What do scientists talk about when they get together? All sorts of random things. Welcome to the first installment of Science With Friends, a new series where friends write about science. I hope it is both entertaining and informative. Enjoy!

Why do men and women exist? Why are there not just…people? Peace, dear reader—I’m not channelling Yoko Ono’s Twitter feed here, but addressing the biological question of why so many creatures (but not all!) are divided into male and female.

The simplest way to reproduce is to just make an identical copy of yourself. This is mainly how bacteria, the oldest and most numerous organisms on the planet, get it done. But plenty of more complex beings, such as plants and animals, can reproduce the same way, through cuttings, budding or other similar means. This asexual sort of reproduction has many advantages—there’s no need to wander around searching for a mate and all one’s tried-and-true genes get passed on, instead of taking a chance and ending up mixed and matched with some rando’s janky DNA.

Asexual reproduction does not result in absolutely unvarying organisms—there’s inherent randomness in the biochemical processes governing life and errant radiation or chemicals can also come by and scramble things. These generate genetic variation, on which the evolutionary processes of selection and drift can act. But this way is slow and conditions, whether they are climatic or pathogenic, can change fast. When a new critter comes along that wants to hitch a ride on you/feed on you/liquefy you from the inside out, it would helpful to have the tools to deal with it sooner rather than later. This is where grabbing some DNA from another individual of your species can come in handy—they just might have what you need to fend this threat off. This is sexual reproduction. Continue reading →