suppresses the reproduction of subordinates. This loss of
reproduction is the major cost of sociality. A major benefit
is increased survivorship. In yellow-bellied marmots, net re-
productive rate increases as the number of matrilineal mem-
bers increases, but decreases in the largest matrilines. Re-
productively suppressed subordinates apparently choose
the best alternative available to them by remaining in the
social group until they can escape suppression, bud off to
form a new group, or take over the dominant position
within their group or an adjoining group.Evolution of Sociality in Marmots: It Begins with Hibernation 367