The reactions against Cartesianism in analytic philosophy of mind have made possible a revival of the Aristotelian term for a human being -- the idea of a rational animal. Descartes famously (or infamously) dismisses this description in Meditation II, where he denies that the cogito can be identified with the Scholastic animale rationale, on the grounds that it is requires categories that cannot be derived from the solipsistic stance of self-consciousness.
By contrast, in the work of Donald Davidson, Alastair MacIntyre, and especially John McDowell, the idea of a rational animal has resurfaced. In doing so, we must confront two questions: (a) what makes an animal rational? and (b) why must the rational entity, so conceived, be an animal?
To be rational, on a model broadly shared between Davidson and McDowell, is to capable of making moves within what Sellars called "the space of reasons": it is to be capable of asserting, of giving reasons for ones assertions, and to be capable of asking others for the reasons for their assertions. McDowell emphasizes that this point holds not only for episodes of knowing, as in Sellars, but for all thought as such. To put the point in terms developed by Bob Brandom, to think is to make a material inference.
An animal is rational if it is not merely sentient but also sapient. "Sentience" entails consciousness, affectivity, and responsiveness to changes in its environment. An animal may be sentient and yet be extremely clever in manipulating objects in its environment, even its fellow creatures. "Sapience" differs in that sapience entails a capacity for reasoning and for recognizing that it is taking up a view on the world and not merely occupying a place in an environment. (Heidegger's distinction between Welt and Umwelt, mediated through Gadamer, is an important influence on McDowell's version of this distinction.)
But McDowell, more than his fellow Sellarsians Brandom and Rorty, insists that the bearer of rationality must be an animal. It must be something intrinsic to the way of life of a particular kind of animal, a human being -- an animal that can acquire culture, Bildung, Geist. Thinking and knowing are part of how we are as animals, as web-weaving is part of how a spider is as an animal. And it is part of McDowell's critique of "para-mechanism" in philosophy of mind -- Millikan and Dennett in particular, also fellow Sellarsians -- that they lose their grip on the fact that what is rational must be animal, and what is animal must be rational.