2009 January 26 Monday
The 10,000 Year Explosion: How Civilization Accelerated Human Evolution

Over the Christmas holidays I read a now just released and thoroughly enjoyable book by Gregory Cochran and Henry Harpending, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. I'll be writing a review about it shortly. Michael Blowhard is running a week-long interview with Greg and you can read the first installment. The core argument: we now have enough genetic sequencing data to know that the rate of human evolution has accelerated by a couple of orders of magnitude in the last 10,000 years. Says Greg:

2B: What genuine reasons were there ever to believe that human evolution stopped?

GC: I can't think of any genuine reasons for thinking that human evolution had stopped. Some people seem to have thought that 40,000 years was small potatoes compared to the time since the chimp-human split (five or six million years), so that there wouldn't have been much change over that time period. Of course this ignores the massive ecological changes that humans experienced over the last 40 millennia, and the resulting selective pressures.

Others seem to have thought that newly clever humans instantly came up with a technological fix for any problem that arose, which would have removed the selective pressure associated with the problem. Face it, we're not that smart. People suffered from malaria for thousands of years before figuring out that it was transmitted by mosquitoes (in 1897, by Ronald Ross) -- and we haven't knocked it out yet.

And often when we did solve problems, they didn't stay solved. For example, whenever we came up with better methods of food production, population increased until people were hungry again. At that point you see selection for metabolic efficiency, for the ability to digest newly available foods such as milk, etc.

I've run into this misunderstanding in a recent correspondence. My correspondent figured that we must not have been under much selective pressure because for the last few thousand years the human population was growing rapidly. Yet Europe was repeatedly hit by famines and disease outbreaks. Ditto for other parts of the world. Human populations expanded quickly in response to new ways to farm and then hit limits. We didn't break free of the food limits until the 19th century in some parts of the West and much later in some other parts of the world. Death by starvation still occurs today. One dig of medieval bones in Stockholm found that average adult life expectancy was less than 50 years. Those causes of death were selective pressures.

Death from war occurred too. While the term genocide gets batted around today for fairly small scale killings in the past invaders wiped out entire cities and regions. These killings were selective pressures on human evolution. We have not escaped selective pressures. Our human-caused environmental changes cause differences in who reproduces and how much.

Share |      By Randall Parker at 2009 January 26 11:48 PM  Human Nature


Comments
Bob Badour said at January 28, 2009 11:02 AM:

I was thinking about life expectancy the other day. I had severely impacted wisdom teeth as a teenager, and a root canal when I was college age. When one stops and thinks about it, anyone who has had an upper jaw root canal for an abscess might have died shortly after that age in previous times if the abscess made its way to the brain.

I might have died in my early 20's without a root canal and antibiotics.

I had a sinus infection a couple months ago that required intravenous antibiotics due its the proximity to my brain. If the infection in my 20's hadn't killed me, that one almost certainly would have taken me out at 43.

Stephen said at January 28, 2009 3:02 PM:

I was thinking along the same lines Bob (I had an inflamed appendix when I was 8) - in the modern world what does 'natural' mean in 'natural selection'?

I suppose the answer is that it means exactly what it has always meant - natural selection doesn't select with a conscious purpose or direction, it just selects for the currently existing environment.

In terms of those medical interventions, I guess that we're benefiting from inheriting genes that allow people to function in complex societies - eg higher cooperation, diminished agression, higher intelligence etc. People with those attributes are more likely to be able to sustain the kind of complex society that allows complex medical intervention and thereby live to procreate and so on. On the same point, having dodgy teeth & sinus genes isn't a selection factor in a complex society, but it would certainly be a big selection factor in other environments.

Bob Badour said at January 29, 2009 2:51 PM:

I wasn't objecting to the natural part of natural selection. I was only amplifying the point that we have undergone selective pressures in recent times. Randall's link about the average lifespan not so long ago being less than 50 reminded me of those thoughts. If I had been born even 40 or 50 years sooner, my risk of early death would have been much greater.

I have had three significant infections requiring antibiotic treatment (not just prophylaxis) and I am only 43. A couple generations before me, people raised lots of kids and conceived lots more who didn't survive long. Prior to antibiotics, relatively minor injuries often ended up in death or amputation. Contraceptives just introduce a new, huge selective pressure. Human evolution is far from over.


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