Final answer:
Multicellularity is a key innovation that allowed eukaryotes to diversify by enabling the division of labor among specialized cells.
Step-by-step explanation:
Multicellularity evolved early in eukaryotes and is a key innovation that allowed eukaryotes to diversify. Multicellularity is the characteristic of many eukaryotes where cells remain small while exhibiting specialized functions. This division of labor among specialized cells allows for efficient resource utilization and adaptation to different environments.