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Friday, March 19, 2010

Evolution and Genes -3

Evolutionary Psychology

Evolutionary psychology uses evolutionary theory to explain similarities in psychological characteristics. According to evolutionary psychologists, patterns of behavior have evolved through natural selection, in the same way that physical characteristics have evolved. Because of natural selection, adaptive behaviors, or behaviors that increase reproductive success, are kept and passed on from one generation to the next.

Mating Behavior

Because reproductive success is such a hot topic in evolutionary theory, evolutionary psychologists often choose to study mating behavior. Researchers such as Robert Trivers have proposed that mating strategies depend on the amount of parental investment made by males and females of a species. Parental investment refers to all the resources spent to produce and raise offspring. In many species, males and females don’t make equal parental investments. The sex that invests less competes with others of its sex to mate with the sex that invests more. The sex that invests more in parenting tends to discriminate more when selecting a mate.
Sexual Selection
Usually, the female of the species invests more in parenting. Females of many species choose their mates based on certain characteristics, such as large canine teeth in a male baboon or flashy tail feathers on a peacock, which in turn means those traits will be passed on to their male offspring. Biologists call this process sexual selection, which is related to natural selection. Whereas natural selection results in adaptations that make organisms more likely to survive, sexual selection just makes them more likely to mate. Sometimes the adaptations that are a result of sexual selection, such as flashy tail feathers, are not actually much help in terms of survival.
A situation called polygyny arises when a single male mates with many different females. Polygyny tends to occur in certain animal species, notably those in which females invest more in parenting than males. In a polygynous mating system, males compete with other males in order to get access to females. Females tend to pick the winners of such competitions. Picking winners helps to ensure that their offspring will have good genes.
Example: Mountain gorillas are polygynous. The females and children live in groups defended by a mature male, with whom they mate. If they choose, however, females may select a stronger, more desirable mate. In such a case, the hopeful suitor would challenge the dominant male and the females would choose the winner.

Problems with Evolutionary Explanations

Scientists have used evolutionary theory to explain human behavior patterns, such as a female tendency toward monogamy and a male tendency toward promiscuity. However, other researchers argue that such explanations don’t apply well to humans, because the theories stem from stereotypes. Humans behave in complex and variable ways, and factors such as culture strongly influence this behavior. Furthermore, it is difficult to tie variation in behavior to variation in reproductive success. Evolutionary explanations also raise controversy because people can use them to support various social and political agendas.
Some researchers criticize evolutionary explanations because anyone can work backward from an observation to develop an evolutionary explanation. These psychologists point out that the fact that a trait exists does not necessarily mean that trait is adaptive. The trait may have been helpful earlier in our human history but did not remain adaptive, or the trait could be a side effect of another adaptive trait.

Quick Review

Principles of Genetics

  • Behavior geneticists study the genetic basis of behavior and personality differences among people.
  • The more closely people are biologically related, the more genes they share.
  • Traits can be monogenic (determined by one gene) or polygenic (determined by several genes).
  • Researchers use heritability to determine how much of a trait’s variation within a population is due to genes.

Types of Genetic Studies

  • Psychologists use family studies, twin studies, and adoption studies to see whether, and to what extent, characteristics are genetic.
  • Heredity interacts with environment to influence psychological traits.

Evolution and Natural Selection

  • Evolution is the change in the frequency of genes in a population.
  • Charles Darwin proposed the theory of natural selection, which states that inherited characteristics that give an organism a survival or reproductive advantage are passed on more often to future generations than other inherited characteristics.
  • An adaptation is an inherited characteristic that increases in a population because it provides a survival or reproductive advantage.
  • Inclusive fitness is the reproductive fitness of an individual organism plus any effect that the organism has on increasing reproductive fitness in related organisms.
  • Evolution relies on mutations, or small changes in genes.

Evolutionary Psychology

  • Evolutionary psychologists use evolutionary theory to explain patterns in psychological characteristics.
  • Researchers study mating behavior to investigate aspects of evolutionary psychology.
  • Parental investment refers to all the resources spent to produce and raise offspring.
  • Sexual selection refers to the tendency of females to choose mates based on certain characteristics, which are then passed on to their male offspring.

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