(Simon, this is me mostly responding to the people above you. :] )
I hate the grandmother hypothesis. It is one of my least favorite evolutionary theories, and every time it comes up in class I just have to get argumentative. So here’s why I dislike the grandmother hypothesis. It could be right, but I don’t think it is ‘cause it makes a couple of leaps of logic that we simply have no proof for. So here’s why I dislike it and why I think it is, at best, only partially correct.
1, It’s sexist. It was conceived in the 50s and 60s, a time when primarily male biologists and anthropologists very much were assuming gender roles always have been what they were in these mens’ time. There is no proof that this is the case (those with a uterus obviously have always been the ones who give birth, but the responsibility of childcare varies widely from culture to culture and we have no evidence of gender roles - or even evidence of gender at all - in early hominins when this would have been evolving.), as culture doesn’t survive fossilization and gender is cultural. It’s both naive and intellectually dishonest to make that assumption. Especially given that there’s evidence that women have always been more integral to food production and procurement than men (at least in hunter-gatherer societies and societies recently enough deceased for some culture to survive.). The grandmother hypothesis was and is deeply influenced by the cultural attitudes of them men who came up with it because they couldn’t conceive of a “use” for women past child-related functionality. Of course there’s likely always been some kind of division of labor, but evidence that correlates with gender grows thinner and thinner the further back you go and there’s absolutely no reason to think that men couldn’t have been considered equally important to child rearing. But I’ve read enough work from the time period to know that it never even entered the mind of male scientists that men assisted in child rearing. Their culture influenced their scientific work. They just didn’t see women.
2. It asks the wrong question. The question SHOULD be, why are humans so long lived, in general? Humans are the longest lived land mammal. The only ones that come close are some other primates that are kept in captivity. Many men are impotent, but no theory is necessary to explain why they are “allowed” by nature to live past their usefulness in breeding because men are assumed to have more than one, singular use. If the male role in hunter/gatherer is assumed to be hunter (which I don’t personally assume, but for argument’s sake.), then their usefulness comes to an end when they grow too old to effectively hunt (especially for a pursuit predator - although early anatomically modern humans used a variety of hunting techniques. My favorite of which is chasing large animals off cliffs and collecting their corpses at the bottom.), but no one asks “why do men live past their usefulness” because they are assumed to have other uses. Actually, elderly humans don’t have a whole lot of physical uses when it comes to the evolutionary necessities of procuring food and breeding. But they do have one really important use, and it’s all related to that damned big brain of ours. The elderly know things. For a species whose survival and evolution was almost entirely dependent on our social groupings, social bonding, and ability to use tools and solve puzzles, the elderly are an indispensable social and intellectual resource. They also are a good resource to handle tasks that aren’t physically intense - and that doesn’t necessarily include child rearing. Child rearing is, or definitely can be, physically intense. They also are important in community organization and social bonding - cornerstones of human evolution and even modern human societies.
3. If the real question here isn’t “why do women live past menopause” but “why are humans so long lived”, then an additional question would be “why do female humans cease fertility so early in their lifespans?”. Well, the answer might be pretty easy: metabolism. For a very long time, the size of a baby was thought to be limited by the size of the mother’s pelvis - something that can only get so big in a habitually bipedal species. So the theory went that being bipedal made our babies come out “undercooked”. However, recent theory suggests that it’s actually due to the mother’s metabolism and NOT the birth canal or pelvis size. Now, if that’s correct, then it makes sense for a metabolically slowing human to lose the ability to do something that’s such a heavy metabolic load. Making sperm and ejaculating isn’t a tax on the body, but growing a baby is. To me, from a biologic POV, this makes a LOT more sense than “they live long to take care of the babies”. And, we must assume that men and women live approximately equal lifespans (when social factors as controlled for - like men not liking to seek medical treatment and being socially expected to engage in risk-taking behavior.) because that’s the lifespan of the species. It makes no sense to, in humans, ask why the females don’t die off halfway through our average lifespan. We just don’t have the kind of drastic sexual dimorphism necessary to justify that kind of difference. Humans aren’t angler fish or spiders or praying mantises. Our sexual dimorphism just isn’t that pronounced.
4. It completely ignores the biological presence of LGBT individuals. Same-sex sexual relationships are found in almost every species, which suggests some kind of evolutionary purpose to them. Let’s say that proponents of the grandmother hypothesis are correct, and child-rearing plays a role in the extended lifespan. They’re STILL wrong to assume it is gender-based or sex-based. Enter the “gay uncle theory”. Which…I’ll just let you guys go read the article, because it talks about gender swapping to fill required roles and no-binary genders and altruism in kin groups. So if all of these grandmothers are taking care of the kids, why evolve same-sex partnerships and same-sex behaviors?
Anyway this is why I dislike the grandmother hypothesis thanks for coming to my Ted Talk. Always question this kind of stuff, because a LOT of what is considered to be settled evolutionary science relies heavily on gender-based division of labor that was assumed by those who wrote it - almost entirely men - and probably wasn’t correct (ex - stone tools are often assumed to be made by men, but that’s actually probably not correct. One of my profs pissed off a whoooole lot of male scientists by presenting them with both qualitative and quantitative evidence that in some modern stone tool users it’s entirely women who procure and make the tools.).
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