Having discussed how difficult it is to define ‘species’ in my last post, I feel I should stress that biologists still absolutely must use the concept all the time. There is no good in studying an animal, or group of animals, if you don’t name the group to which they belong. Members of a species should always be more closely related to one another that they are to any member of any other species: as an example, doves all look more like each other than they look like a pigeon. This much is objectively true, but the subjective problem lies in where exactly you draw the line.
So doves all look more like each other than they look like pigeons (and vice-versa) but the dove-pigeon grouping all look more like each other than they look like crows (and vice-versa). Are doves and pigeons and crows three distinct species or are dovepigeons and crows two distinct species and doves and pigeons are subspecies of dovepigeons? The more species you add, and the deeper back in time their genetic split goes, the more complex this gets.
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