Introduction to Population and Evolutionary Genetics

Speciation

Species - a group of populations through which genes can flow and whose offspring have a fitness equal to the parents

• As evolution progresses, gene flow is eventually stopped between one population and the species as a whole.
• As gene frequencies of a population change, the population may diverge entirely until it is reproductively distinct from other populations of the species. This is called phyletic evolution or anagenesis.

Example: Horseshoe Crabs (see table below)

Geologica Era	Species
Carboniferous	Prestwinchinella rotundala
Permian	Paleolimulus avitus
Jurassic	Limulus walchi
Present	Limulus polyphemus

• Alternatively the population could evolve into two distinct species that exist simultaneously. This is called true speciation or cladogenesis.

Example: Cereal Species