The changes in sperm count are interesting, although I'd be as likely to explain that as some sort of testosterone effect from the virtual presence of other males. Porn causing an effect doesn't surprise me too much -- the entire reason we created it was because it did -- we respond physically to psychological stimulation. However, I'd be very surprised by the competitive gang-sex theory -- extremely so. Even bonobos, who are most sexually similar to us, and have huge amounts of recreational and social sex in all combinations, don't follow that pattern at all, as far as I know, and I've never heard any other arguments for it, in 15 years of ongoing academic curiosity about human sexuality and sexual evolution. I'll have to look up his book and check it out -- I'm not sure, but I think that some of Elisabeth Lloyd's arguments from The Case of the Female Orgasm may also apply as critiques here, even though the topics are slightly different. The book is a bit dry and academic, but it's fascinating, and well-worth reading.