Alan Burdick writes in the New Yorker:
This week, a team of researchers at Harvard published the largest and most definitive study of the subject to date, and the findings are compelling. “Men who wore non-boxers”—that is, briefs and their confining kin—“have significantly lower concentrations of sperm and lower sperm counts,” Jorge Chavarro, a fertility researcher at the Harvard T. H. Chan School of Public Health and a member of the research team, told me. “It’s a numbers issue.”
I believe the study is accurate because I only wear boxers and I have four kids. I never liked my package to be tight. It just feels good letting it loose. The only downside is that you can get horny easily and it will show. In any rate, I have been telling my wife to get rid of all of the kids’ briefs and get them to boxers. This study provides a good reason to switch.