dye

This may help.

Consider a group of insect in a forest.

Random mutation may causes some insect to have a skin color from infrared to ultraviolet.  

"突變是隨機的"

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But here comes along a bird that eat the insects.  If the ground is green at the moment and the insect is also green.  The insect with green skin will manage to hide (and populate).  

The insect poplation is said to evolve to have green skin.  You can throw in the pack of insect with different color to the same environment again, the green ones will always be the result.  

Change the environment to red and the red insect will always be the result.

It is totally unrandom.  It is dictated by the environment (which in turn is dictated by the law of physics)

自然選擇是你可以想像到的最不隨機的力量。

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Something simliar is happenin to human with milk.

Random mutation may causes some human to be lactose tolerant as an adult.  (Our ancestor are lactose intolerant at adult)

"突變是隨機的"

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As our society change, we created an environment where drinking milk is important as an adult (after domestication of cattles, milk become an important part of our  diet.  Anyone that cannot drink milk as an adult has one less important food source, and sits at a disadvantage)

Enventually, we have the society we have today where many of us is lactose tolerant.  

自然選擇是你可以想像到的最不隨機的力量。

But it can be reverse.  As in some society, milk consumption is still not a major part of the diet.  (Chinese, for example, are not fond of drinking milk, and has more lactose intolerant population)  Usually, nomadic orgin fellow are lactose tolerant, while farmer origin are lactose intolerant.

[ 本帖最後由 dye 於 2008-4-3 17:07 編輯 ]