Which theory states that living things change lower overtime in response to changes their environment

Natural selection is the theory

Darwin's theory

Explanation:

Species change over time; some traits become more common, others

less. This process of change is driven by natural selection. The traits that become more common are the ones that are "adaptive" or "increase fitness"

(that is, a creature's chances of living longer and producing more offspring).

Example: the long neck of giraffes.