Talk:Sexual selection

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1 Main Picture
2 R & K selection
3 Plants as well
4 More info on Wallances gripes
5 Notes on Geometric Progression Theory section
6 Mechanisms
7 epigenetics
8 prudery??
9 Chimpanzee theory
10 problem sentence?
11 Largest vertebrate SSD?
12 Rare/Complicated/Unneeded wording
13 references
14 Sexual Selection and intelligence in humans
15 Difficult paper reference
16 peacock predator distraction hypothesis
17 Female sabotage

[edit] Main Picture

I know the picture now is a plate from Descent, but can we get something that better exemplifies the situation then a black and white drawing? Color being such a key trait, shouldnt it be color!? 'African long tailed widow bird'? --Mike 04:55, 8 June 2006 (UTC)

[edit] R & K selection

"K- and r-selection One of the most famous types of sexual selection is selection by number of offspring.

Some animals, like human (sexually mature after adolescence) and Northern Gannet (5-6 years), produce few offspring. Others reproduce quickly, but unless raised in an artificial environment, most offspring do not survive to adults. A rabbit (mature after 8 months) produces 10 - 30 offsprings per year, a Nile Crocodile (15 years) produces 50, and a fruit fly (10-14 days) produces up to 900. Both strategies can be favoured by evolution: animals with few offspring can spend time nurturing and protecting them, hence greatly decreasing the need to reproduce; on the other hand, animals with many offspring do not need to spend parental energy on nurturing, allowing more energy to be devoted to survival and more breeding.

These two strategies are known as K-selection (few offspring) and r-selection (many offspring). (The letters "r" and "K" derive from the names used in the mathematical formulae in the original theory). Which strategy is favoured depends on a wide range of circumstances"

This was removed?! It should have been at least condensed and intergrated. --Mike 04:11, 8 June 2006 (UTC)

[edit] Plants as well

It should be noted that sex.sel. manifests itself in plants as well, i.e. pollen discrimination. --Mike 22:07, 7 June 2006 (UTC)

[edit] More info on Wallances gripes

"sexual selection were opposed strongly by his "co-discoverer" of natural selection, Alfred Russel Wallace, though much of his "debate" with Darwin took place after Darwin's death. Wallace argued that the aspects of it which were male-male competition, while real, were simply forms of natural selection, and that the notion of "female choice" was attributing the ability to judge standards of beauty to animals far too cognitively undeveloped to be capable of aesthetic feeling (such as beetles). Historians have noted that Wallace had previously had his own problem with "female choice": he had been left at the altar by a woman of a higher social class."

Here is acutal text from him, and Fishers retort..

In butterflies the weeding out by natural selection takes place to an enormous extentin the egg, larva, and pupa states; and perhaps not more than one in a hundred of the eggs laid produes a perfect insect wihch lives to breed. Here, then, the importance of female selection, if it exists, must be complete; for, unless the most brilliantly coloured males are those which produce the best protected eggs, larvae, and ppupae, and unless the particular eggs, larvae, and pupae, which are able to survive, are those which produce the most brilliantly coloured butterflies, any choice the female might make must be completely swamped. If, on the other hand, there IS this correlatin between clour development and perefect adaptation at all stages, then this development will necessarily proceed by the agency of natrual selection and the general laws whioch determine the production of clour and of ornamental appendages. --Wallace

It should be observed that if one mature form has an advantage over another, represented by a greater expectiaton of offspring, this advantage is in no way diminished by the incidence of mortalityin the immature stages of development, provided there is no associeation between mature and immature characters. --R.A.Fisher --Mike 21:47, 7 June 2006 (UTC)

[edit] Notes on Geometric Progression Theory section

(THIS THREAD IS A WORK IN PROGRESS)
This is to be added later in as articulate a manner as possible, with explination for the lay reader.

Fisher wrote about this in a game theoretic context, but it was really a problem to be treated by population-genetics theory. As Lande(1981) did, which I think was based off of O'Donald(sp?) who was a student of Fisher. J.M. Smith goes over this in EatToG, p131-137.

R.Lande's (1981) paper: http://www.memeoid.net/books/Lande/RLande.pdf

ROUGH notes on Landes Model, most of this is regurgitated JM Smith:

Figure 1

Figure 2

Figure 3

In this model it is assumed all females can mate and that there is no parental investment on the part of the male. The result is that there is no direct selection on females, since all females have the ability to mate and genes for ornimentation do no express themselves in females where they could impose bionomic survival effects. However, genes effecting female preference, y, will fluctuate in frequency since assortative mating creates genetic covariance between z and y; when z changes so will y. Males with genes for a large z tend to have genes for high y, and visa versa, (as in the Peacock example). The fitness of a male, with trait z, then depends on his chance of surviving to breed, $\phi z\,$ , and on his success at mating (which is dependant on the distribution of female preference, as well as the trait values of other males).

Let

$z\,$ = messure of some male trait, such as tail length,

$y\,$ = a messure of the degree by which a female preferes z

and

$\phi z\,$ = the probabilty that a male,with trait z, survives to breed, based on the bionomic situation and the effects of Natural Selection on z,

$z_{opt}\,$ = suppposed optimal value for z with survival probablity falling off on either side

then

$\psi(z|y)\,$ = a function proportional to the chance that a male bearing tait z, will be chosen by a female of preference y

Thus, if there are two types of males z₁ and z₂ in proportions p and 1-p. The probability that a female with a preference of y will mate with the male bearing z₁ is

$p\psi(z_1|y)/[p\psi(z_1|y)+(1-p)\psi(z_2|y)]\,$

pψ(z|y) takes into account the number of males, (p), of the selected type in comparison to other choices, (1-p); where as ψ(z|y) does not take the numbers of types of z into account, but simply defines the degree of compatibility between z and y.
The probability that a female of type y will mate with male z₁ is equal to the number of males of type z₁ times the degree of compatibility between z₁ and y, divided by the total probability of y mating with both types of z, taking into consideration the compatibilty between y and each type of z.

Lande considered three types of functions for preference:

(i) Progressive preference: Females prefer large z, but each differ in the degree.

$\psi(z|y)=exp(yz)\,$

Preference is a simple function of the natural base to the power of yz(the combined degree of preference and trait). y being a predetermined constant for a female, she will prefer the largest variable, z, possible, since her taste times the variable z is the power that raises the base.

(ii) Absolute preference: A y female prefers a male of tail length z=y, of the same degree as her taste, and the desire to mate decreases off each side of this value. k = A constant.(EXPLANATION FOR k ?!?)

$\psi(z|y)=exp[-k(z-y)^2]\,$

(iii) Relative preference: A y female prefers a male of a tail length greater then the population mean, $\bar{z}$ , by an increase of y.

$\psi(z|y)=exp\{-k[z-(\bar{z}+y)]^2\}\,$

The first conclusion from this, that genes for a degree of z tend to be accompanied by genes for high y, is that there is not a single equilibrium point but a line of possible equilibria. Each value of $\bar{y}$ has a commensurate value of $\bar{z}$ not having to correspond with $z_{opt}\,$ . Additionally, each value for an ornamentation will have a certain degree of Natural Selection acting on its bionomic effects, and from this we can find a value of female preference to balance those effects. Secondarily, since linkage equalibrium is created from assortive mating, there is indirect Natural and Sexual Selection acting on female preference.

When a population does obtain a point along the line of equilibrium, all kenetic force created from the exponetial situation which moves it along its line of motion, has disipaited (See Figure 3). Equilibrium is reached when the forces of Natural Selection acting againt negative effects on classical fitness, $\phi z\,$ , cancel the benifitial effects of Sexual Selection on reproductive fitness of z, $\psi(z|y)\,$ .

Figure 2 illistrates the frequency distribution of z, for a absolute preference of $\bar{y}$ , under the different selective pressures.

(a) The distribution of zygotes containing z, prior to the effects of selection. A function of $p(z)\,$ ,
(b) Natural selection pressure against the bionomical effects of different trait z values(not a population distribution). A function of $\phi z\,$ ,
(c) The effects of Natural Selection against z, (b), over the distribution of $p(z)\,$ , (a). The distribution of mature males. A function of $p(z)\phi(z)\,$ ,
(d) The effects of the optimal value of $\bar{y}\,$ against different values of z. Simular to (b) (not a population distribution). A function of $\psi(z|\bar{y})\,$ ,
(e) the frequency distribution of mature mating males with z after the effects of Natural Selection(c) and Sexual Selection(d) on the value of z. A function of $p^*(z)\psi(z|\bar{y})\,$ ,

-the line of equib is determined by NS pressure

(THIS MIGHT BE BETTER PLACED AFTER FIGURE 5? EXPLINATION - WITH THE CURVED LINE OF EQUALIBRIUM)
The results will sort of look sort of like Pun.Equi. , i.e. large spurts of ornimentation development until the brick wall of NS stops it. Maybe this is why Gould was so bloody confused ;)

"It is important to notice that the conditions of relative stability brought about by these or other means, will be far alonger duration than the process in which the ornaments are evolved. In most existing species the runaway process must have been already checked, and we should expect that the more extraordnary developments of sexual plumage ere not due like most characters to a long and even course of evolutionary progress, but to sudden spurts of change." R.A.Fisher (1930)

--Mike Spenard 21:34, 18 June 2006 (UTC)

[edit] Mechanisms

There should be coverage of different poroposed mechanisms: Fisher's run-away process, direct benefits, and sensory exploitation should be included.

Also, the idea that female choice is more common, or strong, in more intellignet species is bunk.

--Pete Hurd

[edit] epigenetics

I removed the following:

The field of epigenetics is broadly concerned with the competence of adult organisms within a given sexual, social, and ecological niche, which includes the development of mating competences, e.g. by mimicking adult behavior.

This is idiosyncracy. "Epigenetics is the study of heritable gene expression that occurs without a change in DNA sequence. " http://biology.ecsu.ctstateu.edu/courses/molgen/Epigenetics

AxelBoldt, Sunday, April 14, 2002

[edit] prudery??

The following statement is made in the article:

"Ambiguous combinations of both types of selection acting on the same traits is usually referred to as natural selection. Some accounts refer to natural selection as strictly ecological and as distinct from sexual, but this appears to be a holdover from Victorian sexual prudery, and further fails to distinguish combinations of the two "natural" processes from other concepts of evolution, such as evolution of societies."

It's true that by 'natural selection' Darwin meant, essentially, 'ability to survive'. As far as he was concerned sexual selection was a different concept, introduced to explain phenomena such a peacock tails, which would seem to be a hindrance rather than a help to survival. What does this have to do with Victorian 'sexual prudery'. As for the point about social evolution, how is this relevant? Darwin didn't even use the term 'evolution' much, so this is surely an irrelevance - a mere quibble over terminology, not meaning. Paul B 16:51, 21 March 2005 (UTC)

Seconded. Prudery has got nothing to do with the "split" between natural and sexual selection. And I've no idea what that bit about "evolution of societies" is on about. --Plumbago 08:25, 23 Jun 2005 (UTC)

Sorry for the inadvertant resurrection of the phrase in my edit yesterday. I had recently downloaded the markup of the page, and thought I was editing it (offline), but I accidentally used a version I had stored a few months ago as the basis of my edit. It included the phrase, and it's one of the things I had decided not to change. I'll confirm that no other recent changes were similarly affected.--Johnstone 23:00, 23 Jun 2005 (UTC)

[edit] Chimpanzee theory

I have removed the following since it lacks a reference:

"It has subsequently been theorized that this may have evolved because males tend to prefer to mate with females who are relatively youthful and healthy (and who are thus more likely to be fertile and survive pregnancy), and hairlessness is generally indicative with youthfulness. The general physiological resemblance between adult humans and adolescent chimpanzees (adult humans resemble young chimpanzees to a greater extent than they resemble young humans or adult chimpanzees) has recently been proposed as supportive evidence of this (the supposition being that the selection occurred at a time when the ancestors of humans resembled chimpanzees.)" [Includes my minor copyedit.]

--Johnstone 01:38, 23 Jun 2005 (UTC)

[edit] problem sentence?

I haven't read Fisher's stuff, but logically, didn't he mean the following? (My additions bolded)

However, 'sexual selection' typically refers to the process of female choice. R.A. Fisher pointed out that this female preference could be under genetic control and therefore subject to a combination of prior natural and sexual selection just as much as the qualities of the males that are actually 'preferred'.

Tony 00:40, 9 March 2006 (UTC)

[edit] Largest vertebrate SSD?

A larger sexual size dimorphism in vertebrates has been documented.

Text from this article - "The largest sexual size dimorphism in vertebrates is the shell dwelling cichlid fish Neolamprologus callipterus in which males are up to 30 times the size of females."

Text from Photocorynus spiniceps article (http://en.wikipedia.org/wiki/Photocorynus_spiniceps) - "The male spends its life fused to its much larger female counterpart, which in some species are up to half a million times greater in mass."

Apparent source - "Dimorphism, parasitism, and sex revisited: Modes of reproduction among deep-sea ceratioid anglerfishes", Theodore W. Pietsch, Ichthyological Research (2005) 52(3): 207-236. http://uwfishcollection.org/staff/Dimorphism.pdf

-- Sharon Rose

Hmmm, the angler fish example is a bit exceptional due to the parasitic life-history. It's worth mentioning, certainly, but I wouldn't replace the callipterus example. In the callipterus, case both fish are independent, fully functioning adults throughout the life cycle. It's not clear to me whether the half million times mass difference (60X length asymmetry) refers to male mass before or after fusion and metamorphosis (not that it appears from this paper that they change much in size, but I seem to remember males of some of the anglerfish introgressing into the female and metamorphosing until they're pretty much nothing but testicular tissue living within the female's body cavity. Pete.Hurd 21:10, 22 March 2006 (UTC)

[edit] Rare/Complicated/Unneeded wording

"less limiting sex (typically males)" what on earth does this mean?? Jackpot Den 22:28, 29 March 2006 (UTC)

"...and this difference in initial investment creates differences in variance in expected reproductive success and bootstraps the sexual selection processes" Someone please reword this horribly incoherent sentence. What do you mean by differences in variance? —The preceding unsigned comment was added by Fritsky (talk • contribs) 02:44, 24 May 2006.

In a static situation organisms will fluctuate around a mean value for a character, this is variance. To create differences in variance, is to diverge from the average value of a trait.

The differance(s) brought about in the 'intitial investment' breaks this static situation, causing divergence from this mean, and the creation of difference in variance between the two sexes, for a trait. --Mike 17:34, 7 June 2006 (UTC)

[edit] references

The article has improved greatly recently, but I miss one thing, and that is references to actuall sources. Would it be possible to add those? -- Kim van der Linde ^{at venus} 21:50, 7 June 2006 (UTC)

Hi Kim, feel free to make any suggestions for references(within the article text or in the References Section at the bottom?). Glad to see someone noticed the work ive done on trying to improve this article :) --Mike 04:46, 8 June 2006 (UTC)

[edit] Sexual Selection and intelligence in humans

I recently read "The Ancestors Tale" by Richard Dawkins. In that, as I understood it, he was suggesting that there is some thought that intelligence in hominids may well have been driven by sexual selection. Could be a useful addition in the sexual selection in humans section? Of course the down side is that it may be a contentious issue to some.

JohnT 12:19, 13 June 2006 (UTC)

I suppose it may be worth noting, but the article should focus on the general principles and processes.. that and there is no shortage of theories on what caused human intelligence.--Mike Spenard 19:24, 13 June 2006 (UTC)

[edit] Difficult paper reference

I'm severely unhappy with the following passage:

Canadian anthropologist Peter Frost, under the aegis of University of St Andrews, published a study in March 2006 in the journal Evolution and Human Behavior^[1] that says blond hair evolved at the end of the last Ice Age by means of sexual selection. According to the study, northern European women evolved blonde hair and blue eyes at the end of the Ice Age to make them stand out from their rivals at a time of fierce competition for scarce males. The study argues that blond hair originated in the European region because of food shortages 10,000–11,000 years ago. Almost the only sustenance in northern Europe came from roaming herds of mammoths, reindeer, bison and horses and finding them required long, arduous hunting trips in which numerous males died, leading to a high ratio of surviving women to men. Women with blond hair were more attractive to their mates and thus there was evolutionary pressure that increased the number of blonds.

So males died because of food shortage, but women...? This is a ridiculous study since it is well known that blondes have lighter coloured skin which leads them to produce more vitamin D than dark-haired people under the same conditions. It is a no-brainer that as people migrated North after the ice ages, they became exposed to lower light levels, and needed to produce more vitamin D, shortage of which can lead to medical conditions such as those listed here. I do not see how the study is notable within the scope of the article, and I generally strongly advise against including material more recent than five years old as part of avoiding original research. - Samsara (talk • contribs) 16:16, 13 June 2006 (UTC)

I agree on this as well, its a similar objection to the one I voiced above, its an idea without much empirical evidence and peer validation. This article should stick to what is solid. I'll work on going thru the rest of the article for this sort of thing when I finish with the Geom.Prog. section. --Mike Spenard 19:30, 13 June 2006 (UTC)

[edit] peacock predator distraction hypothesis

This edit [1] by User:Corvun "added note that the bright color of male birds may distract predators from females and offspring", seems kooky. It ads in part "By distracting predators from his offspring and giving said predators a satisfying meal, he greatly increases his offspring's chances of surviving until reproductive age." Perhaps I missed it, but I've never heard this theory being advanced in the literature. Given what little I know about the peacock's mating system, I find it really hard to believe that it's true. The original edit ended with "And since males are far more expendible in terms of population dynamics than females, distracting the attention of predators away from females and attracting attention to males bennefits the gene-pool as a whole." which waves all kinds of red flags. I think the whole paragraph, in it's present form, should go unless reliable sources are provided. Pete.Hurd 20:58, 26 November 2006 (UTC)

[edit] Female sabotage

The 1998 article cited to support the Female Sabotage hypothesis paragraph, has been cited a total of two times (once incorrectly) since it was published. The 2005 paper (mentioned but not cited) does not appear in the ISI database. This appears to be a relatively non-notable piece of work given undue emphasis. Pete.Hurd 22:42, 26 November 2006 (UTC)

OK, I found the 2005 paper. Abraham JN Insect choice and floral size dimorphism: Sexual selection or natural selection? JOURNAL OF INSECT BEHAVIOR 18 (6): 743-756 NOV 2005, Times Cited: 0. It's one of the two papers to cite the 1998 article, (the other is Bertini A, David B, Cezilly F, et al. Quantification of sexual dimorphism in Asellus aquaticus (Crustacea : Isopoda) using outline approaches BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY 77 (4): 523-533 DEC 2002, Times Cited: 2. Pete.Hurd 02:19, 27 November 2006 (UTC)

Doh! there it is in the references section... Pete.Hurd 02:47, 27 November 2006 (UTC)

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