Introduction
So what is taxonomy?
Taxonomy is the way we order and classify the natural world. It is more of a specialised field than many people realise. Concepts like “how different does it have to be to be a distinct species/genus/family?” are not relevant; what we want to know is information about evolution and phylogeny.
The basic unit of taxonomy is the species. Species have a real existence: they are evolutionary lineages (de Queiroz, 2007). What we seek is evidence for these lineages, and the way to recognise them is what has been called the Phylogenetic Species Concept (Groves, 2001; Cotterill et al., 2014) which, following de Queiroz's (2007) analysis, would be better dubbed the Diagnosability Criterion. If one population (or group of populations) is consistently (diagnosably) different from others in heritable characters, this is absolute evidence that it forms a separate evolutionary lineage. The proposal that a given population, sample, cluster, or whatever, constitutes a species is therefore a testable hypothesis.
The so-called Higher Categories do not, on the other hand, have a real existence. Since Hennig (1950/1966) there has arisen a general consensus that a genus or a family must be monophyletic, but beyond that there is subjectivity. There has been a proposal to link these categories to time-depths (see, for example, Groves, 2001); thus, a genus should have been separated around the Miocene–Pliocene boundary, and a family should have been separated around the Oligocene–Miocene boundary. There has been surprisingly little discussion about this, which is distressing, because we are supposed to be doing science, and science is about testability.
The concept of Cheirogaleidae
Early zoologists took a while to recognise that dwarf and mouse lemurs are related to each other, rather than, for example, mouse lemurs being Madagascan galagos. More modern arrangements were beginning to be expressed by the mid-1800s. In Gray (1870), the genus Cheirogaleus was included in the Lemuridae, and two years later Gray (1872) recognised a tribe Cheirogaleina with more or less its present composition.