Compare monophyletic and paraphyletic . In evolution , the process through which a group of species diverge from a single ancestral form. People with this trait may suffer milder symptoms of sickle-cell anemia, or may have no symptoms. Some scientists believe the trait actually provides an evolutionary advantage in tropical environments because the slightly altered shape of the blood cells causes a person to be more resistant to malaria . The species is the most fundamental unit of evolution and is the most specific taxonomic level.
Spontaneous mutations arise at a remarkably constant rate.
The origin of animal life on the planet. The origin and evolution of a particular animal species.