natural selection
Adaptation of organisms to the environment by competitionAnt. artificial selection, e.g. breeding dogs
Mechanism:
- Variation
- Phenotypic variation: individuals of a population vary.
- Genetic variation: some of the differences are inheritable.
- <= mutation
- Overproduction: species tend to produce more offsprings than can survive.
- Competition: individuals must compete for limited resources.
- Food
- Territory
- Mate
- Differential success: the fittest survives and reproduces.
[!abstract] fitness
Ability to survive and to reproduce
Types
Directional selection
Trait evolves towards one extreme
[!example] Evolution of horse towards larger size and one toe
[!example] Industrial melanization of moths
Environment becomes darker => moths become darker
Disruptive selection
Trait evolves towards both extremes
[!example] Adaptive radiation
[!example] Batesian mimicry
Mimicry where a harmless species mimics the warning signals of a toxic species
[!example] Evolution of seedcracker birds towards two beak sizes
Stabilizing selection
Trait evolves towards the center
[!example]+ Sickle cell disease
Homozygous dominant: suffers from sickle cell
Homozygous recessive: suffers from malaria
Heterozygous: protected from both
=> evolution of humans in malaria regions to be heterozygous[!abstract] Heterozygote advantage
Genetic advantage of being heterozygous for a specific trait
Ajitani Hifumi