“All happy families are alike; each unhappy family is unhappy in its own way.” For multicellular evolution, he told me, the logic is turned around: every single-celled organism that evolved toward multicellularity took a unique path. It became “happy”—or, rather, more evolutionarily fit—in its distinctive way. Single-celled organisms remained, well, similarly single-celled. It is, in Ratcliff’s words, “a reverse Anna Karenina situation.”
