Vocabulary

ethologist behavior innate behavior fixed action pattern learning habituation operant conditioning classical conditioning reasoning imprinting sensitive period figure 44-1

"Hygienic" bees carry diseased or dead young from the hive. Studies have shown that this behavior is highly heritable.

"Hygienic" bees carry diseased or dead young from the hive. Studies have shown that this behavior is highly heritable.

figure 44-2

A male lion who has taken over a pride will often kill cubs fathered by rival males.

figure 44-2

A male lion who has taken over a pride will often kill cubs fathered by rival males.

Natural Selection and Behavior

Ethologists have hypothesized that animals usually behave in ways that promote their survival and offspring production. Because genes control some behaviors, natural selection can affect genetic variation that involves behavioral genes. Lions present a good example of this principle. The males living in a particular pride (family group) father all of the cubs. Eventually new males come along and force out the previous males. After the new males take over, they often kill cubs fathered by the previous males, as shown in Figure 44-2.

Observing this, ethologists wondered how natural selection could favor killing young of the same species? Further observation revealed that females will not breed with males as long as those females are caring for young. If the infants die, however, the female will mate again. By killing the existing offspring, the new male is likely to produce more offspring than males who do not kill cubs. Ethologists hypothesize that natural selection has favored genes that cause male lions to kill cubs that are not their offspring. It is important to remember that this behavior is instinctive. It is neither conscious nor deliberately aimed at other males or their offspring.

figure 44-3

This Eastern hognose snake (Heterodon platyrhinos) is "playing dead." The snake spreads its jaw, hisses, and rolls on its back.

figure 44-3

This Eastern hognose snake (Heterodon platyrhinos) is "playing dead." The snake spreads its jaw, hisses, and rolls on its back.

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