The grandma hypothesis — why does menopause exist?
Jan 2023
Humans have a very strange life structure compared to other primates and animals. We give birth to few offspring that have extremely high energy requirements (in terms of time and energy dedicated to their care), we have much longer-than-average post-reproductive periods, and we live very long lifespans overall.
Why is this the case, when most other species, especially those phylogenetically closest to us, have proportionally much longer active reproductive periods where females continually give birth until near the end of their lives? Anthropologists believe that the answer to this question lies with the development of food sharing and social behaviors.
In prehistoric hunter-gatherer tribes, generally males spent most of their time hunting or scavenging for sources of animal protein. However, the rate at which hunters brought back a catch was highly unreliable, so females looked for root vegetables, fruits, seeds, and other sources of fats and carbohydrates to use as fuel in times of scarcity.
The question was, when a group came back from a successful hunt, who got to eat the catch? The answer depended on a particular set of social dynamics evolved from two factors: firstly, that hunting in groups of men increased chances of success, and secondly, the very same lack of reliability, because it meant that the entire population then had to live on whatever any member could find. In other words, pooling together resources was beneficial for overall group survival.
Therefore, sharing became a key part of early human evolution. If, then, every member’s contribution was valuable to the group, including that of the gatherers, it so follows that nature would select for humans with greater understanding of where and how to find those sources of fuel to supplement successful hunts. Such an understanding is developed with practice, over time, because it requires an incredible amount of knowledge.
For example, to find tubers, the primary source of carbohydrates, one needed to tell apart soil types, the different leaves identifying edible tuber species, the bump shapes that determine how big the tuber is beneath the ground, the particular sound made by tapping on the soil that reveals the ripeness of the tuber, etc. It makes sense, then, that older members of the group, the ones with the most experience, were actively contributing to overall wellbeing well until their final years, even long after they weren’t having children, or were in menopause. Their roles were caring for the children, helping with food provisioning, and teaching the new generations the secrets of the gathering trade.
Grandmothers today are known for their wisdom, especially when it comes to cooking and taking care of kids. For our ancestors, it was no different.