The title of this book is Understanding Species, and I have spoken at length about what we understand species to be and to mean. Now, though, I would like to ruminate for a bit on the ‘understanding’ part.

To understand something is not necessarily to have the One True Answer. Human knowledge, and especially its concepts, is in a state of flux at all times. Sometimes, this is because we are learning new things about what the concept refers to, as is the so-called rule in science (it sometimes isn’t). At other times it is because the concept no longer means anything (like ‘phlogiston’ in chemistry or ‘vital force’ in biology). But sometimes it is because the concept has been included into the ‘what everybody knows’ segment of culture. John Maynard Smith, a famous and influential British evolutionary biologist, called this the Bellman’s Theorem (from Lewis Carroll’s The Hunting of the Snark): ‘what I tell you three times is true’.