Variation & evolution

Populations show extensive genetic variation. Evolution is a change in the inherited characteristics of a population over time through natural selection: variants with phenotypes best suited to the environment survive and reproduce more, passing on those alleles, and over time a new species may form. Antibiotic resistance in bacteria is a clear example of natural selection.

Variation can be genetic/inherited (from alleles) or environmental (caused by surroundings, e.g. a scar), and many features result from a combination of both.

• Saying organisms "try" or "choose" to adapt (variation arises first; the environment then selects).
• Forgetting antibiotic resistance is natural selection in action.