In his History of Animals, Aristotle makes the following comment (HA VII 6, 585b28-586a4):
“And from deformed [parents] deformed [offspring] comes to be, just as lame come to be from lame and blind from blind, and in general they resemble often the features that are against nature, and have inborn signs (καὶ ὅλως τὰ παρὰ φύσιν ἐοικότες πολλάκις, καὶ σημεῖα ἔχοντες συγγενῆ), such as growths and scars. Some of such features have even been transmitted through three [generations]: for instance, someone who had a mark on his arm and his son was born without it, but his grandson had black in the same place, but in a blurred way. Such things happen rarely, and for the most part offspring with the body-parts intact come to be from mutilated parents, and nothing has been settled definitely about them (καὶ οὐδὲν ἀποτέτακται τούτων). And they [i.e., the offspring] resemble the parents or their ancestors further away, and sometimes nothing like that. And they [i.e., the parents] can also transmit [features] through several generations: for instance, in Sicily a woman committed adultery with a man from Ethiopia – for the daughter did not become an Ethiopian, but her daughter did.”
According to this passage, there is a possibility that parents may pass on their bodily imperfections to their offspring, although – apparently – this does not happen necessarily in each case or even in most cases. Nevertheless, when it comes to the ideal state in the Politics, Aristotle believes that it is up to the lawgivers to put regulations in place concerning marriages and child-production (e.g., about who should marry whom and at what age, and about at what age parents should produce offspring and during what seasons or what winds and in what bodily conditions) to make sure that from the start ‘the bodies of the children being reared come to be as good as possible’ (Pol VII 16, 1334b29-30: ὅπως βέλτιστα τὰ σώματα γένηται τῶν τρεφομένων). Producing offspring is a matter of public service (Pol VII 16, 1335b28-29: λειτουργεῖν … πρὸς τεκνοποιίαν; cf. Pol VII 16, 1335b36-37), and producing good offspring is among the markers of the quality of the ideal city (Pol IV 12, 1296b17-18): it is thus very important that lawgivers prevent failures in the reproductive processes leading to defective offspring as well as promote conditions that are most conducive to the production of male offspring that is perfect in both body and mind (cf. Pol VII 16, 1335b30-31).
Although Aristotle does not in this context specify the exact mechanisms that explain this supposed causal relationship between the qualities of the bodies and minds of the parents and the level of the perfection of their offspring, the general picture is clear (Pol VII 16, passim): (1) men should not reproduce until their semen is fertile and their internal heat fully developed, and should stop soon after their mind has reached its prime (i.e., they should reproduce between the ages of thirty-seven and fifty-five); (2) women should not reproduce until their internal heat has fully developed and until their level of moistness is just right (i.e., they should reproduce between the ages of eighteen and thirty-six); (3) both men and women should have bodies that hold a middle between that of an athlete and that of someone requiring medical treatment and not well capable of exertion, which means that they should follow certain diets and exercise their bodies in a non-violent manner and for the sake of activities appropriate for free people.
In the next couple of weeks, I hope to find out how this account of how to produce good offspring in the Politics relates to Aristotle’s more technical views in the biological works about the heredity of bodily features, including perhaps the quality of the offspring’s blood and hence his natural character traits. Traditionally, studies of Aristotle’s theory of inheritance have focused on the teleological mechanisms for the transmission of form (how is it that a ‘human begets a human’?), the determination of the sex of the offspring, and the inheritance of familial resemblances due to form (e.g., Socrates passing on his snub nose to his children), which all in one (complex) way or another are related to the active motions transmitted through the male semen and the passive motions present in the female menses. However, Aristotle’s discussion in the Politics suggests that the bodily features the offspring ends up having might not be entirely accidental either. For instance, is Galen right when he claims that for Aristotle, too, humans have the character traits they have in virtue of the mixture of the blood they receive from their mother?
 QAM 7, 791.6-9: ‘that Aristotle, too, believes that the soul’s faculties depend on the mixture of the mother’s blood (τῇ κράσει τοῦ τῆς μητρὸς αἵματος), from which he says our own blood comes to be, is clear from what he says.’ Cf. also QAM 7, 795.11-14.