IS THAT A NEW ONE?

I remember when I was reading for my first degree many years ago that one early lecture on ecology directed us to the difficulty in determining just what a species is. All the students thought they knew until we were asked to write down a definition that would hold secure against probing questions by our lecturer. Then all kinds of problems arose, such as cloning, parthenogenesis and hybridisation. Even Charles Darwin noted that it was trying to define the undefinable. In my cohort of students and the lecturer, I recall we came up with something between twenty and thirty different possible definitions!

Humans love to classify and impose order on the world but it is of course an artifice, albeit a very useful, even fundamental, way of getting to grips with the bewildering numbers and complexity of all the living organisms on our planet. Taxonomy, i.e. classifying and naming things, is a huge and dynamic subject. Perhaps the commonest non-specialist definition of a species is an organism that can breed with others of its kind and produce fertile offspring. This has recently been made all the more intricate, and often counter-intuitive, because of the advances in DNA analysis and the ability to define whole genomes. Taking a genetic approach suggests that every species would have a distinct set of genes or genetic profile. That would mean many more species than we thought. Then that, too, becomes complicated when genetic variations due to environmental or geographical variations are considered. Another approach is cladistics where a species could be considered as a clade; in other words all those descended from a common ancestor.