 To better understand this third option it is useful to see more precisely what is being doubted. Biologists make a distinction between the species category and species taxa. Species taxa are the individual lineages we call ‘species.’ Homo sapiens and Canis familiaris are species taxa. The species category is a more inclusive entity. The species category is the class of all species taxa. The third option does not call into question the existence of Homo sapiens or Canis familiaris or any other lineage that we call ‘species.’ The third option just calls into question the existence of the categorical rank of species. (For different approaches that call into question the existence of the species category, see Mishler and Wilkins 2018, and Haber 2019. For recent defences of the reality of the species category see Currie 2016, Barker 2019a, Novak and Doolittle 2021.)