Is there more than one definition of natural selection?

Then it isn't sexual selection. At least not sexual selection in the sense Darwin proposed, and later biologists perfected. You seem to be talking about a completely different phenomenon entirely. A thread (Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution) has been had, but perhaps it might be an idea to start a new thread dedicated to sexual selection and what it is?

While I certainly do agree that some kinds of sexual selection can lead to evolution by NS, I cannot agree that sexual selection and NS are the same thing. There is no reason I know of that requires sexual selection to automatically invoke NS in a population.I don’t really know if anyone has even postulated this before, so here goes nothin' . Why couldn’t sexual selection be a means for a population to avoid NS? If sex was invented as a means for a genome to avoid its genetic parasites, then why couldn't sexual selection have been invented as a means for a population to avoid the trouble of NS? Hey, if you've got an allele for a big, ugly nose, who's going to want to mate with you? Sexual selection, then, would certainly not seem not to favor NS in the direction of big, ugly noses. Ay?”HM

So you are postulating that big noses are selected against. That is natural selection. Other selective forces (such as survival) may be acting against this selection and we see a compromise. We see this in reverse all the time. Female peacocks may favour even more extravagant tails - a selection pressure acting to increase extravagance, but the survival selection is acting to keep the tails as practical for survival as it can.Survival pressures act against one another - the cheetah would like to be able to run faster, but the costs of doing so may be too great - and thus the two pressures reach an equilibrium Sexual selection does not invoke natural selection. Sexual selection is natural selection. Sexual selection is just the selection for genes which code for a trait that directly increases the ability of an individual to attract a mate (or fight for mating rights etc etc). It is just natural selection with regards to a certain kind of trait. It gets special mention because of course, natural selection as you so often say, is about differential reproductive success - so any traits which directly help an organism influence their chances of reproducing would be sexual selection.

Let's test my proposition that there can be sexual selection without NS:In a hypothetical population of 100 individuals”50 males and 50 females”the good-looking ones go first and rest mate up with what’s left, but everybody is happy. That’s sexual selection, pure and simple. Now, the good-looking ones and the bad-looking ones have equal fecundity in this hypothetical population; each couple has exactly one girl and one boy. Everybody in the population has reproduced with equal success. So, in this scenario, there was sexual selection without NS.If you can’t eliminate this scenario from the realm of possibilities, then you can’t prove that sexual selection is the same thing as NS.”HM

There was no sexual selection, though, if mates didn't prefer to mate with "sexier" individuals.In your example, everyone enjoys equal mate access, so no sexual selection actually occurred. Reproductive opportunity was identical throughout.You've failed to actually present an example of sexual selection, so no, this example doesn't prove that you can have sexual selection that doesn't result in any natural selection.

Now show that there was no change in hereditary traits ... the change in hereditary traits that results shows that natural selection occurred.Enjoy.Edited by RAZD, : .

---

Join the effort to unravel AIDS/HIV, unfold Proteomes, fight Cancer,
compare Fiocruz Genome and fight Muscular Dystrophy with Team EvC! (click)

---

we are limited in our ability to understand
by our ability to understand
RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

You seem to be getting sexual selection confused with mate choice, they are not one and the same thing, although they are obviously closely connected. What your example shows is mate choice leading to assortative mating for 'good-looks', not sexual selection.TTFN,WK

crash wrote: No, crash, it’s purely sexual selection. Reproductive opportunity does not equal fecundity, and NS is determined on the basis of fedundity, not mate selection.It’s just like when you were in high school. You and all the other bad-looking boys wanted to go out with Judy, the popular and good-looking cheerleader. But only Tommy, the popular and good-looking football player, got to go out with her. Meanwhile, you and your bad-looking buddies, who were too chicken to go out for football, had to be satisfied with the uglier girls. Nevertheless, everybody got dates for the Prom”even you with your pimples and pigeon chest. But you all had the same kind of reproductive equipment.That’s sexual selection. If NS were to occur in your high school population its fecundity would have to show a measure of differential reproductive success. And that critical issue, if it were to apply to your high-school population, would have to be decided later”nine moths later, in fact.Now, it was discovered later by your Principal that every single one of those girls, whether they were good looking or not, got knocked up in the parking lot that night after the Prom. Yup, and nine months later they all had single births, producing equal numbers of boys and girls.You see, there was sexual selection for the Prom, but with evenly distributed fecundity, there no NS occurring in the population nine months later at the maternity ward. Thus this hypothetical scenario demonstrates that sexual selection and NS are two different things.”HM

WK wrote: How do you differentiate them?”HM

RAZD wrote: To show you that, RAZD, there would need to be an elapse of time while gestation occurres. Only after that can a population's fecundity be measured. Any conclusion about NS would have to await that necessary sampling of the extant population.”HM

Sexual selection is normally considered to encompass both indirect competition for mates , i.e. by making oneself a more desirable choice of mate, and direct competition for mates by physical contests.Apart from this distinction your own example shows how some forms of mate choice may not lead to any selection, in the evolutionary sense, even though the choice represent 'selection' in the commonplace usage of making a choice.This is mostly due to the highly artificial set up of your scenario. Almost any imbalance in it would in fact lead to sexual selection occurring, provided the attractiveness of the individuals had at least a partially genetic basis.TTFN,WK

No, we can be pretty sure that with only one child per couple that only half of the genes of the population will be transmitted to the offspring. This type of change would normally be labeled genetic drift, however in this case it is caused purely by the choice to have only one child per couple. Thus the choice to have only one child per couple resulted in a change in the hereditary traits in the population.In a normal population the number of children would vary (as would the chosen mates) and this too would be natural selection.So you have mate selection (no sexual selection) and natural selection. Not what you were thinking eh?Enjoy.

---

Join the effort to unravel AIDS/HIV, unfold Proteomes, fight Cancer,
compare Fiocruz Genome and fight Muscular Dystrophy with Team EvC! (click)

---

we are limited in our ability to understand
by our ability to understand
RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

WK wrote: Nah. My scenario is entirely possible, if not probable.I think there is an essential difference between:1. Differential mating success amongst individuals of a population,and2. Differential reproductive success amongst individuals of a population.There could easily be a scenario in nature where one occurs without the other. That's why they are different things.I'm blaming Hardy & Weinberg for my recalcitrant position on this, because their equation for alleleic equilibrium assumes necessarily that mating success is equal amongst all invididuals of a population.”HM

RAZD wrote: All right, let's go to the source to see if Darwin differentiates between sexual selection and natural selection? Let’s go to The Origin of Species (pp. 56 & 57 of my edition)”:

quote:

---

Inasmuch as peculiarities often appear under domestication in one sex and become hereditarily attached to that sex, so no doubt it will be under nature. Thus it is rendered possible for the two sexes to be modified through natural selection in relation to different habits of life, as is sometimes the case; of for one sex to me modified in relation to the other sex, as commonly occurs. This leads me to say a few words on what I have called sexual selection. This form of selection depends, not on a struggle for existence in relation to other organic beings or to the external conditions, but on the struggle between the individuals of one sex, generally the males, for the possession of the other sex. The result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection.

---

I rest my case.”HM

Just saying... Doesn't make it true and you haven't provided a scrap of argumentation to suggest it is in the least credible. Can you give us a real life example of any such population, since it is so probable?How exactly does ... Not equate to a differential in reproductive success? What has hardy-Weinberg got to do with anything. The whole point of those equations is that they apply to ideal populations of effectively infinite size and which aren't undergoing selection and which mate randomly.Your model population makes no sense unless your couples only reproduce exactly enough to replace themselves and is going to rely heavily on inbreeding. Any imbalance in the population screws up your approach which relies on artificial constraints to maintain an equilibrium while including non-random mating.TTFN,WK