9.3 natural selection

what is evolution

is is the gradual change in the characteristics of a species

what was Darwins theory of natural selection based on

variation

birthrate

natures balance

variation

noted all members of a species vary

birth rate

realised all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase.

nature balance

although the birth rate of organisms was very high, each numbers tended to remain at a relatively constant level

what interpretations were made from the observations

because of excessive birth rate and limited resources - there must be a struggle for existence

survival of the fittest - organisms with favourable characteristics survived.

what is a selective agent

an environmental factor that influences which traits within a population are more likely to be passed on to the next generation.

what are the principles of evolution through natural selection