WHAT ARE SOME EMPIRICAL EXAMPLES OF THESE CONDITIONS FOR NATURAL SELECTION?
Differences in rates of survival and reproduction are the driving force behind natural selection, and they usually vary greatly among organisms in the natural world. The Atlantic cod (Gadus morhua) is a dramatic illustration of this. The average female cod produces 2 million eggs in a single spawning, which would clearly lead to billions of cod very quickly if each and every one survived. However, 99% of these eggs die in their first month, and 90% of those remaining after the first month will die before their first year. This means that only about 200 of the original 2 million cod survive to age one, and by the time the cod get to their reproductive age of 2-4 years on average only 2 of the original 2 million are still alive. It is quite clear that those two cod would have their genes represented disproportionately in the next generation, and therefore any heritable traits that allowed those two fish to survive and reproduce would have strong selective pressure. Large mammals in the w
