The average female cod produces two million eggs in a single spawning; however, only about 200 of the original two million cod survive to age one. When cod reach their reproductive age of two to four years, only two of the original two million are still alive. What can you conclude about the traits of the two cod that survived?

The traits of the two cod that survived are advantageous, giving them a reproductive advantage. Also, these traits have strong selective (evolutionary) pressure. Selective pressure refers to any cause that tends to reduce reproductive success in a population. Traits that mitigate the effects of selective pressure can become widely spread through a population.