So what is a species anyway? A primatological perspective

Since Darwin's time, the question “what a species” has provoked fierce disputes and a tremendous number of publications, from short opinion papers to thick volumes.1 The debates covered fundamental philosophical questions, such as: Do species exist at all independently of a human observer or are they just a construct of the human mind to categorize nature's organismic diversity and serve as a semantic tool in human communication about biodiversity?2–4 or: Are species natural kinds (classes) or individuals that are “born” by speciation, change in course of time, and finally “die” when they go extinct or diverge into new species?5–8 Also included was the problem of species as taxa (taxonomic) versus species as products of the speciation process (evolutionary).9 More pragmatic issues arose, such as: How can we reliably delineate and delimitate species?10, 11 The great interest in what a species is reflects the importance of “species” as fundamental units in most fields of biology, especially evolutionary biology, ecology, and conservation.2, 12–14