He has a recent book which deals with the subject: "SuperCooperators: Altruism, Evolution, and Why We Need Each Other to Succeed". One review is here
Nowak achieved some not-so-desirable publicity recently with his role in the "Kin Selection debacle" in Nature.
Nowak discusses cultural evolution near the start of the first video, but - as with most writers on the subject of cooperation - Nowak seems to be more interested in game theory than symbiosis and cultural evolution.
Here's Martin_Nowak's Wikipedia page. It says - among other things - that he's a catholic, has received Templeton Foundation grants and ran the Evolution and Theology of Cooperation program at Harvard University.
Supercooperators: The mathematics of evolution, altruism and human behaviour
Martin Nowak on Game Theory in a Hyper-public Life
Martin Nowak - Emergence