Maja Adamska, Sandie M. Degnan, Kathryn M. Green, Marcin Adamski, Alina Craigie, Claire Larroux, Bernard M. Degnan [creativecommons license] via Wikimedia Commons
The oldest surviving multicellular animals (or metazoans)—sponges—are simple organisms. Though they lack organs and muscles, they possess valuable genetic information that explains how cells first came to cooperate and behave as a collective. Understanding the mechanisms underlying the development of multicellularity can help us to define what it really means to be an animal.
Lab Anim. (NY) 39, 255 (2010).
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