In a recent experiment, scientists have observed how a single-celled algae evolved and developed multicellular structures in response to predators. This study aims to test the hypothesis that evolution of simple organisms to more complex ones may have been brought about by predation. Here is an excerpt of their discussion in the paper:
Our results show that the transition to a simple multicellular life cycle can happen rapidly in response to an ecologically relevant selective pressure. By increasing in size beyond the “predation threshold” of a filter-feeding predator, multicellular C. reinhardtii that evolved from an ancestrally unicellular lineage are protected from predation for at least part of their life cycle. Under selection for increased size, formation of multicellular structures may be an easier route than increasing cell size because of trade-offs imposed by scaling relationships (chiefly the reduction in surface-area-to-volume ratio), because more mutational paths are available, and/or because available mutations have fewer or less severe pleiotropic effects.
(Image credit: M.D. Herron et al)