- process in which individuals best suited in the environment survive and reproduce naturally to produce their phenotype offsprings.
- selection pressure is exerted by environmental factors eg presence of light and nutrients may affect the survival of plant organism in a given area.
- it results in competition for light and nutrients.
- the best adapted organism only survive to reproduce whilst other organisms die.
The role of natural selection in evolution.
- individuals in population have great reproductive potential;
- in population remain roughly constant ;
- many fail to survive / die ;
- do not reproduce ;
- due to environmental factors / named factor ;
- variation in members of population ;
- those best adapted survive ;
- reproduce / pass on alleles ; R genes
- genetic variation leads to change in phenotype ;
- ref: changes in gene pool ;
- over time produces evolutionary change ;
- new species arise from existing ones
Why variation is important in natural selection.
- ref. continuous / discontinuous variation ;
- genetic / inherited variation ;
- variation in phenotype / characteristics ;
- (can be due to) interaction of genotype and environment ;
- e.g. of characteristic that influences survival ;
- ref. intraspecific competition / struggle for existence ;
- those with favourable characteristics survive / AW ;
- pass on favourable characteristics to offspring ;
- those with disadvantageous characteristics die ;
How natural selection may bring about evolution.
- individuals in population have great reproductive potential ;
- numbers in population remain roughly constant ;
- variation in members of population ;
- environmental factors / named factor (biotic or abiotic) ;
- (cause) many, fail to survive / die / do not reproduce ;
- those best adapted survive / survival of the fittest ;
- (reproduce to) pass on alleles ; R genes
- genetic variation leads to change in phenotype ;
- ref: changes in, gene pool / allele frequency ;
- over time produces evolutionary change ;
- new species arise from existing ones / speciation ;
- directional / stabilizing, selection ;
Diffenceres between natural and artificial selection
Artificial selection | natural selection |
---|---|
Selection pressure applied is by humans | Environmental selection pressure |
Genetic diversity is lowered | Genetic diversity remains high |
Inbreeding is common | Outbreeding is common |
inbreeding depression | less inbreeding depression |
Increased homozygosity | Decreased homozygosity |
Usually faster | Usually slower |
Not for survival/evolution | Promotes survival/evolution |
No isolation mechanisms operating | Isolation mechanisms do operate |