8/22/13 - why sex?

In today's encore selection - is sex really necessary? After all, if the evolutionary goal of each individual is to get as many genes into the next generation as possible, wouldn't it have been simpler and easier for the early organisms to have just replicated or made clones? The likeliest explanation is that the genetic shuffling and resulting variation that occurs from sex-based reproduction keeps enough diversity in the species to minimize risk from bacteria, viruses and other parasites. And since we're on the subject, after sex, why does the male stay involved? From the stand point of biology, males have more or less nothing to do after copulation:

"Approximately two billion years ago a pair of single-celled organisms made a terrible mistake -- they had sex. We're still living with the consequences. Sexual reproduction is the preferred method for an overwhelming portion of the planet's species, and yet from the standpoint of evolution it leaves much to be desired. Finding and wooing a prospective mate takes time and energy that could be better spent directly on one's offspring. And having sex is not necessarily the best way for a species to attain Darwinian fitness. If the evolutionary goal of each individual is to get as many genes into the next generation as possible, it would be simpler and easier to just make a clone.

"The truth is, nobody really knows why people -- and other animals, plants and fungi-prefer sex to, say, budding. Stephen C. Stearns, an evolutionary biologist at Yale University, says scientists now actively discuss more than 40 different theories on why sex is so popular. Each has its shortcomings, but the current front-runner seems to be the Red Queen hypothesis. It gets its name from a race in Lewis Carroll's Through the Looking Glass. Just as Alice has to keep running to stay in the same place, organisms have to keep changing their genetic makeup to stay one step ahead of parasites. Sexual reproduction allows them to shuffle their genetic deck with each generation. That's not to say that sex is forever. When it comes to reproduction, evolution is a two-way street. When resources and mates are scarce, almost all types of animals have been known to revert to reproducing asexually. ...

"What persuaded the male hominid to stick around after mating? From the standpoint of biology, males have nothing to do after copulation. 'It's literally wham-bam thank-you-ma'am,' says Kermyt G. Anderson, an anthropologist at the University of Oklahoma-Norman and co-author of Fatherhood: Evolution and Human Paternal Behavior. What made the first father stick around afterward? He was needed. At some point in the six million years since the human lineage split from chimpanzees, babies got to be too expensive, in terms of care, for a single mother to raise. A chimp can feed itself at age four, but humans come out of the womb essentially premature and remain dependent on their parents for many years longer. Hunters in Amazonian tribes cannot survive on their own until age 18, according to anthropologist Hillard Kaplan of the University of New Mexico-Albuquerque. Their skills peak in their 30s -- not unlike income profiles of modern men and women.

"Oddly enough, bird families also tend to have stay-at-home dads. In more than 90 percent of bird species, both parents share the care of their young. This arrangement probably began, at least for most birds, when males started staying around the nests to protect helpless babies from predators. 'A flightless bird sitting on a nest is a very vulnerable creature,' explains evolutionary biologist Richard O. Prum of Yale University. Some birds, though, might have inherited their particular form of fatherhood from dinosaurs. Male theropods, a close relative of birds, seem to have done all the nest building, just as male ostriches do today. That doesn't  mean everything was on the up and up. A female ostrich will lay an egg in the nest of her mate, but usually a different male fertilizes it. 'There's a loose relationship,' Prum says, 'between paternal care and paternity.' "


Brendan Borrell


"Origins: Going Back to Where the Story Really Starts"


Scientific American


August 2010


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