One prerequisite for the evolution of multicellular organisms was the invention of mechanisms by which cells could adhere to one another. At some point in our history, dividing cells no longer went their separate protozoic ways in the primordial oceans, but instead found that by maintaining an association, by sticking together but not fusing, numerous evolutionary advantages became possible. The subsequent development of specialized tissues and organs depended on the elaboration of incredibly sophisticated, regulatable cell-to-cell adhesion mechanisms which are known to operate in...