Enlightenment rationality means declining violence?

I'll have to put Steven Pinker's new book, The Better Angels of Our Nature: Why Violence Has Declined , as it seems to be one of the major talking points of the year (especially in the UK, for some reason). Here is a review by John Gray in Prospect Magazine disagreeing with Pinker's argument that we have made progress in containing violence.

Science and humanism are at odds more often than they are at one. For a devoted Darwinist like Pinker to maintain that the world is being pacified by the spread of a particular world view is deeply ironic. There is nothing in Darwinism to suggest that ideas and beliefs can transform human life. To be sure, there have been attempts to formulate an idea of progress in terms of competing memes—vaguely defined concepts or units of meaning that are held to be in some ways akin to genes—although nothing like a scientific theory has been developed. Even if there were such things as memes and they did somehow compete with one another, there is nothing to say that benign memes would be the winners. Quite to the contrary, if history is any guide.