Scu (here) and Peter Gratton (here) have opened a discussion about Levinas' concept of the other, specifically regarding the problem of alterity and the human/animal distinction. Peter does a good job summarizing a basic problem with Levinas' account:
He wants to say both that the Other as such is wholly other, unique, and non-subsumable under a form of knowledge, and he wants to say the other is human. But there is no a priori rule one can put into place, given his radical claims for alterity, that would have one always already identify otherness as human, as non-animal, and so on.
In fact, I think it's surprising that more people working on the concept of the other don't acknowledge how conservative Levinas' account is (even after Beauvoir points out how he utilizes the 'Feminine is the other' trope...). Nor is enough attention paid to a very concrete ethical failure (included in The Levinas Reader, on page 294), Levinas' response to Israel's invasion of southern Lebanon. From an interview on September 28, 1982:
[Shlomo Malka]: Emmanuel Levinas, you are the philosopher of the 'other.' Isn't history, isn't politics the very site of the encounter with the 'other,' and for the Israeli, isn't the 'other' above all the Palestinian?
[Levinas]: My definition of the other is completely different. The other is the neighbour, who is not necessarily kin, but who can be. And in that sense, if you're for the other, you're for the neighbour. But if your neighbour attacks another neighbour or treats him unjustly, what can you do? Then alterity takes on another character, in alterity we can find an enemy, or at least then we are faced with the problem of knowing who is right and who is wrong, who is just and who is unjust. There are people who are wrong.
That's a rather circuitous route to say, 'no, that's not the alterity I am talking about,' but I suppose that Levinas didn't want to admit that his concept of the other is not so radical after all. And to think that the volume's editor commends the interview for "its rigour and clarity."