Original source for Martin Nowak's “snuggle for survival”?

A quick Internet search shows many essays, blogposts, etc. about Martin Nowak's idea that the “snuggle for survival” is an important part of evolution.

Is there an original publication by Martin Nowak that first coined the phrase "snuggle for survival"? I.e. what's the original source for this term? Was it in a paper or essay that he wrote? I'd love to read it. Thanks!