The Neanderthal are usually classified as a different species, yet they could interbreed with homo sapiens.
The convention of calling Neanderthals a different species arose before anybody knew they could interbreed with Cro Magnons, and persists by inertia. Interbreeding was only demonstrated in 2010. It typically takes longer than that for scientists to change their ways, same as regular folks. By normal biological naming criteria, Neanderthals were a human subspecies.
(Also, interbreeding in the wild and producing fertile offspring is not an all-or-nothing matter. All species start out as subspecies; as they gradually drift apart, the probability of interbreeding and the probability of the offspring being fertile gradually decline. So it's entirely possible that 98% of Neanderthal/Cro Magnon crosses were infertile and the observation of Neanderthal genes in modern humans merely reflects our descent from the exceptional 2%. If and when that turns out to be the case, nobody will bat an eye at classifying them as a separate species; but we don't currently have reason to think that's what happened. This is a very hard thing to determine, for obvious reasons. Let us all remain open-minded on this point.
So by all means, feel free to supply evidence that Indonesian/Dutch hybrids are usually infertile and Wolfgang is a freak of nature.
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Besides, you are begging the question by assuming that ability to interbreed denotes the same species. Even if it did for lower life forms, such a convenient globalist definition should not apply to humans, who must not be classified under the same rules that animals are, any more than animals should be classified with plants.
Classification rules for animals are different from those for plants because (a) botanists and zoologists are culturally different groups of people with little influence on each other, and (b) animals don't reproduce by cuttings. That anthropologists are culturally different from zoologists isn't a good reason to use a different species definition.