Coolidge effect
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In biology and psychology, the term Coolidge effect describes a phenomenon—seen in nearly every mammalian species in which it has been tested—whereby both males and females exhibit continuous high sexual performance given the introduction of new receptive partners.[1][2]
Contents [hide]
1 Origin of the term
2 Empirical evidence
3 On simultaneous hermaphrodites
4 See also
5 References
[edit]Origin of the term
The term comes from an old joke, according to which U.S. President Calvin Coolidge and his wife allegedly visited a poultry farm. During the tour, Mrs. Coolidge inquired of the farmer how his farm managed to produce so many fertile eggs with such a small number of roosters. The farmer proudly explained that his roosters performed their duty dozens of times each day.
"Tell that to Mr. Coolidge," pointedly replied the First Lady.
The President, overhearing the remark, asked the farmer, "Does each rooster service the same hen each time?"
"No," replied the farmer, "there are many hens for each rooster."
"Tell that to Mrs. Coolidge," replied the President.
[edit]Empirical evidence
The original experiments with rats followed this protocol:[3] A male rat would be placed into an enclosed large box with four or five female rats in estrus. He would immediately begin mating with all of the female rats repeatedly until eventually exhausted. Although the females would continue nudging and licking him to continue, he would not respond. However, if a novel female were introduced to the box, he would become alert and find the ability to mate once again with the new female. This phenomenon is not limited to Rattus norvegicus.[4] It is attributed to an increase in dopamine levels and its subsequent effect upon the limbic system.[5]
Human males experience a post-ejaculatory refractory period after sex. They are incapable of engaging in sex with the same female after ejaculation and require time to recover full sexual function. In popular reference, the Coolidge effect is the well-documented phenomenon that the post-ejaculatory refractory period is reduced or eliminated if a separate female becomes available.[6] This effect is cited by evolutionary biologists as a reason why males are more likely to desire sex with a greater number and variety of partners than females.[6]
While the Coolidge effect is usually seen demonstrated by males—that is, males displaying renewed excitement with a novel female—Lester and Gorzalka developed a model to determine whether or not the Coolidge effect also occurs in females. Their experiment, which used hamsters instead of rats, found that it does occur in lesser degrees in females.[7][8]
[edit]On simultaneous hermaphrodites
A 2007 study focusing on the Coolidge effect in simultaneously hermaphroditic species confirmed the validity of the Coolidge effect in freshwater snail Lymnaea stagnalis.[9] Biomphalaria glabrata, another simultaneous hermaphrodite freshwater snail, does not exhibit sex-specific effects of partner novelty, and thus there is no Coolidge effect in the species.[10]
