How Evolution Works

The word evolution means change. The ancient Greeks and Romans studied fossils, compared organisms, and philosophized about how plants and animals originated and survived. Through centuries of refinement, these ideas developed into the current biological definition of evolution as inheritedInherited:
Derived from a preformed genetic code present in an ancestor.
change within a lineageLineage:
Line of descent from an ancestor.
. Over time, these inherited changes give rise to a new species.

By the 1800s, it was generally accepted among geologists and naturalists that the Earth was very old and that the vast diversityDiversity:
The variety of species in a sample, community, or area.
of species on Earth was the product of evolution. The big question, however, was how species evolve. There are now two widely accepted mechanisms for how species evolve: natural selection and genetic drift. Both of these processes are dependent upon variation, both genetic and morphological.