In After Virtue, Alisdair MacIntyre often refers to Aristotle's "metaphysical biology" with disapproval. What exactly does he mean by this? I assume it is more specific than Aristotle's metaphysics or his biology?
In After Virtue I had tried to present the case for a broadly Aristotelian account of the virtues without making use of or appeal to what I called Aristotle's metaphysical biology.
MacIntyre rejects Aristotle's 'metaphysical biology', p.196:
First, although this account of the virtues is teleological, it does not require any allegiance to Aristotle's metaphysical biology
and also p.163 (full quote further below):
If we reject that biology, as we must...
The clearest clue of what he means is found on p.58, although this is still not that clear to me. He basically equates it with the assertion that the telos of man is the good life:
Aristotelian tradition-whether in its Greek or its medieval versions - involve at least one central functional concept, the concept of man understood as having an essential nature and an essential purpose or function; and it is when and only when the classical tradition in its integrity has been substantially rejected that moral arguments change their character so that they fall within the scope of some version of the 'No "ought" conclusion from "is" premises' principle. That is to say, 'man' stands to 'good man' as 'watch' stands to 'good watch' or 'farmer' to 'good farmer' within the classical tradition. Aristotle takes it as a starting point for ethical enquiry that the relationship of 'man' to 'living well' is analogous to that of 'harpist' to 'playing the harp well' Nicomachean Ethics, 1095a 16). But the use of 'man' as a functional concept is far older than Aristotle and it does not initially derive from Aristotle's metaphysical biology. It is rooted in the forms of social life to which the theorists of the classical tradition give expression. For according to that tradition to be a man is to fill a set of roles each of which has its own point and purpose: member of a family, citizen, soldier, philosopher, servant of God. It is only when man is thought of as an individual prior to and apart from all roles that 'man' ceases to be a functional concept.
Every activity, every enquiry, every practice aims at some good; for by 'the good' or 'a good' we mean that at which human beings characteristically aim. It is important that Aristotle's initial arguments in the Ethics presuppose that what G .E. Moore was to call the 'naturalistic fallacy' is not a fallacy at all and that statements about what is good - and what is just or courageous or excellent in other ways-just are a kind of factual statement. Human beings, like the members of all other species, have a specific nature; and that nature is such that they have certain aims and goals, such that they move by nature towards a specific telos. The good is defined in terms of their specific characteristics. Hence Aristotle's ethics, expounded as he expounds it, presupposes his metaphysical biology. Aristotle thus sets himself the task of giving an account of the good which is at once local and particular -located in and partially defined by the characteristics of the polis-and yet also cosmic and universal. The tension between these poles is felt throughout the argument of the Ethics.
We have in the course of this account identified a number of points at which Aristotle's account of the virtues can be seriously put in question. Some of these concern parts of Aristotle's theory which not only have to be rejected, but whose rejection need not carry any large implications for our attitudes to his overall theory. So it is, I have suggested, with Aristotle's indefensible defence of slavery. But in at least three areas questions arise which , unless they can be answered satisfactorily, endanger the whole Aristotelian structure. The first of these concerns the way in which Aristotle's teleology presupposes his metaphysical biology. If we reject that biology, as we must, is there any way in which that teleology can be preserved?...any adequate teleological account must provide us with some clear and defensible account of the telos; and any adequate generally Aristotelian account must supply a teleological account which can replace Aristotle's metaphysical biology