As shown by the use of surnames (not to mention family reunions), humans attach a lot of importance to knowing who their relatives are. So, it seems, do wasps, wildflowers, and many other members of the plant and animal kingdoms. Pfennig, a biologist at the University of Illinois, and Sherman, a professor of animal behavior at Cornell University, explain how-and perhaps why-the process works.
Some organisms, such as primates and frogs, recognize their kin by their distinctive physical characteristics, sensing these directly by sight, sound, or smell. Other organisms pick up indirect clues from place or time as to who their relatives are. Bank swallows, which nest in colonies on sandbanks, use both methods to identify their young. For about three weeks after hatching, parent bank swallows will feed any nestlings they find in their burrow. After the chicks learn to fly, however, broods mix extensively, and the parents are forced to turn to direct means of identification, picking out their own young by the distinct vocal signatures that chicks develop by the time they are 20 days old.
Such recognition "labels" can reflect genetic traits, as in the case of certain sea squirts. These brainless marine animals, the authors write, "begin life as planktonic larvae that eventually settle on a rock and multiply asexually to form an interconnected colony of structurally and genetically identical animals." Sometimes, two genetically similar colonies merge. If a colony tries to join another unrelated one, however, the latter emits poisonous substances to repel the invader. . .