It might have been a mere speculation but it kind of makes sense.
Rather than take the time to bare and raise one child, that time is better spent taking care of your 6 grand children.
* Women stop having children after 40 because it's more important to raise the children you already have. * Women don't stop having children after 40 because bearing more offspring increases your chances of survival.
Your explanation barely makes sense even on its own merits. Surely, if nature wanted us to have N children and then take care of them, it would have set a cutoff on N, rather than on the time. What if someone has no children before 40? Is it to their evolutionary advantage to care for the children they didn't have?
Or, if your explanation were true, why would women not spend ten years gestating and given birth to a healthy 10-year old? It's illogical to design a system that can pop out one baby every nine months and then say "okay now that you've had anywhere from zero to thirty children, it would be best if you stopped and took care of them.
To design? Are you a creationist?
Assuming you're just confused, evolution doesn't "design" life. It's just a "whatever works" process.
For example, angler fish have a lure that resembles prey for their prey. This has been selected by the eyes of their prey. It's not that the prey wanted their predator to fool them, it's just that angler fish with bad lures starved and died off.
In the case of humans, if what your parent comment suggests is true, then it would just be that some women had some sort of defect where they couldn't give birth after some point and that turned out to give their grandchildren an advantage over the grandchildren of women without the defect. Over a long period of time, more and more descendants with defective reproduction genetics would survive compared to those without and so it becomes prevalent.
That's how evolution works.
Put it another way, if I asked you "would you think that evolution would select for women bearing children until their 40s, or until they died?", you wouldn't be able to answer, because there's no predictive power in the explanation. Contrast this with "the sun rises every day because the earth revolves around itself", which allows you to predict whether the sun will rise or not tomorrow.
I agree, that's what I said "if what your parent comment suggests is true"
In fact, said parent comment said "It might have been a mere speculation but it kind of makes sense"
I agree with you that there is no predictive power in explaining things that way (indeed, what I said is speculation, hence why I worded it in the conditional), but that was not what I was responding to. I was only responding to the "design" part of your comment.
That being said, evolution does make predictions which have been confirmed. Notably Darwin's long-nosed moth. Here's a list of more predictions[1]
Well, I would argue that the vibe of your whole comment was coherent in that sense: you talked about what nature wanted, about design and about what kind of stuff would make sense while looking at it from a architect perspective.
It's a very odd way to look at it if you have no creationist conception of it all to be honest.
As for your point that not everything has an evolutionary advantage, I agree. Deafness and blindness exist after all.
But I don't really see your point as far as proposing hypotheses to account for certain prevalent traits, which, in my opinion, is what the original content was about (the grandmother hypothesis).
To talk about what nature "wants" is probably not very helpful. I can't speak for the idea that menopause exists because it is useful for old women nurture their grandchildren, but tendencies like it exist simply because they are helpful enough in an evolutionary sense.
I mean, why should we want to have sex without reproducing? If nature "wanted" us to have children, why not make that coincide exactly with our sex drive? It's because no one designs these things or thinks of logical solutions. Having a sex drive regardless of individually wanting to have children works to a genetically beneficial end either way.
> Is it to their evolutionary advantage to care for the children they didn't have?
Their evolutionary advantage? How can an individual gain an evolutionary advantage in itself? When I'm dead, I'm dead. Nothing can be an advantage or a disadvantage to me as an individual at that point. The process of evolution stretches across generations and concerns things that do sustain for several generations, like genes.
Why would a spider want to mate if it almost always gets eaten immediately after doing so? How is it to their individual advantage to be eaten? Why would bees be born without reproductive capabilities? It's because these are genetically beneficial traits, not because the individuals themselves will gain from it.
Exactly. The most we can say is "it's generally useful so it tends to happen". However, evolutionary biologists tend to paint their explanations with a certainty that just isn't there, and can look at any old random thing and say "well, this is obviously because X!".
"Evolution made spiders eat their mates because it makes sense that they would want to preserve energy". Yes, but it also makes sense that the mates would stick around to feed the offspring, otherwise all species would kill the males after mating. We aren't as sure about why things are the way they are as evobio would have us believe, and not to mention evobio explanations for human psychology, which are usually completely ludicrous.
In general, the process for explaining things using evolutionary biology seems to be:
* Look at behaviour.
* Find one advantage, however small, of said behaviour, regardless of disadvantages.
* Say "well obviously this behaviour evolved like this because of that advantage".
* Publish.