02-13-08 - 1

Watching the Nature episode "Crash" about the Red Knot seabird that lost 90% of its population in almost one generation due to human disruption of their food source. It reminds me of something I wrote in "Fitness" about how the human anatomy has evolved to not build unnecessary muscle. You see with this occurance of the Red Knot how catastrophic events can cause massive rapid genetic selection. Up until the 1970's or so, everyone thought of genetics as gradually evolving over the aeons, lots of tiny changes adding up. We now know (and it seems quite obvious in hindsight) that in fact the overall genetic makeup of the population makes very rapid and massive changes in response to cataclysmic events. Lots of minor differences evolved into the population over the years, and they weren't strongly selected. Then suddenly something happens and every individual without a certain gene is dead, either from famine, or a disease, or a change in a food source or a predator. With humans, there have been countless famines (and a recent ice age and plague) which have wiped out the individuals that built muscle more easily and required more food to survive.

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