This episode turned out to be both long and hard. Feel free to snicker at this point. It was long because I couldn’t resist the numerical pun. To match this episode’s number with its subject, I had to squish together the development of eukaryotes with the development of sexual reproduction. Fortunately, they may both have come about because of interactions taking place within microbial mats. It was hard because the subject turns out to be more complicated than I had thought.
There are disadvantages to sexual reproduction as compared to asexual reproduction. You have to find a compatible mate, and then, only half of your genetic material is transmitted to the next generation. Even worse, many creatures have males and females. This means that as much as half of your population is unable to produce offspring. Those lazy men. Regardless of the disadvantages, most eukaryote species, over 99%, use sexual reproduction, including us.
Here’s an article on some fossilized fish that provide some of the earliest evidence of body to body mating.
Here’s an article on fossils from much earlier of creatures that mated by spawning.