Traditionally, the term species means that one group of critters is different from another group of critters. In the genomic age, it refers to genetic differences - though chimps and humans have 96-99% similarity when comparing the genomes - there is just something that creates those differences we see. 

Similarly, humans were thought to be identical, with some higher power bestowing differences ("that's how God made me"), but now we understand that slight genetic mutations make each individual human different from another, and that together these genetics make up the species - which also shows how easily evolution could branch out to form a new population.

A project pursued to further understand these differences was the 1000 Genomes Project. And guess what...we're all very very different.

 The pilot phase of the project found 15 million gene variants, up to 1% of all human genes, among the 1000 human genomes surveyed (using both low and high accuracy sequencing). Some of these variants make no changes in how a person is put together, others do (like hypertension, diabetes, autoimmune disease, addiction, metabolic disorders, etc), but the amount of variation they found within a small group of the population from the same species is somewhat surprising. It may also explain why finding the genetic mutations associated with disease has been so hit and miss- there are just so many and may not be the same in everyone.

The next step for the project is 2500 genomes.  I'm not lying when I say I am intrigued.

Image: DNA repair, point mutations and genetic variability can occur if DNA breaks or aberrant replication are not repaired