We live long:
So humans live longer than apes.  (Heather Pringle, Long Live the Humans SCIENTIFIC AMERICAN vol. 309 no. 4 October 2013 page 49) The logic of the article is that as our ancestors a couple of million years ago began to eat substantial quantities of meat they perforce developed immune systems that could cope with the new infectious risks this change entailed, and it is this new souped up immune system that is responsible for our longer lives.  Indeed it is not just modern medicine that keeps us alive long; even in its absence humans outlive chimpanzees.

Hmm.  My mind is full of crashing gears and smoking wires.  I can’t make sense of that.  For one thing I have long thought that I was told that chimpanzees have immune systems far superior to those of humans.  Their promiscuous social arrangements expose them to far more risk of infection than humans face from fishing a hunk of meat out of the fire. 

On top of that, well, everything has to be a trade off.  The body does not make the strongest immune system that the laws of nature could permit; it makes an immune system that balances the upside of defeating an infection with the – the article suggests – down side of producing things like vascular disease later in life.  It also balances the advantage of the immune system against the resources it takes to support it.

If something is in equilibrium and you push it north you can expect a response to push it south, but you would be quite surprised to have it wind up farther south than when you started. 

So I think the answer is not in on this yet. 

I suspect that it is part of a sort of overall advantage humans have.  We get everything.  Sure we have the big brain and the technology.  And we have dexterous hands.  Also human women are prettier than other female animals; again and again I have seen non human vertebrates go ga ga over a woman.  We hold our breath longer than some aquatic animals and dive deeper than many aquatic animals.  A porpoise has a single sphincter to defend its airway; we have a nose that can be pinched shut or stoppered with the upper lip or soft palate , a mouth that can be sealed at the lips, turned into a filter at the teeth, sealed at any or all of at least three levels by the tongue, and then the common airway can be sealed by the cords, the false cords or above. 

There is something out there that has permitted us to develop these things and many more.  I suspect it is our pattern of low fertility and high survival; fewer humans die simply by random chance than other animals.  We are so good at surviving that if we fail to survive there is a reason, and that reason will persist and thus become the target of efficient selection.

At least that’s what I think today.

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