Evolution - How did different systems of organs come into being?

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2012-06-06 5:36 pm

I’ve just started reading some brief introduction to evolution on the web. It’s easier to understand evolution of individual organs due to mutation and natural selection. But how did different organs evolved in such a well structured and well coordinated way that it seems to be ‘built’ by someone instead?

Take the digestive system as an example: food gets in through the mouth, get processed and get out through a lengthy intestine. As it involves different parts of the body, it's hard to figure out how some organs evolved into being to fit others, especially those organs that 'know their way' and go around long length in the body, a system which seems to be ‘built’ by someone with a design in mind instead. I read from the web there is something like ‘information about the environment’, etc, and don’t know whether it’s relevant and if yes, how. As I didn’t study biology, would you explain it in an accessible way?

Note: I don't mean to start a debate between evolution and creationism. I just want to hear about how evolution works.

回答 (1)

[匿名]

2012-06-06 5:41 pm

✔ 最佳答案

The answer is very complex, but I'll give you the simple version: the neural tube.

When a clump of cells is forming into what will become a fetus, they form a tube. This gives rise a lot of structures, such as your spine. It also forms a tube that runs from your mouth to your rectum. Parts of that tube are wider, and parts are narrower. Parts of it are fairly straight, and parts of it fold up like a piece of string dropped onto the floor.

Look at a snake. It is pretty much a straight tube for digestion. As snakes evolved into lizards, the digestive system stayed fairly simple. Over time, more complex structures evolved, with some specialization. A lizard somewhere had a mutation that caused a bulge in the digestive tract. That lizard gave birth to other lizards with a similar bulge. Food accumulated in that bulge and was better digested, giving those lizards with a bulge an advantage over other lizards, so that mutation spread in the gene pool. You now have a gizzard. Later mutations gave rise to further specialization.

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