According to Darwin's theory of evolution, differences between species may be the result of:
A. mutagenic agents.
B. natural selection.
C. the disuse of body structures.
D. the transmission of acquired characteristics.
Natural selection means that nature determines what traits are favorable and it is those traits that get passed on to offspring and increase. Disuse of body structures and acquired characteristics are characteristic of LaMarcks theory of evolution, which has been disproved. Mutagenic agents increase the rate variation but Darwin did not understand about mutations when developing his theory.