Natural Selection Today

Modified: 2020-06-08

Charles Darwin crystallized earlier views of evolution in 1859 with his book The Origin of Species. Soon, his theory of evolution revolutionized biology and later psychology. Darwin never proposed a mechanism for evolution. At around the same time the Austrian monk, Gregor Mendel, discovered the science of genetics, another topic in this chapter. In the early 20th century biologists linked evolution and genetics into the "Modern Synthesis" of biology. Early psychologists, especially the Functionalist and later the Behaviorists linked their psychological theories to evolution as well.

Modern psychologists realize that all animals, including humans, are the product of a long evolutionary history. That "natural history" is one aspect of evolution that we'll see in this chapter when we discuss the evolution of the brain. The mechanisms of evolution will be covered somewhat when we discuss genetics. All humans share 50% of their genes from each parent. In the longer term, (think thousands of years) all species are subject to natural selection.

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.

Richard Dawkins' book, The Selfish Gene, argued that passing genes on to the next generation is the key to species continuity. Any living thing, he stated, could be looked at as a temporary container of genes. Sociobiology makes essentially the same argument.

Buss' research (video) on human jealousy is a good example of how evolution alters behavior. Men are much more jealous of their female partners sexual behavior where women are much more jealous of their male partners emotional behavior. Why? Buss points to reproductive differences. Men wish to ensure that their genes pass on to the next generation. Thus, men have evolved mechanisms (courtship, for instance) to be sure that their female partner is not already pregnant by some other man. Women, on the other hand, know that half of the genes of the baby she is carrying are hers. But, given the 18 years that will follow the pregnancy, women want a partner who will be around for the long haul.

Scarily, most women who are injured or even killed by their male partners are victims of sexual jealousy. Women, however, resent emotional jealousy more than sexual jealousy. Imagine the following statement made by a male partner: "I can talk to your friend Mary about anything, she understands me better than you every will." That statement will arouse much emotional jealousy!

Now imagine the female partner saying: "I can talk to your friend Tom about anything. He understands me better than you." The male partner's reply might be, "Are you sleeping with him?" If she say no, he will probably be fine. Can you see the difference in the two types of jealously now?

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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