Family Trees

Diagram of the 11 groups Susan studies. The red lines indicate that one group split off from another, and the years give the date of each split. Diagram: S. Perry.

Monkeys live in groups of around 10-30 members.  Each group is made up of related females and their offspring and unrelated males, who join the group as adolescents after leaving the group of their birth.  If a group gets too big it will fission, or split apart, along matrilines: one of the older females will leave the group with all of her daughters.  When Susan first came to Lomas, she studied just one group: Abby’s, named after the alpha female at the time.  Later, she began to study two other groups: Rambo’s group and Pelon group.  Thirty years later, Susan monitors eleven different groups, all products of fissions and all descended from one of these three groups.  Celeste’s group fissioned off of Abby’s in 2012, while Flakes is an earlier fission product of Abby’s group, from 2003.