These are physical features shared by organisms with common ancestry; they may have the same structure, but different functions developmentally mature organisms.

Homologous structures

Homologous structures are physical features that can be found in very different animals, indicating that the organisms seem to be related or descent from a common ancestor. Homologous structures may have similar functions or form in different organisms. An example is the human eyes which are homologous to the eye bulbs located on the heads of blind creatures that reside in caves.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.