Emeritus Professor of the Public Understanding of Science, University of Oxford; Author, The God Delusion
BREAKING THE SPECIES BARRIER
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.
Theoretically we understand this. But what would change everything is a practical demonstration, such as one of the following:
1. The discovery of relict populations of extinct hominins such Homo erectus and Australopithecus. Yeti-enthusiasts notwithstanding, I don't think this is going to happen. The world is now too well explored for us to have overlooked a large, savannah-dwelling primate. Even Homo floresiensis has been extinct 17,000 years. But if it did happen, it would change everything.
2. A successful hybridization 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.
3. An experimental chimera in an embryology lab, consisting of approximately equal numbers of human and chimpanzee cells. Chimeras of human and mouse cells are now constructed in the laboratory as a matter of course, but they don't survive to term. Incidentally, another example of our speciesist ethics is the fuss now made about mouse embryos containing some proportion of human cells. "How human must a chimera be before more stringent research rules should kick in?" So far, the question is merely theological, since the chimeras don't come anywhere near being born, and there is nothing resembling a human brain. But, to venture off down the slippery slope so beloved of ethicists, what if we were to fashion a chimera of 50% human and 50% chimpanzee cells and grow it to adulthood? That would change everything. Maybe it will?
4. The human genome and the chimpanzee genome are now known in full. Intermediate genomes of varying proportions can be interpolated on paper. Moving from paper to flesh and blood would require embryological technologies that will probably come on stream during the lifetime of some of my readers. I think it will be done, and an approximate reconstruction of the common ancestor of ourselves and chimpanzees will be brought to life. The intermediate genome between this reconstituted 'ancestor' and modern humans would, if implanted in an embryo, grow into something like a reborn Australopithecus: Lucy the Second. And that would (dare I say will?) change everything.
I have laid out four possibilities that would, if realised, change everything. I have not said that I hope any of them will be realised. That would require further thought. But I will admit to a frisson of enjoyment whenever we are forced to question the hitherto unquestioned.