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| Taxonomic categories |
The species is the basic
taxonomic category used by biologists to classify living things. The other
categories (genus, family, order, class and phylum)
are considered artificial and arbitrary. On the other hand, we tend to regard the
species as natural, obvious, similar to a concept when the represented objects
are living beings. But we will not enter here into the famous problem of universals, nor wonder
on whether concepts (and species) really exist or are mere constructs of the
human mind.
The classic definition of a species
is: a set of living beings that share common characteristics and can
interbreed, giving rise to fertile offspring. Notice that the
use of the word interbreed implies that the living
things in question use sexual reproduction. This leads us to ask whether the
concept of a species should be restricted to living beings with this type of
reproduction, or it can be extended to those that reproduce otherwise, such as prokaryotes
and some eukaryotes. This question can be answered in several ways:
