Natural Selection Today

When Darwin first conceived of natural selection, he thought of it in terms of differential survival. Hence, the phrase "survival of the fittest." Modern biology, however, has moved away from Darwin's thinking on that point. Instead, biologists now talk about "reproduction of the fittest." It makes sense to focus on reproduction instead of survival, because simply surviving will not ensure natural selection, whereas successful reproduction will. In some cases, survival and reproduction are highly correlated, and that is probably how Darwin developed his thinking. But, reproduction, not simple survival, is the key to natural selection.

For example, think of species that reproduce and then die. Salmon and male tarantulas are two good examples. Even though they die shortly after reproducing, they have fulfilled the constraints of natural selection by doing so; their genetic line continues. Other good examples are genetic diseases that manifest themselves after the reproductive period of life. Those diseases persist in the species even though they may be quite lethal. However, their lethality occurs after reproduction. Contrast that to genetic diseases that have their effect in childhood. Those are much rarer because those affected rarely reproduce.

Finally, students may argue that evolutionists cannot agree with each other; therefore the theory itself must be faulty or wrong. Those disagreements are not usually about concepts like natural selection. Rather, the disagreements are about details. Most modern evolutionists agree as to the central core concepts of evolution like natural selection, fitness, and evolutionary history. They disagree over issues like punctuated equilibria versus gradual evolution, or about mechanisms of speciation. Today, evolution is a core concept accepted by most biologists, and it gives biology a useful way of interpreting its data.

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