Individuals of a species vary. Some variation is continuous, such as height, which can take any value in a range. Some is discontinuous, such as blood group, which falls into separate categories. Variation can be caused by genes, by the environment, or by both.
Natural selection explains how species change over time. Organisms produce more offspring than can survive. Those with variations that suit their environment are more likely to survive and reproduce, passing on their useful alleles. Over many generations the population changes; this is evolution. Peppered moths in polluted areas became mostly dark, because pale moths were easier for birds to spot on sooty trees. Humans also cause change by selective breeding, choosing which animals or plants breed.
Worked example
Why did more dark peppered moths survive near sooty factories?
- Tree bark was dark with soot.
- Dark moths were camouflaged, so birds ate fewer of them.
Answer:They survived to breed and passed on the dark allele.
Key words
- natural selection
- better-suited individuals survive and breed more
- evolution
- change in a species over many generations
- continuous variation
- can take any value in a range
- selective breeding
- humans choosing parents with useful features
New questions every time.
NGSS-referenced: MS-LS4-4