SELF RECOGNITION MOLECULES. “The original self-recognition molecules in protoeukaryotic gametes might have engaged in homotypic interactions, like present-day cadherins that adhere to one another. Alternatively, the interactions might have been heterotypic, like present-day integrins that adhere to intercellular adhesion molecules (ICAMs).”
http://cshperspectives.cshlp.org/content/6/3/a016154.full