As I've stated in my comment there are more than enough examples where that definition of species is lacking - it's not a line/plane/SVM-hyperplane.

Evolution is gradual, there are no big species jumps.

What was there between sapiens and erectus, X? What was between sapiens and X, and X and erectus, Y and Z?

What was then between sapiens and Y, Y and X, X and Z, Z and erectus?

This can go on forever, evolution is by nature gradual, lets say it in your terms, a regression is more suitable than classification.

What point in this finely continous line do we pick for discrimination? Speciesism discovered!