A NEW KIND OF SOCIAL SCIENCE FOR THE 21st CENTURY
A Conversation with Nicholas A. Christakis [8.21.12]
"Let me just set the stage with a couple of examples. Since we evolved from our hominid ancestors, it took about 300,000 years to double our life expectancy, till it was approximately 40 years of age. In other words, about 300,000 years ago, we had a life expectancy roughly speaking of about 20 years. About 200 years ago, we had a life expectancy of about 40 years. But in the last 200 years, we've doubled it again. It was a change that took 300,000 years in the first instance, which might have been almost imperceptible. If you had asked me a thousand years ago, "Is human life expectancy changing?" I might have said no. So, a change that took 300,000 years to occur in the first instance, in the second instance, takes 200 years. Life expectancy is indeed increasing dramatically, at least over this interval of time.
Another example of this tension between whether things are changing or not changing is the debate about whether or not human beings can evolve in historical time, under the pressure of historical forces. I used to think that this was not possible. But there's been a huge amount of work by many labs around the country in the last 10 years or so documenting that we humans are evolving in real time. The famous, best example of this is the evolution of lactase persistence into adulthood. The ability to digest lactose, which is a sugar in milk, isn't really of any value in adulthood until you have a stable source of milk. It turns out that human beings have independently evolved this capacity to digest milk as adults a half-dozen times, in different settings around the world, coincident with the cultural innovation of domesticating animals—domesticating sheep, goats, or cows, which provides a ready supply of milk. This milk is a good food source in times of scarcity. It's also a good source of unspoiled hydration. So this confers survival advantages."
Another example of this tension between whether things are changing or not changing is the debate about whether or not human beings can evolve in historical time, under the pressure of historical forces. I used to think that this was not possible. But there's been a huge amount of work by many labs around the country in the last 10 years or so documenting that we humans are evolving in real time. The famous, best example of this is the evolution of lactase persistence into adulthood. The ability to digest lactose, which is a sugar in milk, isn't really of any value in adulthood until you have a stable source of milk. It turns out that human beings have independently evolved this capacity to digest milk as adults a half-dozen times, in different settings around the world, coincident with the cultural innovation of domesticating animals—domesticating sheep, goats, or cows, which provides a ready supply of milk. This milk is a good food source in times of scarcity. It's also a good source of unspoiled hydration. So this confers survival advantages."
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