I lay eggs to populate my species. Typically, there are 400-500 eggs in an average clownfish clutch, but 99% of baby fish will die before they hatch.
Step 2: Genetic Variation
This is my husband, Bob. He is a black clownfish. Since he is darkly colored, he is more likely to survive in the deep dark sea. That's why our kids are most likely to take on his coloring, so they're more likely to survive.
Step 3: Selection
Our kids are more likely to survive and give us grand-kids if they get my scale color. That's why most of our grand-kids will probably end up having my scale color.
Step 4: Adaptation
Over time, my family has gotten bigger fins. My grandmother had small fins, but we've adapted to our environment, and our fins grew to make us faster.
Our kids are more likely to survive if they have your skin, and my fins. If our kids are born with my skin, they'll have a harder time living and reproducing.