Last week Daedalus pointed out that a fetus in the womb will accept foreign tissue as part of itself, and will continue to accept that tissue in adulthood. So, he says, the way is open to creating mixed species — centaurs, griffins, sphinxes, unicorns and so on. To make a unicorn, for example, add a few rhinoceros cells to a horse fetus. The adult horse will then accept a rhino horn transplant. But surgery would probably work better on the fetuses. Fetal rhinoceros horn-bud tissue would be grafted onto the forehead of the fetal horse in utero. The growing fetus, with its greater capacity for repair and development, would probably solve the various compatibility problems better than a team of surgeons trying to marry up the inflexible adult tissues.

Biologists, not to mention owners of zoos, leisure parks and nature reserves, would be fascinated by the resulting chimaerae. Even the classical chimaera — part lion, part goat, and part snake — might be feasible. It would probably not breed true, or even at all, but would still be a biological triumph. Yet Daedalus has a more challenging goal — animal–plant chimaerae. Imagine, he says, a combined man and green plant. The plant would photosynthesize, taking in carbon dioxide and producing oxygen and glucose; the man would conduct the reverse reaction. He would also produce urea and other metabolites useful to the plant — which would thus act as an extra liver and kidney. Such a chimaera would be a most efficient self-contained ecosystem.

The problems are formidable. Even with immunocompatibility guaranteed, few plants could be genetically engineered to have a sap compatible with, or replaceable by, human blood. Even Daedalus is unlikely to create a man with real cauliflower ears. But a man with algae growing happily in his skin should be far more feasible. He would absorb sunlight, and feed, breathe and excrete internally, at least to a useful degree. The first ‘little green men’ will worry the flying-saucer cultists, and could arouse novel colour prejudice. But, with their wonderful ecological economy, they may be the way forward for humanity. Besides, with a little cunning plant-metabolic transfer, they could enjoy a constant internal supply of nicotine, caffeine, cocaine or cannabinoids.

The further Inventions of Daedalus (Oxford University Press), 148 past Daedalus columns expanded and illustrated, is now on sale. Special Nature offer: m.curtis@nature.com