Demography tidbits part II: The importance of grandmas

After Simeon was born we were delighted to have both my mom and Rachel's mom come over for a week or so to help out with the newborn. Around this time, my mortality and aging class was discussing the reasons that have been hypothesized for why, out of all the known primates and mammals, humans are the only ones that 1) have an "adolescent" period where they are cared by their parents after lactating but before they are self-sufficient, and 2) live beyond menopause.

This is one of the leading explanations: hunter-gatherer societies use knowledge and skills-intensive methods for finding food, , which allows us to enjoy calorie-dense meat, in contrast to our hominid relatives that just forage for leaves. Learning and developing these methods require a longer learning time, which explains the longer adolescence. However, taking care of teenagers (yes, contrary to popular misconception, in a hunter-gatherer state of nature teenagers are naturally dependent on their parents until their late teens) requires more parenting effort from the parents than they are able to provide for themselves, so older lifespans evolved so that grandma's could assist with the rearing and providing of the children. These grandparents contribute more calories than they consume right up until they die (i.e. retirement is a modern invention that is not natural).

This theory is referred to as the "grandmother hypothesis." So, next time grandma flies out to help out with a newborn, remember that that is why you can expect to live beyond menopause.