The right signal can even bring about the unexpected resurrection of organs long buried by evolution. Birds don’t have teeth, but their dinosaur ancestors certainly did. If a piece of ectoderm from a foetal chicken’s beak is grafted onto a piece of mesoderm from a foetal mouse’s mandible, and both are placed in the eye-orbit of a young mouse, the chicken tissue, which has not seen a tooth for sixty million years, suddenly begins to make them: hen’s teeth, shaped something like tiny molars, complete with dentine and enamel. This implies that the molecular signals used by Tyrannosaurus rex to make its mighty fangs are the same that a mouse uses to make its miniature molars. Signals that chickens just seem to have lost.
Perhaps it is also the retrieval of an ancient signalling system, partly buried by evolution, that causes some people to have extra nipples or even breasts. Humans and great apes have only two nipples but most mammals have many more. Sometimes extra nipples are little more than a small dark bump somewhere on the abdomen; at other times they are fully developed breasts. They are common: between 2 and 10 per cent of the population have at least one. In Europeans extra nipples or breasts are usually found somewhere below the normal ones, often in a line running directly down the abdomen. Japanese women, curiously, seem to get them above the normal breasts, often in the armpits.
These patterns of extra nipples may recollect an ancient ‘milk line’ – a row of ten pairs of teats that ran from the armpits to the thighs in some ancestral mammal. Armpit breasts are found in the lemur, Gaelopithecus volans, and the record number of nipples found on a single person seems to be nine (five on one side, four on the other). Wherever they are, extra breasts often work like normal ones, swelling and even lactating during pregnancy, and there are even accounts of women suckling children from supernumerary thigh-breasts. Extra nipples and breasts run in families, though the mutation (or mutations) that causes them has not been identified. However, a group of London researchers are attempting to determine the mutation behind a strain of mice that have eight nipples instead of the usual six. They have already dubbed the gene Scaramanga – for the villain of the James Bond film The Man with the Golden Gun who had, as a mark of his depravity, a supernumerary nipple on his upper left chest.
ARTEMIS EPHESIA
Breasts bring us back to Linnaeus. In 1761, made famous by Systema naturae, Linnaeus published one of his lesser-known works, a synopsis of the Swedish animals called Fauna svecica. The name was revolutionary: it was the first time that the word ‘fauna’ – from the Roman name for Pan-the-God – had been used to describe a work of this sort; a direct counterpart to the ‘floras’ that were already proliferating. As a frontispiece to this work Linnaeus chose a curious emblem, a representation of the Greek goddess Artemis, or Diana, of Ephesus. We don’t know why he picked this particular emblem, but there are several possibilities.
Artemis Ephesia was, in the inexplicably duplicitous way of Greek deities, goddess of both nature and cities. In her original incarnation as the object of a cult that flourished in Asia Minor from around the sixth century BC, her image was hung on city walls to protect them from evil, while being surrounded by icons of the country: garlands of vines and climbing animals such as lions, snakes, birds and harpies. Retrieved from the ruins of Ephesus, the eighteenth century made her into a symbol of wild-ness and of reason. The Jacobins even dedicated a Temple of Reason to her that once stood in Strasbourg, but is now gone. Perhaps this is why Linnaeus placed her at the front of his Fauna – as a symbol of the mastery of Reason over Nature, albeit a Swedish nature, in which, far from her Mediterranean home, Artemis stands among browsing reindeer.
But perhaps she had another, more direct, meaning for Linnaeus as well. What is most striking about his Artemis are not the animals that surround her, but her four prominent breasts. In this she is a direct echo of the statues of her in antiquity, all of which are laden with a varying number of thoracic and abdominal protuberances. In the Renaissance these bumps were invariably interpreted as a case of extreme polymastia, but more sceptical modern scholars say they are more likely to have simply been strings of dates, bulls’ testicles, or perhaps just part of the cuirass in which the goddess was clad. Be that as it may, Linnaeus’ Artemis obviously has four fine breasts, and it seems quite possible that they are a direct allusion to one of his finest inventions, the Mammalia. For Linnaeus made the presence of mammary glands one of the defining features of what we are: members of that great class of creatures that embraces simultaneously the pygmy shrew and the blue whale.
There is a third possible source of Linnaeus’ Artemis, one that brings us back to where we started – the way in which we differentiate ourselves from the rest of brute creation. When describing a species, Linnaeus did what taxonomists still do – he listed the things that distinguish it from all others. For all species, that is, but one: our own. When it came to Homo sapiens, instead of speaking of the number and kinds of teeth we have, the density of our hair, the distribution of our nipples, Linnaeus wrote only this: Nosce te ipsum. In a footnote he says that these are the words of Solon written in letters of gold upon the temple of Diana. Perhaps in choosing Artemis Ephesia as his icono-graphic symbol, Linnaeus is remembering and alluding to this account of the human species, the most concise possible: know thyself.
That is where Linnaeus’ discussion of Homo sapiens ends, but for a few strangely exigent epigrams in which he instructs us in the meaning of the new identity that he has given us. ‘Know thyself,’ he says, created by God; blessed with minds with which to worship Him; as the most perfect and wonderful of machines; as masters of the animals; as the lords of creation – all sentiments that today ring with the poignancy of certainties long since gone. Yet it is his parting shot that is most telling, and that could be taken as epigrammatic of much of what I have written here:
Know thyself, pathologically, what a fragile bubble you are, and exposed to a thousand calamities.
If you understand these things, you are man, and a genus very distinct from all the others.
IX
THE SOBER LIFE
[ON AGEING]
HUNTINGTON DISEASE is one of the nastier neurodegenerative syndromes. It usually first appears as a mild psychosis and does not seem especially serious. But, as the disease progresses, the psychotic episodes increase in frequency and severity. Motor-coordination also deteriorates, a characteristic rigidity of gait and movement sets in and then, eventually, paralysis. In the disorder’s final phase, which can take up to ten or twenty years to appear, the patient becomes demented and experiences neural seizures, one of which is eventually fatal. The disease is caused by dominant mutations that disable a protein used in synaptic connections of the brain’s neurons. For reasons that are not fully understood, the mutant form of the protein initiates a molecular programme that gradually kills the neurons instead.