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. Author manuscript; available in PMC: 2014 Sep 7.
Published in final edited form as: J Theor Biol. 2013 May 3;332:171–180. doi: 10.1016/j.jtbi.2013.04.031

Fig. 1.

Fig. 1

Stages of the division of labor. 0 (No. division of labor): coresiding adults choose their time allocation (foraging and child-caring) as if they play a non-cooperative Nash game. 1 (Pure division of labor): an age-specific division of labor occurs, with the age-1 devoting more time to foraging and the age-2 devoting more time to child-care. 2 (Menopause): a further division of labor occurs, when the age-2 becomes sterile and thereby avoids the energy expenditure of giving birth. This enables her to switch more time from foraging (generating energy) to child-care. 3 (Filial piety): a further division of labor occurs, when the age-2 reduces or stops foraging to acquire energy for her own subsistence. This enables her to switch even more time from foraging to child-care.