Ancient Greek Genetic Theory

Aristotle's writings were transmitted to the Middle Ages, so right or wrong he had a lasting impact. While one wouldn't want to say Aristotle understood genetics thoroughly, he helped dispel some of the incorrect earlier genetic theories. By (ancient) genetic theory is meant theories about coming into being and reproduction, rather than DNA, although, as something to note in passing, Tom Vinci and Jason Scott Robert (2005) would credit Aristotle with coming up with the idea:

"It is my contention that Aristotle's principle of the 'unmoved mover' perfectly describes DNA: 'it acts, creates form and development and is not changed in the process.'"

In the final play of Aeschylus' trilogy The Oresteia, Orestes is on trial for murdering his spouse-killing mother. The goddess Athena presides and pronounces the deciding vote. Since she had been born without a mother, Athena says that the mother is unnecessary in creation. With her verdict, she saves Orestes from further torture at the hands of matricide-avenging Furies. From this tragedy, we can see that the Greeks had genetic theories, even if they seem a bit odd to us.

Aristotle on Preformationism and Epigenetics

Among the philosopher-scientists of ancient Greece were competing theories of reproduction/conception. Aristotle, [On the Generation of Animals (GA)], is a central figure in our knowledge of ancient theories of reproduction; albeit about animals, but applicable to humans. Based on his observation and logic, he argues the alternatives don't work.

The earlier theories may be lumped together under the modern label preformationism, which views creatures as created entire, but in miniature. Aristotle's replacement theory is referred to as epigenetics, which says creatures evolve; change exists and it's more than accidental. Most of the following is based on my understanding of Tress' article, "Aristotle against the Hippocratics on Sexual Generation: A Reply to Coles."

Preformationists Discount the Role of the Mother

A typical preformationist, like Euripides, thought that the father was like a plough and the mother a field, with the father transmitting the genetic material into something like an incubator.

"Also in [Plato's] Timaeus (91), men are said to "sow in the womb, as in a field, animals unseen by reason of their smallness."
-Preus

[For more on Plato's genetic theory, see "Greek Theories on Eugenics," by David J. Galton; Journal of Medical Ethics Vol. 24, No. 4 (Aug., 1998), pp. 263-267]

Preformationists argue the seed so planted has all the data required to produce a complete person.

A problem in preformationists' genetic theory is that children can and often do take after their mothers. An explanation for this involves an old version of the nature vs nurture debate. Because the mother provides the milieu and nourishment in which the embryo grows she affects the appearance. The Pre-Socratic philosopher Empedocles, a preformationist, seems to have dealt with this problem by positing two sets of sperma, one from each parent. These two sets then fit themselves together in the womb -- like a magic puzzle.

Where Does the Seed Come From?

Sperm supposedly came from the brain and then filtered down through the body to the testicle reservoirs. A related theory, the pansomatic or pangenetic theory [based on Darwin, but used to refer to an ancient genetic theory that, Coles argues, Aristotle essentially agrees with even if he denies its validity], has a different idea of the origin of the seed. The pansomatic theory holds that "homoiomeries" or sperma (generative fluid) come from all parts of the parents' bodies and are composed of the four bodily forms: blood, phlegm, yellow bile, and black bile -- the four humors. Since the sperma come from all parts of the body, the seed can reproduce all parts of the body.

Resemblance is dependent on which sperma is dominant. Gender depends on factors like left or right testicle or the location or temperature in the womb.

Aristotle's Genetic Advances

In Book I of GA, Aristotle lists reasons for rejecting earlier genetic theory. For example, Aristotle argues that the pansomatic theory fails to provide an organizing principle and does not account for why a child might look more like a relative who did not participate in the conception than either of her parents.

Aristotle uses his four causes to explain his theory of generation.

"There are four causes underlying everything: first, the final cause, that for the sake of which a thing exists; secondly, the formal cause, the definition of its essence (and these two we may regard pretty much as one and the same); thirdly, the material; and fourthly, the moving principle or efficient cause."
GA Book I

Preus produces the following scheme for the four causes in connection with Aristotle's theory of genetics:

1. Survival of the species is the final cause;
2. the formal cause (eidos) is present as potential in the matter and in actuality in the semen;
3. the matter (material cause) is provided by the mother;
4. the moving cause is the contribution of semen, which Aristotle thinks comes from blood, from the father. This semen contains the guiding principle of pneuma.

Aristotle improved the genetic theory of ancient Greece, but he got quite a bit wrong. For starters, he didn't know about ovaries, and says testicles serve as weights:

"For the testes are no part of the ducts but are only attached to them, as women fasten stones to the loom when weaving; if they are removed the ducts are drawn up internally, so that castrated animals are unable to generate...."

For more on Aristotle's theory of reproduction and the problems in it, see:

• _{"Aristotle against the Hippocratics on Sexual Generation: A Reply to Coles," by Daryl McGowan Tress; Phronesis, Vol. 44, No. 3 (Aug., 1999), pp. 228-241}
• _{"Galen's Criticism of Aristotle's Conception Theory," by Anthony Preus; Journal of the History of Biology, Vol. 10, No. 1 (Spring, 1977), pp. 65-85}
• _{"Galen's Conception Theory," by Michael Boylan; Journal of the History of Biology, Vol. 19, No. 1 (Spring, 1986), pp. 47-77}
• _{"Biomedical Models of Reproduction in the Fifth Century BC and Aristotle's 'Generation of Animals'," by Andrew Coles; Phronesis, Vol. 40, No. 1 (1995), pp. 48-88}
• _{"Aristotle on the Mechanism of Inheritance," by Devin Henry; Journal of the History of Biology Vol. 39, No. 3 (Autumn, 2006), pp. 425-455}
• _{"Aristotle and Modern Genetics," by Tom Vinci and Jason Scott Robert; Journal of the History of Ideas Vol. 66, No. 2 (Apr., 2005), pp. 201-221}

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