No scientific evidence, eh? Tell me, what classification do mushrooms and jellyfish fall into? Are they multicellulars, or communities of single-cellulars?
They are multi-cellular. And the jump from single-celled to many cells is humongous particularly in animals, a jump which could never have occurred. As to the ribosome, that has nothing to do with multi-cellularity, it is the splitting of organs and functions that is the problem.
Most fungi are neither multi-cellular, nor unicellular. They are both, at various times. Some are actually mobile in their unicellular stages. They exist as unconnected, gene-exchanging unicellulars, until chemical signals draw them together to form the stalk. For most of them, most of their existence is unicellular.