Queuing up their ejaculate and/or shedding unnecessary sperm cells. Men’s reproductive systems are constantly at work, just like those of women. Every day, a man is queuing up sperm readying for just the right moment to ejaculate. His behavior is carefully tailored to make his ejaculation as potent as possible. Masturbation, for instance, gets rid of older sperm that will be less viable. Ejaculation into a long-term partner will be different depending on how long she’s been around; she gets a bigger, juicier load after an aggressive bout of copulation if she had the opportunity for infidelity (pornography exploits this reaction; when a guy sees porn, he becomes instantly aroused by the act of another guy having sex; his urge is to ejaculate into the woman so he can compete for the chance to fertilize her). Ejaculating into a new partner might mean a big, fat, juicy load replete with the most potent sperm cells possible.