Words at Play : Words With Remarkable Origins, Vol. 2
A gregarious person is social; she enjoys being part of the crowd.
If that sort of sociability seems distinctly human, the word makes direct connections to the animal world: greg- means "flock or herd" in Latin (where gregarius means "of or relating to a flock").
Fittingly, gregarious belongs to its own linguistic group: aggregate, congregate, segregate and even egregious, which means "conspicuous" (e- means "out of") because it stands out from the crowd.