Kimberly Pollard and Daniel Blumstein recently published a study (HT Ed Yong) examining whether group size correlates with the individuality of squirrel alarm calls:
Discriminating among individuals is a critical social behavior in humans and many other animals and is often required for offspring and mate recognition, territorial or coalitional behaviors, signaler reliability assessment, and social hierarchies. Being individually discriminated is more difficult in larger groups, and large group size may select for increased individuality–signature information–in social signals, to facilitate discrimination. Small-scale studies suggest that more social species have greater individuality in their social signals, such as contact calls....Extrapolating not unjustly from this, it seems that humans, the most social of all animals, should have the strongest drive towards uniqueness. So the desire for your own opinion, as opposed to just the best one, is probably an evolved tendency. We should all be similarly troubled by this.
[W]e show a strong positive evolutionary link between social group size in sciurid rodents and individuality in their social alarm calls. Social group size explained over 88% of the variation in vocal individuality in phylogenetic independent contrasts. Species living in larger groups, but not in more complex groups, had more signature information in their calls.