Species are somewhat arbitrary, basically at the time of species categorization was it common to think reproduction within this fuzzy group was more common than

Species are somewhat arbitrary, basically at the time of species categorization was it common to think reproduction within this fuzzy group was more common than in some other proposed categorization, or something like that. Probably even less effort was put into it than that in some cases, some people just want to name a "species", no matter how dubious it is. Your definition must not say various sub-Saharan African groups are different species, despite their genetic diversity, or for that matter that there are more than one currently existent Human species, otherwise quite a few people will get mad.