sexual selection

Examples of sexual selection in the following topics:

• Sexual Selection

  • Sexual selection, the selection pressure on males and females to obtain matings, can result in traits designed to maximize sexual success.
  • The selection pressures on males and females to obtain matings is known as sexual selection.
  • Sexual selection takes two major forms: intersexual selection (also known as 'mate choice' or 'female choice') in which males compete with each other to be chosen by females; and intrasexual selection (also known as 'male–male competition') in which members of the less limited sex (typically males) compete aggressively among themselves for access to the limiting sex.
  • Sexual selection can be so strong that it selects for traits that are actually detrimental to the individual's survival, even though they maximize its reproductive success.
  • This is an example of the extreme behaviors that arise from intense sexual selection pressure.

• Mating Systems and Sexual Selection

  • In mating, there are two types of selection (intersexual, intrasexual) and three mating systems (monogamous, polygynous, polyandrous).
  • Not all animals reproduce sexually, but many that do have the same challenge: they need to find a suitable mate and often have to compete with other individuals to obtain one.
  • Two types of selection that occur during the process of choosing a mate may be involved in the evolution of reproductive traits called secondary sexual characteristics.
  • These types are: intersexual selection (the choice of a mate where individuals of one sex choose mates of the other sex) and intrasexual selection (the competition for mates between species members of the same sex).
  • An example of intersexual selection is when female peacocks choose to mate with the male with the brightest plumage .

• Natural Selection and Adaptive Evolution

  • Natural selection drives adaptive evolution by selecting for and increasing the occurrence of beneficial traits in a population.
  • Natural selection only acts on the population's heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency.
  • Natural selection does not act on individual alleles, however, but on entire organisms.
  • Natural selection acts at the level of the individual; it selects for individuals with greater contributions to the gene pool of the next generation, known as an organism's evolutionary fitness (or Darwinian fitness).
  • Through natural selection, a population of finches evolved into three separate species by adapting to several difference selection pressures.

• Methods of Reproducing

  • Animal reproduction is essential to the survival of a species; it can occur through either asexual or sexual means.
  • The known methods of reproduction are broadly grouped into two main types: sexual and asexual.
  • Many organisms can reproduce sexually as well as asexually.
  • Sexual reproduction ensures a mixing of the gene pool of the species.
  • The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur.

• Biological Influences on Sexual Motivation

  • Sexual motivation, often referred to as libido, is a person's overall sexual drive or desire for sexual activity.
  • Based on the pleasure model of sexual motivation, the increased sexual pleasure that occurs following oxytocin release may encourage motivation to engage in future sexual activities.
  • Studies have suggested that humans might use odor cues associated with the immune system in order to select mates.
  • Sexual motivation can be measured using a variety of different techniques, including self-report measures such as the Sexual Desire Inventory.
  • Sexual motivation can also be implicitly examined through frequency of sexual behavior.

• Advantages and Disadvantages of Sexual Reproduction

  • The fact that most eukaryotes reproduce sexually is evidence of its evolutionary success.
  • Scientists recognize some real disadvantages to sexual reproduction.
  • In sexual populations, the males are not producing the offspring themselves.
  • Why is sexuality (and meiosis) so common?
  • As one species gains an advantage, this increases selection on the other species; they must also develop an advantage or they will be out-competed.

• Processes and Patterns of Evolution

  • Natural selection can only occur in the presence of genetic variation; environmental conditions determine which traits are selected.
  • Genetic diversity within a population comes from two main mechanisms: mutation and sexual reproduction.
  • Sexual reproduction also leads to genetic diversity: when two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and thus phenotypes in each of the offspring.
  • However, sexual reproduction can not lead to new genes, but rather provides a new combination of genes in a given individual.
  • Explain why only heritable variation can be acted upon by natural selection

• Mate Selection

  • There is wide cross-cultural variation in the social rules governing the selection of a partner for marriage.
  • There is wide cross-cultural variation in the social rules that govern the selection of marriage partners.
  • In some of these societies, individuals are only allowed to select partners from the individual's social group.
  • In other societies, on the other hand, partners can be selected from a different social group than one's own.
  • This practice occasionally exists to conceal an elopement, but it also occasionally represents sexual violence.

• Genetic Variation

  • Genetic variation is essential for natural selection because natural selection can only increase or decrease frequency of alleles that already exist in the population.
  • Because natural selection acts directly only on phenotypes, more genetic variation within a population usually enables more phenotypic variation.
  • Neutral alleles are neither selected for nor against and usually remain in the population.
  • However, existing genes can be arranged in new ways from chromosomal crossing over and recombination in sexual reproduction.
  • Overall, the main sources of genetic variation are the formation of new alleles, the altering of gene number or position, rapid reproduction, and sexual reproduction.

• Social Context and Sexual Behavior

  • Social context influences sexual behavior; sexuality is expressed and understood through socialized processes.
  • Sexual behavior refers to the manner in which humans experience and express their sexuality.
  • Human sexual activity has sociological, cognitive, emotional, behavioral and biological elements, including physiological processes such as the reproductive mechanism, the sex drive and pathology; sexual intercourse and sexual behavior in all its forms; and personal bonding and shared emotions during sexual activity.
  • Since sexuality is expressed through means learned by socialization, social context is bound to influence sexual behavior.
  • For example, sexual activity with a person below some age of consent and sexual assault in general are criminal offenses in most jurisdictions.