While plants survive by photosynthesis, animals and fungi both survive by respiration. Animals and fungi both breathe oxygen and eat sugar; both digest their food, breaking cells down using enzymes and absorbing their inner nutrients; and both share a much more recent common ancestor than either do with plants, which diverged much earlier. At the dawn of multicellularity, fungi and animal life would have been extremely similar. And yet one lineage (animals) went on to evolve neurons and brains, and the other (fungi) did not. Why?
