"Our ethics and our politics assume, largely without question or serious discussion, that the division between human and 'animal' is absolute. 'Pro-life', to take just one example, is a potent political badge, associated with a gamut of ethical issues such as opposition to abortion and euthanasia. What it really means is pro-human-life. Abortion clinic bombers are not known for their veganism, nor do Roman Catholics show any particular reluctance to have their suffering pets 'put to sleep'. In the minds of many confused people, a single-celled human zygote, which has no nerves and cannot suffer, is infinitely sacred, simply because it is 'human'. No other cells enjoy this exalted status. But such 'essentialism' is deeply un-evolutionary. If there were a heaven in which all the animals who ever lived could frolic, we would find an interbreeding continuum between every species and every other. For example I could interbreed with a female who could interbreed with a male who could ... fill in a few gaps, probably not very many in this case ... who could interbreed with a chimpanzee. We could construct longer, but still unbroken chains of interbreeding individuals to connect a human with a warthog, a kangaroo, a catfish. This is not a matter of speculative conjecture; it necessarily follows from the fact of evolution. A successful hybridisation between a human and a chimpanzee. Even if the hybrid were infertile like a mule, the shock waves that would be sent through society would be salutary. This is why a distinguished biologist described this possibility as the most immoral scientific experiment he could imagine: it would change everything! It cannot be ruled out as impossible, but it would be surprising."