Saturday, September 28, 2013

Why are there so few people over 115 years of age?

A correspondent writes in about Matt Ridley's blog post "Why are there so few people over 115 years of age?" which doesn't actually answer that question,

The human body is a tightly-coupled network with several vital nodes: brain, heart, lungs, liver, pancreas, gut, kidneys, and so on. It has limited redundancy: two lungs and two kidneys. Degradation in one organ indicates degradation in other organs. Past degradation in an organ quickens the pace of future degradation in that organ and in other organs. There is self-repair, but it is limited by the lack of biological usefulness of extremely old people. There is no evolutionary pressure to extend the life of anyone too old to help a mother tend her babies. Given a particular design, the Second Law of Thermodynamics assures that there will be some overall limit to life span. If we were embodied by silicon chips, it would be longer.

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