Butimportantquestionsremain, hesays. For example, malehumpbackwhalessometimessing as they moveinandout of competitivegroups, but researchers don'tknowwhatrole the songs playinmating.
The rate at which an epidemic spreads to lower-risk groups depends a great deal on whether different groups mate mainly among themselves (assortative mating) or whether they mate a lot with other people (disassortative mating).