Sequential Chimeras

Abstract

The name “chimera”, or its ancient Greek equivalent, was originally applied to a fabulous, fire-spouting monster, with a lion’s head, a she-goat’s body and a serpent’s tail. Most of our information on it comes from Homer, but I have not consulted the original. He seems to have been quite definite that the goat-portion was female, but I do not know whether he specified the sex of the head and tail portions. Whatever the answer to these intriguing problems, this seems to be the first use of the term, so I shall regard it as “definition 1”. The same term, chimera, has been applied in more recent years to experimentally produced organisms made up of tissues of two species or of two genetically distinct strains of the same species, by techniques ranging from simple grafting to various forms of genetic engineering. This gives us “definition 2” of chimera. Modern experimental biologists have produced nothing like the creature described by Homer, but their chimeras, like his, simultaneously show identifiable features of different origin. I should now like my readers to consider the possibility, and indeed the strong probability, that organisms with identifiable features of different origin existed long before there were genetic engineers or ancient Greeks, for I maintain that such organisms have been produced naturally, at intervals, throughout much of evolutionary time and that a great many natural animals are really chimeras.