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Sexual Selection Explained: Evolution 101 - YouTube

The sexual selection hypothesis offers several empirically testable predictions.

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Directional selection also has a unique effect on the population -- itleads to an evolutionary that changes the mean of the trait from one generation to the next if thetrait has a heritable component. The change in the mean across generationsreflects the pattern of evolutionary change. However, we must ask a questionabout processes that underlie this change.

Introduction to Natural and Sexual Selection

If the action of disruptive selection is relativelyweak it will tend to increase the representation of indivduals in the tailsof the distribution. The distribution will appear flatter and with longertails after selection compared to the distribution before selection. Ifdisruptive selection is relatively strong, it will lead to two distinctmodes which are separated by a valley in which selected phenotypes havebeen removed by selection.

The mitonuclear compatibility hypothesis of sexual selection

Disruptive selection is perhaps the most elusive mode of selection. Despitethe paucity of actual examples of disruptive selection, the process is thoughtto play a major role in the process of speciation or the origin of new species(Templeton, 198X). The action of disruptive selection is much more complicatedthan the action of directional selection in which a single agent of selectionshapes a trait. Furthermore the action of disruptive selection is likelyto be more complicated than stabilizing selection which in many instancesis composed of counterbalancing trade-offs. Disruptive selection acts againstthe individuals in the middle of the range of phenotypes and tends to favorindividuals in the extremes. A simple form of disruptive selection on asingle locus with two alleles where the heterozygous individuals are ata disadvantage relative to the two homozygous classes (). In the case of such underdominance in fitness, selectionfavors the more extreme homozygous classes.

"Neoteny and Two-Way Sexual Selection in Human Evolution" (published in full here) was first published in the Journal of Social and Evolutionary Systems, vol.18(3) pp.257-276, January 1996.

a test of the sexual selection hypothesis.

[8] For "variability" we might replace "volatility" or even "instability." To illustrate this, from 1960 to 1986, the proportion of women attending University of California Medical Schools rose from under five percent to forty percent. Over the same period, the female population of California also started around five percent... and stayed there. Clearly women are learning assertiveness, but being selective about applying it. Males' former near monopoly on violent crime has not shifted, despite all recent changes in the stressful lives of American women. This is not to say that men are automatically bad guys. Rather they appear to show a degree of variability that is exaggerated even among primates. Consider why this high variability makes sense. First, humanity's recent rate of evolution appears to have been rapid, and Darwin showed that selection acts on variability. Among males, especially, a successful sport can pass on new, adaptive traits generously, while omitted male "failures" have little consequence. If this argument smacks of "group selection," careful re-phrasing can put the same idea in context of "selfish genes." Finally, the twin forces of sexual selection and change of reproductive strategy, have very probably contributed to making human males unstable, variable, and perhaps a little "crazy."

In "runaway" sexual selection, the selected trait becomes more embedded and exaggerated with each passing generation, requiring the next wave of the selected sex (usually males) to compete from a new plateau, which amplifies the trait even more, and so on. Even if the degree of exaggeration threatens the viability of the species at large — e.g., the titanic antlers of the extinct Irish elk — this may not abate the driving competition among individuals for reproductive success [10]. The models of R. A. Fisher (1958) long ago showed that evolution of a sexually selected trait, and the preference for it, can strongly correlate, with both accelerating in tandem.

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  • Evolution: Sex: The Advantage of Sex - PBS

    Our findings provide little support for a role of sexual selection in the evolution of musical ability.

  • Evidence for Evolution: An Eclectic Survey

    had proportionally longer necks compared to foreleg length than males when the sexual selection hypothesis …

  • Hypothesis testing - Handbook of Biological Statistics

    Sexual selection is a component of natural selection in which mating success is traded for survival

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Evolution: Sex: Sex and the Single Guppy - PBS

Another way evolution can accelerate is the major exception to natural selection admitted by Darwin, and the one way species can be said to design themselves: Sexual Selection. The bird of paradise and mandrill are vivid examples of what can happen when female choice of "quality" males becomes tied not just to the male's robustness or fidelity, but to some outward and apparently arbitrary physical display — e.g., length of plumage or vividness of color.

Learn how exhibitionism has can have an evolutionary payoff.

What has long escaped discussion are the second-order effects, where "runaway" sexual selection may have resulted in human traits that are as exaggerated as any bird's tail. Nor has there been much investigation of females as of sexual-selection, rather than simply as classical selectors.

The Homepage of Peter J Carroll

While artificial selection is useful for documenting the genetic causesof behaviors and correlations between behavior and other traits, adaptationalhypotheses are bested tested in nature on animals that experience the forceof natural and sexual selection. In his treatise on the , John Endler (1986) considered natural selection a processthat is inseparable the genetic transmission of the successful traits. Thiswould make the detection of natural selection a very difficult task becauseof the huge sample sizes required to assess the genetic contribution tobehavioral traits (see ), combined withthe large sample sizes required to measure selection on a phenotypic trait.

A Site about Three Dimensional Time

Houde was successful in changing female preference by artificial selectionon male coloration. While the differences between high and low male linesis maintained after three generations, the correlated changes in femalepreference that appear in the first generation appear to decay away by thethird generation in some of the lines. A parsimonious explanation for thesepatterns is that selection has eroded additive genetic variation in bothmale color and female preference. Coloration alleles that have become fixedby selection in males reduces the heritability for male coloration. A similareffect might be seen in female preference. However, a genetic correlationbetween male and female preference requires that male perference per sebe heritable. Under conditions of artificial selection, heritability ofmale color should be reduced. While this may be an artifact of laboratoryselection, large population size in nature may maintain high levels of heritabilityin the face of sexual selection. Her results demonstrate the existence ofa genetic correlation between male traits and female preference. Similarcorrelations have been documented for sticklebacks (Bakker 1993) from correlationsamong relatives (e.g., sons and daughters), and from artificial selectionon stalk length in male stalk-eyed flies and correlated changes in femalepreference (Wilkison and Reillo 1994).

Confirmation bias - ScienceDaily

Figure 3.X. Change in orange coloration of male guppies duringthree generations of artificial selection for high (filled circles) andlow (open circles) amounts of orange. Differences between high and low linesare significant after the first generation.

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