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?