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WHY ANIMALS LINK UP
HUMANS AND some other mammals practice social monogamy; one guy, one gal, more or less for life. Researchers have done lots of work seeking clues about the evolutionary benefits of this. One view, typically posited for humans, is that a need for parental care leads to monogamy. This isn’t the only rationale, though. An article, “The Evolution of Social Monogamy in Mammals,” in Science, 2 August 2013, offers insights into this.
Researchers D. Lukas and T.H. Clutton-Brock at the Department of Biology, University of Cambridge, studied socioecological and life-history data of 2545 non-human mammalian species ranging from tiny shrews to whales. They identified 61 independent transitions of species to monogamy, all but one from ancestral species with solitary females.
The typical situation was solitary females mating with roaming males. Generally, a female was intolerant of her sisters, in fact, in actual competition with them. This precluded breeding males from any hope of guarding more than one female.
But he could defend one.
Lukas and Clutton-Brock observe, “Our results suggest that social monogamy evolved in mammals where feeding competition between females was intense, breeding females were intolerant of each other, and population densities were low. Under these conditions, guarding individual females may represent the most efficient breeding strategy for males.”
This hypothesis is corroborated in “Why Male Mammals are Monogamous,” in the same Science issue. Researcher Peter M. Kappeler, University of Göttingen, observes, “Thus, female mammals set the ground rules, and males map themselves onto their distribution…. When faced with solitary females, males have two options: They can either roam widely, trying to cover and defend the ranges of several females, or they can associate and settle with one female and form a pair.”
This is far from the norm among mammals. Plenty of modern species continue the solitary female/roaming male model (68 percent); squirrels, cheetahs and armadillos among them. Another model is singular cooperative breeding (23 percent), in which a dominant female’s offspring are reared by lesser females of the group; bats, wild goats and fur seals are examples of this.
Social monogamous mammals (9 percent) include elephants, beavers and New World owl monkeys. Monogamy varies among mammalian orders: primates 29 percent, carnivores 16 percent, but whales, dolphins and porpoises, none at all. By contrast, 90 percent of birds form monogamous pairs.
Evolutionary of mammals. Image from Science, 2 August 2013.
All African apes are polygynous, one male, several females, with group living. Hence, it’s likely that hominid ancestors were also polygynous. It has been suggested that the evolution of human monogamy arose from the need for extended parenting.
Lukas and Clutton-Brock offer a contrasting point of view, “… the shift to monogamy in humans may be instead the result of a change in dietary patterns that reduced female density and limited the potential for males to guard more than one female.”
That is, our monogamy may have followed the same evolutionary pattern of those 60 other mammals. ds
© Dennis Simanaitis, Simanaitis Says.com, 2013
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