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Old Feb 20th, 2003, 11:22 PM        Sex and the single monkey
What I would consider legitimate debate on evolution -- not the legitimate crap that creationists ballyhoo:


Sex and the single monkey

Feb 20th 2003 | DENVER
From The Economist print edition

Darwin's theory of sexual selection is under attack. The first of four reports from this year's meeting of the American Association for the Advancement of Science

HOW the peacock got his tail is one of evolutionary biology's best-known fables. It was first told by none other than the master of evolutionary theory himself: Charles Darwin. It is, Darwin said, all down to the fickle, female peahen. Because she prefers to mate with males with the flashiest tails, large-tailed males have more offspring.

What is less well known is that this theory of sexual selection was created as something of a fudge. Darwin proposed it in response to criticism of his broader theory of evolution by natural selection. That explained how an animal (such as a giraffe) became adapted to its environment through natural variations between individuals. Different neck-lengths in giraffes may confer an advantage on
those with the longest necks.

The problem with this theory, said Darwin's critics, is that it does not account for animals such as the peacock, the stag beetle and the mandrill (illustrated above), whose males have elaborate and bizarre traits. Far from being adaptations to their environment, these showy traits seem likely to be a disadvantage.

Thus, to explain variations between the sexes, Darwin put forward the theory of sexual selection. Females, he said, are the choosy sex; males compete to win female attention. Evolutionary biologists later came to believe that this difference arose from the different size of the gametes—sperm and eggs. Because female gametes are larger than male gametes, females invest more as parents in producing them and so are pickier in their choice of a mate. Males, on the other hand, produce cheap sperm and are promiscuous.

Everybody's doing it
The problem, says Patricia Gowaty, of the University of Georgia, is that the real world does not work like this. At this year's meeting of the American Association for the Advancement of Science (AAAS), in Denver, she explained that her experiments with a number of species, in particular fruit-flies and mice, show that males can be just as picky about their sexual partners as females. Joan Roughgarden, of Stanford University, points out that female monkeys often solicit males and are rebuffed. Why should this be, she asks, if sperm are so cheap?

What worries the minority of scientists who are openly challenging sexual-selection theory is that it is unable to account for much of the diversity of sexual behaviour that exists. If, for example, as sexual-selection theory assumes, mating is primarily about sperm transfer, why do some animals mate between a hundred and a thousand times more often than is needed for conception alone? For animals with strong social structures, the answer could be that mating is a public symbol with social consequences. It is used to create and maintain relationships and alliances, and also to obtain sexual gratification.

Dr Roughgarden, however, believes that the basic mistake is to think that a difference in the size of sperm and eggs translates into differences in behaviour and life history. She says that there are many ways in which animals refute the predictions of sexual selection. For one thing, some fish can make both eggs and sperm during their lifetime, so it is difficult to say categorically that an individual is male or female. Even in such fish as the blue-gilled wrasse, whose biological sex is determined at hatching, gender roles (ie, the behaviours typically associated with one sex or the other) are not.

For, besides fish that behave like “normal” males and females, there are “feminised” males—fish that look like females but have male gametes. These reproduce by helping dominant males to mate with females. In doing so, they gain more reproduction opportunities themselves.

The society of blue-gilled wrasse is by no means the most complicated in sexual terms. Animal societies with up to three male genders and two female genders have been described. Even when only two genders exist, there are cases where male choice of females is the norm. For example, sea-horse males incubate the young in a special pouch and thus provide parental investment that is worth competing for if you are female.

Most troubling, perhaps, to the theory of sexual selection, is the high incidence of homosexuality. Homosexual behaviour in animals, though well demonstrated in the literature written by scientists who actually observe what animals get up to, has tended to be glossed over by theoreticians. But Paul Vasey, a researcher at the University of Lethbridge in Alberta, Canada, has spent many years studying both theory and practice in Japanese macaques.

Female macaques often form homosexual consortships. These are temporary but exclusive relationships that involve frequent sexual activity. Females in a consortship will mount each other tens or hundreds of times. In one group that Dr Vasey observed, females mounted each other as often as once every two minutes. Yet his observations suggest these consortships serve no adaptive function. He has spent many years testing hypotheses that might explain the behaviour, such as alliance forming, the relief of social tension and the communication of dominance. There is, he says, not a shred of evidence for any of them. Female mounting behaviour may have evolutionary roots, but he reckons the reason for it now is sexual gratification. That gratification is involved is known because when a female mounts another female she thrusts her pelvis against the mountee and masturbates her clitoris using her tail.

This activity, of course, excludes males. In one study, Dr Vasey found that when male monkeys courted a female involved in a homosexual consortship, 95% of such females rebuffed him and chose to remain with their girlfriend. This suggests, he says, that it is not simply males who are competing for sexual partners, as Darwin's theory predicts, but both males and females. And homosexual behaviour is documented in at least 15 other species, including Canada geese, gorillas, chimpanzees and humans.

Such examples may not be enough to topple sexual selection, and it is likely that this part of Darwin's theory does indeed hold good for many species. But as Dr Roughgarden warns supporters of that theory, although any one of these problems with it might be overlooked, the “sheer number of difficulties is hard to deny. If these are not enough to falsify sexual-selection theory, then what would be?” Sex, it seems, has come a long way since Darwin.
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Old Feb 21st, 2003, 12:20 AM       
thanks for posting this

Anyway I swear I am a fish. Chicken of the sea indeed
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Old Feb 21st, 2003, 12:44 AM       
You can make both eggs and sperm?

Another neat article, this one's from Nature, a few years back:


Counting the cost of sex
Henry Gee reports on a possible solution of one of the great puzzles of biology: why did sex evolve?
16 March 2000

Sex is an expensive business. There's more to it than flowers, extravagant nights out, school fees and divorce: sex can cost lives and destroy whole species. Sex is so expensive, in fact, that some evolutionary biologists have wondered how so many species can afford such a dangerous luxury -- or even how it could ever have evolved in the first place. Now a team of British researchers offers an explanation.

It's all a matter of perspective. When evolutionary biologists talk about sex, they are talking specifically about sexual reproduction, and rating it against the alternative strategy of asexual reproduction -- simply making clones of oneself.

On the face of it, asexual reproduction looks like a sounder strategy for propagating a species. After all, every member of an asexual species can clone itself as much as it likes, whereas in a sexual species only females have babies. Males are just baubles that lounge around and play golf. Females have to do twice as much work as a member of an asexual species just to keep numbers up. By rights, asexual species should wipe out sexual ones, simply by weight of numbers.

Yet sexual species are everywhere. They are not driven to extinction by reproductively more efficient (if less interesting) asexual clones. This is why evolutionary biologists are hung up about sex.

The usual explanation is that the inherent variation of sexual species more than makes up for the cost of indigent males. When you send in the clones, one looks a lot like another. Sex, on the other hand, shuffles parents' genes, and keeps offspring varied so that sexual species maintain flexibility in the face of changing circumstances.

But there's a catch: variation is an investment that matures over many generations, whereas the cost of males is immediate. Asexual species would 'win' long before sexual species' variation had a chance to make itself felt.

C. Patrick Doncaster and colleagues from the University of Southampton, UK, have found a way out of the dilemma, by looking at how sexual and asexual species would compete in an environment of limited resources: much like real life, in fact.

They have used a computer simulation to model a situation where sexual and asexual species compete for the same resource. The asexual species breeds more than the sexual species, and corners more of the resources. Conventional wisdom would say that the asexual species would then breed more and more, driving the sexual species to equilibrium. But that, the group report in Nature1, does not happen.

The reproductive advantage of asexual species, it turns out, is not as great as biologists had imagined. The reason lies with the monotony of clones. Every cloned individual looks and behaves very much like every other, so they tend to compete for resources far more intensively with each other than with members of sexual species. Second, clones tend to have much more specific preferences than individuals of sexual species. Conversely, because sexually reproducing individuals are varied, they compete less intensively with each other, and can exploit a much wider range of resources. These factors take the heat off sexual species.

So asexual species do not inevitably drive sexual species to extinction. Instead, the two reach an equilibrium, a kind of uneasy balance in which the asexual species' greater capacity for reproduction is countered by its own monotony. This may allow sexual species to invest in their secret weapon -- their own variation -- against the day when circumstances change and they can seize supremacy.

Doncaster, C. P., Pound, G. E. & Cox, S. J. The ecological cost of sex. Nature 404, 281 (2000).
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Old Feb 21st, 2003, 12:47 AM       
very interesting read.
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Old Feb 21st, 2003, 12:50 AM        Whoa...
I dunno, I was kind of hoping this was going to be some kind of love advice for AChimp.
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Old Feb 21st, 2003, 12:53 AM       
the second article seems a lil down on d00ds. o..O or mebbeh im imagining things. still fun to read tho.
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Old Feb 21st, 2003, 12:54 AM       
You can make both eggs and sperm?

You like that don't you!!!

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Old Feb 21st, 2003, 12:56 AM       
They did a study with peacocks recently.. where the males who "got the most ass" had their tail feathers trimmed.... this resulted in less sex for the males until their feathers regrew.

A similar study with lions proved that males with darker neck hair were chosen over those with a lighter hair. After losing a fight, a lions hair actually lightened. Proving that the color of the hair has to do with the lions ability to protect, provide, and whatnot.

As for Asexuality... Due to imbreeding, it is never the only source of reproduction.
Out in the open.
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Old Feb 21st, 2003, 01:21 AM       
The first article is relevant to the supposed "unnaturalness" of human homosexuality and other "deviant" sexual behavior. Forgot to mention that earlier.
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Old Feb 21st, 2003, 07:19 AM       
In one group that Dr Vasey observed, females mounted each other as often as once every two minutes.
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