2.5 Variation and Natural Selection 🦍

Variation

Small differences/ variations in the same species

Continuous variation

used when there is a gradual change e.g height, mass

Showing continuous variation

histogram which should show normal distribution, most individuals around average

Discontinuous variation

used when there is a limited number of possible values e.g tongue rolling, hand dominance

Showing discontinuous variation

bar chart, has no intermediate values and is in distinct groups

Causes of variation

• Mutations, random changes in number of chromosomes or gene structure

• Reproduction, independent assortment and random fusion of gametes

• Environment, such as diet and health

Natural Selection

1. variation among phenotypes of population

2. organisms compete for resources

3. best adapted individuals survive, less adapted don’t (differential survival)

4. surviving organisms reproduce and pass on beneficial genes to next generation

5. number of best adapted increase

Selective breeding

artificial selection with desirable characteristics which are bred to produce offspring, repeated over generations

Selective breeding in wheat

• shorter stalk length to reduce wind damage

• uniform size, easier to harvest

• larger yield

Evolution (Charles Darwin)

continuing process of natural selection leading to gradual change of organism over time (or new species)

Acceptance of evolution

large timescales make it hard to see happening and some argue it contradicts their religious beliefs

Consequence of evolution

new species better adapted to survive, failure may result in extinction

Fossils

remains of living organisms preserved in rock, evidence of evolution showing how it used to look

Extinction

no living individuals of species left

Endangered

species at risk of becoming extinct

Reasons for extinction

• hunting by humans

• disease

• loss of habitat/ deforestation

• failure to adapt

Preventing extinction

• laws to prevent hunting

• programmes to create nature reserves/ protect habitats

• education to encourage young people