I’d change human biology by reducing sex drive to one-two month a year.
It would change our species in several ways.
First, women wouldn’t have periods. If you can’t get pregnant every month, there’s no need for preparing for pregnancy and going through the whole hassle.
Second, it would significantly reduce natality. You’d have one chance a year to get pregnant. Less kids is not unwanted in such a crowded place as the planet is today.
People, especially women, would go into puberty later than they do nowadays, which would “awake” the sex drive later in life, when you’re actually old and mature enough to deal with sex and kids.
Way less rape, cheating, unwanted pregnancies, sexual perversions, abortions and obsessing over sex in general.
People would have time to focus on more productive things in life, and see sex and relationships on emotional, rather than physical level.