The test for whether things were the same species used to be, can they produce *fertile* offspring — hence, a mule is sterile, as are lion-tiger hybrids, and their parents are two different species. That also works to an extent in botany, as it is possible to produce stable hybrids that are not sterile but won’t produce their own kind.
My view on humans is, the use of the term species is an incorrect convention, but that it will pass away as more and more reliance is placed on genetic studies, and morphological divisions lose their importance in the understanding of our ancestors. :’)
Thanks.