In areas covered by snow most of the year, body decoration is often sacrificed for a more concealing white pelage or plumage. Hole-dwelling birds can have more brightly colored plumage than birds which nest in exposed places in the fields. The same sorts of varying pressures occur, between races and subspecies. Furthermore, most social organs are multi functional, and a compromise must often be made. Likewise, the social situation varies throughout the range of the species.
Some areas can support dense populations, other areas only a few scattered souls.
David Klein, working with two deer populations illustrated how population density and severity of the winter affected selection for body and weaponry size from one population to the next. Undoubtedly, the interrelationships between the diverse physical and social climates experienced by man throughout the world have been responsible for the varying pattern of his social organs skin pigment, hair texture, armpit odor, eye color, nose size -most of the obvious things which, vary among human races. This brief review of the social organs of other animals can now serve as a sketchy trellis on which the story of our own social organs can grow.