The Grandmother Hypothesis In the 1980s, American anthropologist Kristen Hawkes observed Hadza hunter-gatherers in Tanzania, and realized that the older women spent their time collecting food for their grandchildren. This freed up the mothers to have more children. Hawkes hypothesized that the fittest grandmothers had the most grandchildren, which created selective pressure for longevity well past menopause in humans (as opposed to other apes, whose lifespan ends just after their childbearing years). Hawkes suggested that