a biological advantage or if they are mainly the result of sexual selection.

Either, it's the same thing.

And yes, there was an advantage which I nearly completely forgot but it's about hiding the time of conception.

[Dan]

By the way, a big brain is not the ultimate weapon. Our ancestors won against Neanderthals which had bigger brains (unlike what cartoons led you to believe). Our competitive advantage was to evolve a jaw shape that enabled speech.

[Karla]

I do sometimes wonder at how little need there is to learn and adapt in the average daily life once people have grown up and are settled into a job. I don't know for example whether we would need to make use of our short term memory as much as a hunter gatherer who would have to learn the way of the land and which berries to eat or not eat. But for each skills required of a hunter-gatherer you can point to another one of a modern day person that has developed since then.

I'd bet that the key to not getting to "settled" is to engage several different types of activities throughout the week or month.  You've got work and home life, but try dancing lessons or hiking or kayaking  or even reading to add some variety and put you in different circumstances and locations.

That's my opinion too. I'm always trying to find completely different skills to learn.

[manwithaplan]

This is completely fascinating.  I love when science makes sense.  I don't understand why some people feel so threatened by science.  Oh yeah - religion.  I feel like people who are insecure in their religion attack science the most, just like men who are insecure in their masculinity attach homosexuality the most. 

[brandon]

An outstanding book I read recently that is somewhat related to the discussions here is:

Life ascending : The ten great inventions of evolution
by Nick Lane.

This book won the Royal Society prize for science books in 2010.

[skifan08]

I love this thread! To add to a couple of the very insightful things brandon said:

In addition to holding and helping in vaporization of pheromones, pubic and axillary hair also serves to reduce friction between damp sweaty skin and also create a gap between damp skin surfaces to aid in evaporation of sweat - this helps reduce the risk of fungal infections which otherwise love confined, non-ventilated spaces. (so, ironically, even though people say they shave their pits and pubes for "hygienic reasons" they are actually increasing their risks of developing fungal infections!)

Also, with the visible penis = sexual selection for longer penises idea - this has been used to explain why some of the longest flaccid penises (and foreskins) are seen in certain tribes in East Africa such as the Turkana people because they, even today, spend their lives naked. As a result women can very easily select for men with longer penises. The reason their foreskins are long is also interesting, as they view a male as only being truly naked when the glans is visible and so women select for men who best avoid the "embarrassment of being naked" by selecting men with longer foreskins...