1-03 The Genetics Of Behavior (Part 2)

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Objective

Describe four misconceptions about evolution.

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1. Does the use or disuse of some structure or behavior cause an evolutionary increase or decrease in that feature? This misconception arises from Lamarck’s theory of evolution, which postulates that an individual can inherit acquired characteristics to their offspring. According to the idea, if giraffes stretch their necks as far out as possible, their offspring will have longer necks. Similarly, if you exercise your arm muscles, your children will be born with bigger arm muscles. However, biologists have found no mechanisms for Lamarckian evolution to occur or evidence that it does.

2. Have humans stopped evolving? Because of the effectiveness of modern medicine in keep humans alive and because welfare programs in prosperous countries provide the necessities of life for almost everyone, many assert that humans are no longer subject to the principle of “survival of the fittest”. Thus, they claim that human evolution has slowed or stopped. The flaw in this argument is that the key to evolution is not survival but reproduction. For someone to spread their genes, they need to survive long enough to reproduce (of course), but what matters is how many healthy offspring they produce. Thus, keeping people alive does not stop human evolution.

3. Does “evolution” mean “improvement”? It depends on what you mean by “improvement”. Yes, evolution improves the average fitness of the population, which is defined as the number of copies of one’s genes that endure in later generations. Thus, if you have more children than average, you are considered evolutionarily fit, regardless of success in other life domains. Any gene that spreads is by definition fit. However, genes that increase fitness at one time and place can become disadvantageous after an environmental change. For example, the colorful tail feathers of a male peacock enable it to attract females but might also become disadvantageous in the presence of a new predator. In other words, genes of the current generation evolved because they were fit for previous generations; they may or may not be adaptive in the future.

4. Does evolution act to benefit the individual or the species? Neither: It benefits the genes. Genes use you to reproduce themselves. A gene spreads through the population if the individuals bearing that gene reproduce more than other individuals do. For example, imagine a gene that causes you to risk your life to protect your children. That gene will spread through the population, even though it endangers you personally, provided that it enables you to leave behind more surviving children than you would otherwise.

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Objective

Name at least two plausible ways for altruistic genes to spread in a population.

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1. Reciprocal altruism—the idea that animals help those who help them in return. Two individuals who cooperate with each other will prosper; however, reciprocal altruism requires that individuals recognize one another and learn to help only those who return the favors.

2. Kin selection—selection for a gene that benefits the individual’s relatives. For example, a gene could spread it if it caused you to risk your life to protect your children, who share many of your genes, including perhaps the altruism genes. Natural selection can favor altruism toward less close relatives—cousins, nephews, etc.—if the benefit to them outweighs the cost to you.

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evolution

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Change over generations in the frequencies of various genes in a population

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artificial selection

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The process by which plants and animal breeders choose individuals with a desired trait and make them the parents of the next generation

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Lamarckian evolution

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Idea that an individual can inherit acquired characteristics to their offspring

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fitness

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Number of copies of one’s genes that endure in later generations

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evolutionary psychology

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Branch of psychology that deals with how behaviors have evolved, especially social behaviors

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altruistic behavior

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An action that benefits someone other than the actor

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reciprocal altruism

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The idea that animals help those who help them in return

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kin selection

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Selection for a gene because it benefits the individual’s relatives