Thursday, August 8, 2013

The Evolution Of Monogamy

Animal Behaviour

Chimpanzees are highly social primates, as shown by the three from the Miami Zoo. One view
on why monogamy evolved the way it did was that females were not highly available for the
purposes of mating, Balter of Science Mag says: “In contrast to Opie’s conclusion in primates,
they find in this larger sample that social monogamy arose among species where females were 
widely spaced and males could not monopolize several of them at once.”
Photo Credit: Matthew Hoelscher, 2007
Source: Wikipedia

An article, by Michael Balter, in ScienceMag looks at three possible theories on why monogamy evolved in animals, including primates, a species to which humans belong.

Balter writes:
Living in pairs, what researchers call social monogamy, has repeatedly evolved among animals, although in widely varying proportions among different groups. Thus, about 90% of bird species are socially monogamous, probably because incubating eggs and feeding hatchlings is a full-time job that requires both parents. But in mammals, females carry the babies inside their bodies and are solely responsible for providing milk to young infants—and only about 5% of species are socially monogamous. That leaves most mammalian males free to run around and impregnate other females. Primates, however, seem to be a special case: About 27% of primate species are socially monogamous; and recent studies by Christopher Opie, an anthropologist at University College London, and his colleagues have concluded that social monogamy arose relatively late in primate evolution, only about 16 million years ago. (The earliest primates date back to about 55 million years.)
But why did social monogamy arise at all among mammals, including primates, given the many reproductive advantages to males having access to as many females as possible? Scientists have proposed three major hypotheses: Monogamy provides more effective parental care for infants, as in birds; it prevents females from mating with rival males, especially in species where females are widely spaced and cannot all be easily monopolized by one male; or it protects against the risk of infanticide, which is very high among some primate species, including chimpanzees and gorillas, and is often explained by the desire of a rival male to quickly return a mother to a fertile state so that he can sire his own offspring. Some researchers think that a combination of all three factors, and perhaps still others, provide the best explanation for monogamy.
Resolving this debate is important, researchers say, especially for understanding the evolution of human mating behavior. Although humans aren’t completely monogamous, “the emergence of pair-bonding in humans was a major evolutionary transition, which dramatically altered the evolutionary trajectory of our species,” says Sergey Gavrilets, an evolutionary biologist at the University of Tennessee, Knoxville. Many researchers think that we could not have evolved our large brains without joint parental care during the extended period of helplessness required for infant brains to grow to their full size. “Understanding the forces that drove that transition can help us better understand the causes of human uniqueness,” Gavrilets adds.
Monogamy and parental investment are both good for society, and greatly explains why this model of human behaviour has lasted for millions of years. That the higher species with larger brains are more monogamous than the lower species makes perfect sense, in that it takes some higher-level thought process to understand the benefits of social pairing, notably when it comes to raising children.

How much primates understand is hard to know, since they don’t communicate with us in highly recognizable speech, and even the hand signs are limited in scope and the transfer of information, including emotion and feeling. We, for now, can only know what we observe, collate and interpret, forming ideas and conclusions from such observations. It is interesting to observe that humans are not the only mammals that pair off and raise children, showing our kinship to other mammals, notably to primates.

You can read the rest of the article at [ScienceMag]