The author hypothesizes that, based on past findings about temperature and sperm production, a kilt, specifically one worn in the undergarment-free "regimental" style, would be an ideal environment for sperm production. Kompanje searched through related research, focusing on statistics in Scotland and noting along the way that 70 percent of kilt-wearers choose to go regimental. Kilts (at least in Scotland or other countries where they're more commonly worn) might also be psychologically valuable, increasing feelings of masculinity when worn. Kompanje goes so far as to write that a downturn in Scottish fertility is correlated with the frequency of kilts being worn, although he admits it's still somewhat speculative until a randomized trial happens. Gentlemen, put on your kilts for science.