In the origin of species, darwin argued that the mechanism of descent with modification was in the origin of species, darwin argued that the mechanism of descent with modification was artificial selection uniformitarianism natural selection inheritance of acquired characteristics

Natural selection

Explanation:

According to Darwin, natural selection is the mechanism through which evolution takes place. Natural selection is the mechanism through which the heritable traits characteristic changes in an organism over the generations. Variations in traits of organisms are passed down through the generations and each generation has their genes affected by the environment.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.