🤔 I keep hearing pop scientists say that if we ever discover life elsewhere in the universe, it'll almost certainly be single celled microbial.

I disagree. It will almost certainly **_include_** prokaryote analogues, but will also include multicellular organisms. Why? Because the whole point of cells joining forces and becoming an animal is that the cells can specialize. Microbes are mostly locked in an eternal war with each other. For every new weapon or trick that evolves, a new defense also evolves. That's why we have white blood cells - to be specialized fighters. Every cell has a finite energy budget - if it prioritizes one thing (making a certain protein) it must sacrifice something else. Only specialization and cooperation scales up in the microbial war.