Darwin's theory of evolution by natural selection states that individuals in a population show variation; there is competition for resources; individuals with characteristics best suited to the environment are more likely to survive and breed; and they pass on their alleles, so these become more common over many generations. If populations are separated and change enough that they can no longer interbreed, a new species forms.
Evidence for evolution includes fossils showing gradual change, antibiotic resistance in bacteria evolving quickly, and DNA comparisons showing how closely species are related. Linnaeus grouped organisms into kingdom, phylum, class, order, family, genus and species, and named each with a binomial such as Homo sapiens. Today the three-domain system uses genetic evidence: Archaea, Bacteria and Eukaryota.
Worked example
How can a species of insect become resistant to a pesticide?
- A few insects have a mutation that lets them survive the pesticide.
- They survive and breed while others die.
Answer:Their offspring inherit the allele, so over generations most of the population is resistant.
Key words
- natural selection
- better-adapted individuals survive and breed more
- speciation
- the formation of a new species
- binomial name
- genus + species, e.g. Homo sapiens
- extinction
- no individuals of a species remain
New questions every time.
NGSS-referenced: HS-LS4-2