A species is a group of individuals which are:
1. Morphologically alike
2. Capable of interbreeding to produce viable and fertile offspring.
3. Able to demonstrate a limited flow of genes between species.
There are two ways species can develop...
This is where the evolution of a species is linear, and gradually changes from one species to another.
This is where a multiple of species develop from one. This process is sometimes referred to as divergent evolution or speciation.