LXXIII
ARISTOTLE’S OWN MODEL of inheritance is a triumph of speculative biology. It is probably one of his most mature theories. It contains his clearest and most detailed account of the mother’s role in reproduction. Here, as nowhere else, the two parents become almost equal in their ability to shape the embryo. He no longer talks of active forms and passive material, but rather of competing forces in the womb.
In his standard account of embryogenesis, an animal’s form is transmitted to the embryo by movements in the semen. They’re his units of inheritance, his information-carrying vehicles. He’s rather fuzzy about how the menses transmit information, but he must think that they do so as well – after all, they give the embryo at least a vegetable sort of life. But now, seeking to explain the phenomena of inheritance, Aristotle expands his vision. He argues that the semen and menses also seethe with movements that encode the individual features of both parents. The result is a dual-inheritance system: a set of paternal movements that encode the form – that make an embryo grow into a sparrow rather than a crane (or a human rather than a horse); and a set of movements provided by both parents that encode their informal features – that make it grow into an adult that resembles one parent rather than another. The relative power of these informal movements determines whom, if anyone, their child resembles. The idea of embryonic conflict probably came from Democritus or ‘Hippocrates’, but Aristotle’s model is subtler than either of those for he argues that the conflict is asymmetric. The menses’ movements exist only potentially. They’re there, but deactivated, and do their stuff only when the semen’s fall down on the job. Even now he can’t quite give mothers an equal hand.
To show what his model can do, Aristotle begins with the obvious fact that children come in two sexes. Sex determination was just the sort of problem to attract the speculative talents of the physiologoi, and Aristotle tackles their theories with glee. Anaxagoras argued that semen from the right testicle produces boys, semen from the left, girls. That gave fathers all the credit. One Leophanes, taking this argument to its logical conclusion, proposed gender selection by tying off a testicle before sex. Aristotle thinks this is nonsense, albeit because he doesn’t believe that testicles produce semen at all. Empedocles’ theory was characteristically complex. As Aristotle tells it, Empedocles had microscopic male and female parts, derived from each parent, fissioning and fusing in the womb. But it’s hard to work out what’s going here either because Aristotle dislikes this theory so (‘Empedocles was rather slipshod in his assumption,’ ‘the whole cast of this cause seems to be the product of the imagination’, ‘besides it is fantastic to imagine . . .’) and rather mangles it in the telling, or because it never made sense in the first place (Empedocles would write in verse). Aristotle does, however, pick out one weakness. It seems that Empedocles held that foetal sex somehow depends on the womb’s temperature, and Aristotle has a piece of evidence that decisively falsifies this claim. If you dissect live-bearing animals, he says, you often find male and female twins in the same uterus, so uterine temperature cannot determine sex. But in truth he doesn’t just say that; he positively crows.
In Aristotle’s own theory movements in the semen encode maleness, movements in the menses, femaleness. Since female movements appear only when the male’s are weak, every little girl represents a failure in her father’s semen. Aristotle tries to integrate his model with his embryo-genetic theory. Semen is hot, the menses are cold, and if the embryo is to be concocted properly, the two seeds must be present in just the right amount. The relative power of their movements are, then, somehow influenced by their relative heat. There’s a sleight of hand as he shifts between heat and movements, but the gist of the model is clear. When the semen ‘conquers’ the menses, the result is a boy; should it fail to do so for some reason then movements latent in the menses flourish and the result is a girl. So daughters are sired by feeble, or at least cold, fathers. This suggests a route to environmental sex determination and Aristotle claims that diet, paternal age, ambient temperature and the direction of the wind can all influence the heat of the semen and hence the sex of the child. Following Aristotle’s precepts if you want to father a daughter first take a long, cold shower, try your best and reflect that it beats ligating a testicle.
The conflict in the embryo is, however, just the beginning, for Aristotle distinguishes between the initial specification of sex and its consequences. He argues that the embryonic conflict directly determines just one small part of the embryo that influences the rest of the body to give all the other sexual characteristics. This is automaton-causality at work again. The distinction is very much like the modern one between ‘primary’ and ‘secondary’ sex determination. In 1944 Alfred Jost castrated foetal rabbits, found that they always turned out female, and so demonstrated that the critical organ of secondary sex determination is the gonad (it produces the hormones that determine the other secondary sexual characteristics: external genitalia, breasts, beards, etc.). Aristotle points out that castrated animals and eunuchs are feminized and infers from this that ‘some of the parts are principles [of sex determination], and when a principle is moved or affected many of the parts that are associated with it must change with it’. The conclusion should have been almost as obvious to Aristotle as it was to Jost: that the testes are critical to sex determination. But Aristotle is sceptical about testes and in love with the heart, so he argues that it is the embryo’s heart from which all other differences flow.
LXXIV
HAVING ESTABLISHED THAT a child’s sex is the outcome of a conflict between informal movements in the semen and menses, he argues that other informal, inherited variation is encoded in the same way. So he talks about noses – in particular, Socrates’ nose that, famously, was everything the ideal Greek nose was not. The ideal can be seen on the Artemision Poseidon or any statue of the time: high-bridged, straight and rather large. Socrates’ was small and snub. (In his Symposium, Xenophon has Socrates defend his snub nose, bulging eyes, wide mouth and flabby lips – they’re beautiful because they work better than yours, Socrates says.) Thus the foam visible in Socrates’ semen represents countless, minute movements that encode, very precisely, his characteristics, among them his snub nose.
Socrates was married to Xanthippe, and her menses have movements that encode her informal particulars too. But, as with her gender, they’re only potentially there – that is, they’re not necessarily expressed. Xanthippe was a notorious shrew and so we’ll give her a hooked nose. If Socrates’ semen totally ‘conquers’ Xanthippe’s menses, then their son, Menexenos, will be a clone of his father, snub nose and all. But if Socrates’ semen fails to conquer, then Xanthippe’s latent movements will be expressed and he’ll have a hooked-nosed daughter.
One of the oddities of Aristotle’s theory of inheritance, then, is that he thinks that most features – he is certainly thinking of facial features here – are sex-associated. Boys generally take after their fathers, girls after their mothers. I don’t know why he thinks this. After all, modern parents happily parcel out their children’s features between themselves (with a nod to grandparents) regardless of sex.* Actually, Aristotle recognizes that the association can break down. Should Socrates’ seminal movements mostly triumph, but his nose-movement fail, then Menexenos will have his mother’s hooked nose. In that case, Aristotle says, the nose ‘passes to the opposite’ bloodline.
GREEK NOSES. LEFT: HEROES’. RIGHT: SOCRATES’
The differences between the Aristotelian and Hippocratic theories of inheritance run very deep. Aristotle assumes that inherited traits have a discrete distribution: Menexenos may have Socrates’ or Xanthippe’s nose, but he can’t have a nose that’s something in between. ‘Hippocrates’ assumes a continuous distribution: depending on the precise proportions of parental seed, Menexenos may have either of his parents’ noses or anything in between. This implies that Aristotle’s hereditary movements are stable: they can be passed down more or less unaltered for many
generations; Hippocratic mixtures of hereditary fluids are not: each generation produces a novel mix.
This distinction is familiar and fundamental since it divides early modern theories of inheritance too. Aristotle assumes ‘particulate’ inheritance, ‘Hippocrates’ assumes ‘blending’ inheritance.* By particulate I do not mean that Aristotle supposes that actual particles are transmitted – that would be too Democritean – but only that the movements are stable and discrete. This has important consequences.
Aristotle sees that a good theory of inheritance must do more than explain why children look like their parents; it must also explain why children sometimes take after their grandparents or even more remote ancestors. Aristotle is rightly convinced that such reversions are common, but the example that he gives seems improbable. There was, he says, a woman who lived in Elis, a district of the Peloponnese, who had an adulterous affair with an Ethiopian. She bore by him a daughter who was white; this daughter, when she grew up, had a son who was black – even though the child’s father was presumably a Greek.* In Book I of The Generation of Animals, Aristotle says that his opponent’s theory can’t explain this and he’s right. And, although he doesn’t return to the case when setting out his own theory, it’s exactly the sort of phenomenon that it can explain. At least it can do so if he adds another layer of complexity to it.
Aristotle argues that sometimes the semen’s heat and movements are not quite powerful enough to reproduce the father’s features, yet not so weak as to default to the mother’s. In that case Menexenos will have his grandfather’s nose and will, in turn, transmit his grandfather’s nose to his sons. Menexenos may even have some more remote paternal ancestor’s nose, but this is less likely. Since such failures bring about a permanent, heritable change in the paternal movement we can call them, without anachronism, mutations. Aristotle seems to think that many, perhaps most, mutations cause ancestral reversions. His word for a permanent inherited change in movement is lysis, or ‘relapse’.
But knocking out Socrates’ nose movement doesn’t, by itself, explain how Menexenos can have his grandfather’s nose, for Aristotle must also explain where the information that specifies his grandfather’s nose is located. He therefore argues that the movements of Socrates’ semen encode not just his snub nose but also his father’s nose, his grandfather’s nose, his great-grandfather’s nose and so on for . . . how long? Aristotle doesn’t say. The movements of Xanthippe’s menses likewise encode the noses of her female ancestors. But none of these ancestral movements are expressed; they are mere potentials awaiting reactivation in the event of a failure of the active, parental movement. Generations of noses encoded in our bodily fluids – it’s a dizzying thought.
Were Menexenos to wind up with his grandfather’s nose, or even his mother’s hook, that wouldn’t be too bad, for Aristotle imagines that some mutations have much more drastic effects. People talk, he says, of a monstrous child who has the head of a ram or an ox, or a calf with a child’s head and suppose that they are human–animal hybrids. But they are not hybrids: it’s just that the movements in their parents’ semen and menses have failed to do their work. His examples – a child with an ox’s head (or the reverse) – suggest that he’s not only deflating popular belief, but also taking another swipe at Empedoclean preformationism. He wants to make sure that no smart-aleck student sticks up his hand and says: ‘I have a friend, who knows a woman, who had a cousin, who gave birth to a child with a calf’s head. Doesn’t that prove that Empedocles was right?’
It doesn’t. Aristotle can explain all sorts of monstrosities by appealing to the movements in the semen and menses. If Socrates’ nose movement is very weak then Menexenos could just have a general human nose.* And in the event of total failure he’ll have a monstrous nose – and by ‘monstrous’ Aristotle here means animal-like. Strip away all the human nose-specific movements embedded in the semen and all that’s left are the movements that make an animal. This view of mutational effects arises naturally from his von Baerian views of embryonic development. If embryos first develop features common to all living things (the nutritive soul) or all animals (the sensitive soul), and only later develop the characteristics of particular species, then it is easy to see how a failure of the semen to concoct the menses could cause development to halt part-way and so deprive a human foetus of its human features. It would be, in his vocabulary, very ‘imperfect’.
Any theory of inheritance that seeks to explain reversion (or atavisms, throwbacks, ancestral resemblance, skipped generations – they’re different labels for similar phenomena)* must assume that the units of inheritance are stable – that is, are particles in the broadest sense of the word – and that these particles can be silenced for generations and then be reactivated. These two ideas themselves recur. Aristotle explained reversion by allowing his movements to be actual or potential; Pierre-Louis Moreau de Maupertuis, the eighteenth-century philosophe who reported the first pedigree of an inherited trait, allowed his hereditary éléments to have more or less ‘tenacious arrangements’; Darwin, who devoted a chapter of his Domestication to atavisms, made his version of pangenesis run on gemmules that could be dormant; Mendel made his elementen dominant or recessive. Doubtless there are others.
In contrast to modern – post-seventeenth-century – taxonomy, functionalism and embryology, all of which are directly built upon Aristotelian foundations, there is no reason to think that Aristotle’s insight into the logic of inheritance has echoed down the ages. It is much more likely that nature has simply pointed, as she so often does, those who have interrogated her in the same direction. (As Aristotle, in another context, said of Democritus: ‘he was merely brought to it [the theory of substantial definition], in spite of himself, by the constraint of the facts’.) Of course, every theory gives a different account of how the units of inheritance combine and transmit, and only one of them was right. Aristotle’s was wrong too; but survey the admittedly dispiriting history of early genetics and one can conclude that until 1865, when Mendel presented his Versuche über Pflanzenhybriden to a sublimely indifferent world, there was no better theory than his.
RECIPE FOR
AN OYSTER
LIMNOSTREON – OYSTER – OSTREA SP.
LXXV
THE HARD MEN of Kalloni are its divers. Scorning SCUBA, they go down on the end of hoses attached to diesel-fuelled compressors to harvest oysters, scallops and mussels by the ton. Most of the divers are young, but I met one who could have been sixty. He was as slim as a cormorant and seemed to be built of olive wood. I asked him how many underwater hours he had. Five hundred last year. As a lifetime total, that impressed me since I’ve only done 150. Yes, he continued, last year I did 500, and 500 the year before and each year before that since I was a young man. We mostly dive in winter.
There are no numbers on the size or state of the shellfishery, but the bathymetry hints at former riches. South-west out of Skala, on a bearing for the Lagoon’s mouth, the flat bottom starts to be interrupted by circular hillocks that rise and fall on the sonar screen. These are the oyster reefs that the fishermen call kapalies. They say that there are a few thousand of them, or at least that’s how many there were. Since the 1950s dredging has flattened many of them. That’s now illegal, though fishermen will mutter that some people – always other people – still dredge while the Port Police look the other way, although whether out of indolence or venality is unclear. What is certain is that the oysters and scallops are in decline and that vast beds of mussels are spreading in their wake.
The Lagoon’s shellfish are Aristotle’s ostrakoderma – hard-shells. He describes their anatomies and something of their habits, mentioning, among others, the limnostreon (oyster), the kteis (scallop), the pinna (fan mussel), the lepas (limpet) and the beautiful kēryx, my trumpet shell.* He dwells on the porphyra, a snail that was once fished for a purple substance that it secretes in its hypobranchial gland. He says that there are many different kinds of porphyrai, that those in the features of
the Lagoon are small, and that snails from different places produce different-quality dyes. He’s probably distinguishing the banded murex, Hexaplex trunculus, the source of an indigo dye, and the spiny murex, Haustellum brandaris, the source of the true Tyrrhean purple, and local varieties of each. The most common species in Kalloni is H. trunculus which infests the bottom of the Lagoon and crowds into any baited trap for, as Aristotle says, although it feeds on bivalves it is also a scavenger. These snails are now a nuisance, but once they were the basis of a major industry. Mounds of broken shells, the earliest Minoan, the most recent Byzantine, can be found scattered across the Aegean. In Aristotle’s day the dye was worth its weight in silver.
Describing the anatomy of the oyster, Aristotle refers to its ‘so-called’ eggs. He plainly means its eggs, more precisely its gonads, which appear in the summer months as a milky sack. However, he denies the oyster, or any other shellfish, its gonads. He even denies them to the sea urchin and suggests that the ricci di mare is just where it stores its fat, even though the individual ova can just be seen with the naked eye. But if eggs aren’t eggs, how do oysters reproduce? Aristotle, rather surprisingly, says that they don’t. Instead, he argues that they generate spontaneously from the stuff in which they grow.
PORPHYRA – PURPLE MUREX – HEXAPLEX TRUNCULUS
LXXVI
WHEN ARISTOTLE SAYS that some animals generate spontaneously he means it:
Some animals are generated from animals whose shape is appropriate to their kinship. Others are generated spontaneously and not from kin. Some of these are generated from rotting earth and vegetation, as occurs with many insects, while others are generated inside animals themselves out of the residues from various parts.
The Lagoon Page 22
