Elements of Natural Selection Flashcards Preview

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Flashcards in Elements of Natural Selection Deck (11):

What is Evolution?

Evolution is the variability in the frequency of heritable traits that appear in one generation to the next.


What is Natural Selection?

* Natural Selection, commonly referred to as "survival of the fittest" is the driving force of evolution.
* Natural Selection favors traits that increase an organism's chances of survival and acts against traits that hinder its survival.



Adaptations are inherited traits that help populations better adapt to their environment and therefore increase their chances of leaving behind offspring.


Stabilizing Selection

Stabilizing selection selects AGAINST traits that are UNCOMMON within the population. It favors the most common traits within the population, therefore individuals with the common traits within the population are better adapted to the environment.


Directional Selection

Directional selection favors one extreme in a range of traits. If directional selection persists over generations, the favored traits will become more extreme, leading to a distinct change in the allele frequencies within a population.


Insecticide Resistance

* Insecticide resistance is a result of Directional Selection.

* Since there are a variety of traits in a population, some individuals have stronger resistance compared to others. Over many generations however, the majority of the surviving offspring will be resistant to insecticide.

* This is concerning because the response to such resistance by insects is to use a stronger insecticide which may prove harmful to the environment.


Disruptive (or Diversifying) Selection

Disruptive selection occurs when the environment favors an extreme in a range of traits while also selecting against the more common traits.


Sexual Selection

Sexual selection is the differential mating of males (sometimes females) in a population. FEMALES increase the QUALITY of their offspring by choosing to mate with superior males. Males try to increase their success in mating by maximizing the quantity of offspring produced.


Sexual Dimorphism

Sexual dimorphism is the differences in the appearance of male and females. For example, male peacocks tend to have more brightly colored plumage than females.


Artificial Selection

Artificial selection is a form of directional selection carried out by humans. Therefore, artificial selection is NOT NATURAL.



In order for natural selection to operate, there must be variation among individuals in a population. Mutations provide the raw material for new variation by inventing alleles that never before existed in the gene pool.