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I'm writing a scene where one of the characters is explaining the process of natural selection:

“Think of it as a beach full of crab holes of various shapes and sizes, and with little pebbles on the upper part, sculpted over hundreds and hundreds of years by crashing waves. The pebbles are constantly being dragged down by the waves and occasionally fall inside the crab holes. These 'selected' pebbles aren't necessarily smoother or more symmetrical. On the contrary, they could be the most deformed of the bunch, it's just that they had the right shape for a certain hole.

Is the analogy above effective and clear?

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Close. Part of the process of evolution is that it doesn't happen once, but repeatedly over a long period of time, and that "falling through a particular hole" allows something beneficial to happen later on (reproduction and thereby continuance of the species).

If the pebble doesn't fall through the hole, you have to explain what bad thing would happen. And once the pebble is through the hole, something else needs to occur so that the cycle can repeat, and the next pebble is better-suited to do the next thing, whatever it is.

What you've described is the beginning of natural selection, but you haven't completed the analogy.

  • Oh, you're right. But the character just wants to point out are not the perfect pebbles that fall down but those with right shapes. So maybe I don't have to explain the whole process? – Alexandro Chen Oct 10 '14 at 10:16
  • @AlexandroChen Your metaphor is fine if that's what the character is trying to express. But then that's not what you posted about. Which is fine; it just means that you didn't post what you actually wanted to ask. The character is describing the process of natural selection, which is one part of Darwinian evolution, not all of it. – Lauren-Reinstate-Monica-Ipsum Oct 10 '14 at 12:10
  • I edited the question. How about now? – Alexandro Chen Oct 10 '14 at 12:12
  • @AlexandroChen Your analogy is more precise than your question (it's not about "good or bad" but about "what works in that situation"), so yes, you've got it. :) – Lauren-Reinstate-Monica-Ipsum Oct 10 '14 at 13:23
  • I guess I'm better at writing analogies than questions. – Alexandro Chen Oct 10 '14 at 13:38
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The problem with the analogy is that evolution is not just that certain shapes are more fit than others.

There must be iteration, so that the best of terrible fits is selected.

When I begin a genetic algorithm (a form of search for a solution to a problem using a computer), all the organisms are randomly generated, and not one of them is anywhere NEAR close to a good solution.

But they are designed so that, by the simple logic of a shot gun blast, some are marginally better than others. So I can find the best half of this completely useless lot.

The magic of evolution is mating randomly chosen members of the best half, to produce unique NEW members that replace the worst half, and then evaluating these and sorting the population again.

Any analogy of evolution is poor if it does not stress the crucial role of mating and mutation for improvement on some criterion (in real evolution this is success in mating, which can favor elements like offensive and defensive abilities for survival or competing for mates).

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