Nature is endlessly inventive! No matter how we try to define the words
"species" and "genus", they are just words. Nature is wordless and
unconstrained by the limitations of human language. The distinctions are
manmade, but they do reflect real differences in nature, and that is why we
retain the words.
 
From one viewpoint, "A species is what a taxonomist says it is." A
taxonomist studying birds, butterflies, cones, or cypraeids will generally
make finer distinctions than a taxonomist studying something unpleasant. A
botanist who liked hawthorns (genus Crataegus) named tens of species in
North America. Hawthorns hybridize readily, and their leaves can have very
diverse shapes on a single tree. Another botanist sent him four leaves
without explaining that all four came from one plant. They were each given
separate, new species names. The botanists still haven't straightened up
the mess, because there really is a large number of hawthorn species and
hybrids.
 
The point to this little tale is that "A species is what a taxonomist says
it is" as long as everyone else agrees with that taxonomist later. When we
read about so many species of hawthorn or cypraeids from one place,
naturally we wonder whether the taxonomist has not allowed his enthusiasm
to color his decisions. But unless we look at the organisms ourselves, we
cannot tell for sure. A person's reputation is based on these decisions, so
most taxonomists manage somehow to keep their enthusiasm in check. Someone
who tends to make fine distinctions is called a "splitter"; a person who
has the opposite tendency is called a "lumper". These are both honorable
terms; most people don't go too far in either direction. And, you know,
sometimes the extreme lumpers or the extreme splitters are RIGHT.
 
Andrew K. Rindsberg
Geological Survey of Alabama