polygamous past, asexual future ?

... look out, boys ;)

Published on September 23, 2004 By mignuna In Pure Technology

By Jennifer Viegas, Discovery News

Three recent studies on sex reveal that polygamy holds biological benefits so dominated human history that it is imprinted in our genes; but that asexuality appears to be a relatively new evolutionary phenomenon that could, in the future, be favored by natural selection.

Together the studies help to explain why sexual reproduction amongst all creatures on Earth is so widespread, and yet why some animal, fish, bacteria, and insect species can reproduce asexually.

In the first study, William Hughes of the University of Sydney and colleague Jacobus Boomsma of the University of Copenhagen studied Panamanian ant colonies. The researchers found that, despite the costs of sex, such as risk of predation, female ants with many male partners had healthier progeny than monogamous females.

The scientists made this determination after infecting groups of the young ants with a fungal parasite. Ants with mothers who slept around tended to survive better than those with monogamous moms.

"The results of our study suggest that social insect queens may benefit from mating with multiple males by making their colonies more genetically diverse and therefore more resistant to disease," said Hughes.

Humans in history appear to have fooled around a lot as well.

University of Arizona in Tucson scientists studied DNA from Y chromosomes, which are passed from father to son, and mitochondrial DNA, which is passed from mother to daughter. The DNA came from 389 individuals representing a number of populations worldwide, including the Netherlands and South Africa.

The researchers discovered that while more men than women are squeezed out of the gene pool, Y chromosome variations indicate that those men whose genes did survive tended to travel and to have multiple female partners.

"We may think of ourselves as a monogamous species, but we're coming from an evolutionary history that's probably slightly polygamous," said Michael Hammer, a research scientist at UA's Arizona Research Laboratories. "If we're shifting toward monogamy, it's so recent it hasn't left an imprint in our genome."

Co-author Jason Wilder, a postdoctoral fellow, added, "The modern version that we generally don't find offensive is that men tend to remarry and have more children much more often than women do."

Some species, however, have the ability to reproduce without males.

Maurine Neiman, an Indiana University biologist, analyzed both asexual and sexual species to determine why sexual reproduction is so widespread. According to her paper, published in the current Animal Behavior, asexual females are new in evolutionary terms, with most species arising within the past 100,000 years.

Neiman contends that all of the asexual species mentioned in her study — certain lizards, fish, rotifers, flies, snails, beetles, roaches, planthoppers, and isopods — descended from sexual ancestors.

Dependence on males for stimulation and hormonal changes appears to curb asexual reproduction in most of these species, which gives sexual species a short-term edge that natural selection appears to favor, according to Neiman.

However, at least one of the animals that she studied, asexual lizards from the Cnemidophorus genus, engage in "pseudocopulatory behavior" with other females and have, she says, become a "striking ecological success."

"As only females can contribute directly to the rate of population growth, a population composed of asexual individuals will have an intrinsic rate of increase that is twice as high as an otherwise identical sexual population," Neiman said.

She adds that “the descendents of an asexual mutant in a population of sexual organisms should thus quickly outcompete the sexual descendents of the source population." So far, this has not happened for most species, since males tend to reject asexuals and dependence on copulatory behavior remains.

Neiman writes, "... the ability of asexual females to escape dominance on copulation will be a function of the rate of mutation to less dependent reproductive physiology following their derivation from sexual populations. Once these alleles (genes) arise, they should be heavily favored, particularly if parthogen (asexual) access to males is limited."

Ellen Ketterson, professor of biology at Indiana University, believes that Neiman's theory and data "are both persuasive." She does not think asexuality has much chance of surviving natural selection because, similar to the Panamanian ant findings, lack of genetic variation makes individuals more vulnerable to parasites.

Ketterson says that many questions remain about asexuals. She asks, "Can these organisms be used to test the ideas about why in ancient life sexuality evolved over asexuality?"

Future research likely will continue to examine why sex remains the rule rather than the exception.

Further reading: Link

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Comments

wuxiaomao

on Sep 23, 2004

haaang on a tick...."asexuality" and "polygamy" are not the same thimg buddy!!

wuxiaomao

on Sep 23, 2004

girl!!

mignuna

on Sep 23, 2004

haaang on a tick...."asexuality" and "polygamy" are not the same thimg buddy!!

um, i'm not sure if you're joking or not, wuxiamao. the article was about the differences between the two, ie:

"polygamy holds biological benefits so dominated human history that it is imprinted in our genes; but that asexuality appears to be a relatively new evolutionary phenomenon that could, in the future, be favored by natural selection".

or

"Together the studies help to explain why sexual reproduction amongst all creatures on Earth is so widespread, and yet why some animal, fish, bacteria, and insect species can reproduce asexually".

vanessa XX

on Sep 23, 2004

wuxiaomao, please read more carefully.

Hmm intresting. I wonder what would happen if we humans were asexual.

mignuna

on Sep 23, 2004

Hmm intresting. I wonder what would happen if we humans were asexual.

XX, i can think of a least a few problems it would solve

vanessa/mig XX

Jay Walker

on Sep 24, 2004

After answering your recent quiz, why does this not surprise me that the species, particularly men, aren't really designed to be monogomous?

JW

mignuna

on Sep 24, 2004

After answering your recent quiz, why does this not surprise me that the species, particularly men, aren't really designed to be monogomous?

jay, i'm guessing that the reason would be that monogamy is a way of unnaturally controlling natural desires ?

mig XX

stevendedalus

on Sep 27, 2004

i'm guessing that the reason would be that monogamy is a way of unnaturally controlling natural desires ?

...unless the love is overwhelming to direct that natural inclination to the ONE.

Myrrander

on Sep 27, 2004

Actually, scientists are postulating that the Y chromosome is decaying, which makes sense, since it is a mutation of the X chromosome in the first place. There have been some studies done with mice that have used genetic material from an egg to fertilize another egg like a sperm would -- thereby making a male-less mammal pregnancy. Of course, no such studies have been done in higher mammals, but it's intriguing anyway.

stevendedalus

on Sep 28, 2004

In light of science it appears that Adam came from Eve's rib [or egg].

mignuna

on Sep 29, 2004

unless the love is overwhelming to direct that natural inclination to the ONE

well, of course stevendedalus

Actually, scientists are postulating that the Y chromosome is decaying, which makes sense, since it is a mutation of the X chromosome in the first place.

thanks, myrrander. that's an interesting point

There have been some studies done with mice that have used genetic material from an egg to fertilize another egg like a sperm would -- thereby making a male-less mammal pregnancy

now there's a thought

Of course, no such studies have been done in higher mammals, but it's intriguing anyway.

i agree, it is. thanks for your comments, myrrander.

In light of science it appears that Adam came from Eve's rib [or egg].

stevevdedalus ! *rolling on floor laughing* ... you !

mig XX

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