Modern scientists define species purely based on the morphology of a creature whereas the Vedic science delineates species based on the combination of three modes of material nature with the living being. Depending on the combination of material nature and consciousness of the living being, a body is allotted by material nature to the living being.
Modern science purely designates a species based on external features.
Interesting enough modern scientists estimate that there are totally 8.7 million different species on earth, a number very close to the Vedic counterpart (which is 8.4). Anyways, I take the Vedic science as truth as the number will not change, modern estimates change with time which therefore diminishes its value.
The full report can be read here.