The fitness of any evolutionary unit can be understood in terms of its two basic components: fecundity and viability. The trade-offs between these fitness components drive the evolution of many life-history traits in extant multicellular lineages. Here, I show that the emergence of individuality at a higher level during the uni-multicellular transition can also be a consequence of these trade-offs. I argue that germ-soma separation evolved as a means to counteract the increasing costs of larger multicellular colonies.
Volvocalean green algae are uniquely suited for studying this transition...