When you marvel at the brilliant colors of a peacock's tail or enjoy the trill of a songbird, you might pause to consider that those creatures' ancestors probably didn't have a lot of friends.Many animals display visual or auditory cues that contain messages like, "I would be a desirable mate" or "I am very strong; don't come into my territory." Species that lack such "quality signals" – including humans, crows and dolphins – probably evolved in smaller social groups where everyone already knows what everyone else is like, according to Michael Sheehan, assistant professor of neurobiology and behavior.
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