What is the evolutionary reason we live, on average, 40 years longer than our reproductive ability?

[justanotherneighinparadise]

I was pondering this whilst putting in my make up 🤣

If the sole reason for existence is to reproduce, why do we generally live forty years or so later than our eggs viability?

The only thing I’ve come up with is to be old enough to raise our own children to adulthood and then perhaps be the matriarch of a troop and help raise grandchildren etc?

@Sarahandduck18 it drives me mad when people misunderstood averages like this.

Human physiology hasn't changed. Many babies died in childbirth and the first few years of childhood were a big risk as well. Maternal mortality was high too and of course infections weren't treatable.
But if you were lucky and dodged all of that plus random accidents you'd still make it to old age.
Bear in mind less diseases of lifestyle too.

@Sarahandduck18

People dont understand maths!

When we say the average life expectancy was ‘40’ in medieval times it doesn’t mean people does age 40! Lots of babies didn’t make it to 1 or 5. That dramatically brings down the average life expectancy. Once people got to adulthood they would expect to live to 60+.

Older women were crucial in child rearing as younger women were out hunting and gathering (which was more divided by age than sex).

Yes, this is true. I had a discussion with someone on twitter who was adamant that a fictional character aged 82 was impossible in 1880. Several people tried to explain means to him.

When I asked my dentist why my teeth suddenly crumbled in my 40s, he said one theory is that I've done my biological job and that teeth aren't designed to last into old age.

I think we've always had the capacity to live to 70ish, it was just far less likely due to disease and no medicine up until relatively recently.

I would think that if you made it to middle age back then you'd actually fare better than the modern equivalent as less issues around T2 diabetes, high blood pressure, obesity, cancer etc.

It's not completely unheard of for grandmothers to play a role in the natural world. Orcas live in female packs and grandmothers help raise calves.

Crows have extended family networks and juvenile crows often babysit chicks for their cousins to learn how to look after young.

@Superstardjs

As pps have said, much to do with science and lifestyle. Society tends towards far gentler jobs now, so fewer deaths down the mine, on the railway etc and if you have an illness or occupational accident for example, you can be saved. I think there is also the expectation that age needs to be prolonged at all costs. You see posters on MN reporting the death of a loved one as 'too soon' or they were 'too young' but the deceased was actually in their 70s. We, rightly or wrongly, insist that life is preserved and because everyone knows someone who did yoga and rode a motorbike at 108 then old age is a marvellous thing.

Fully agree with this.

There are a few other species that have this (I think it's been seen in whales, but I could be misremembering), some support the idea that there is a benefit to having non-reproductive members caring for (alongside other social species that have members that care for the young, but don't reproduce).

Really, evolution doesn't make choices and there isn't an evolutionary reason for a lot of things. It's just what's happened and it hasn't been enough of a detriment to reproduction for it to have had much affect on us. There may be benefits, but after reproduction the risks of it don't matter nearly as much, and what happens after children are grown have even less impact.

Interesting article about it www.google.com/amp/s/www.livescience.com/amp/60587-do-animals-have-menopause.html

@MorrisZapp

When I asked my dentist why my teeth suddenly crumbled in my 40s, he said one theory is that I've done my biological job and that teeth aren't designed to last into old age.

I think this is what triggered my thought initially. I’m trying to polish a turd every morning applying my make up to a face that slowly sliding downwards wondering why we start to deteriorate so early relative to age. Like why are we living till we’re 80 but ageing relatively quickly once reproduction ceases to be feasible?

I remember reading that having grandparents greatly increased the chances of children surviving. Having older women who had stopped reproducing themselves gave an extra layer of support and protection for babies and children. The more people available to bring them up the better - and of course it meant there were very invalved women around when younger women died in childbirth.

You age visually because you don't need to waste resources attracting a mate

You live , like whales, because you are useful still

@MorrisZapp

When I asked my dentist why my teeth suddenly crumbled in my 40s, he said one theory is that I've done my biological job and that teeth aren't designed to last into old age.

Teeth didn't evolve to cope with 'unnatural' diets - be it the stone-ground flour of ancient Egyptians which wore them down, or refined sugars nowadays.

Apart from childcare, surely the evolutionary success of humans is down to our abilities to think, and to learn both from our own experience but also in a very deliberate way from other people. Older people have more accumulated wisdom. I suppose in prehistoric times (and beyond) they were humankind's 'reference library'.

It’s nothing to do with evolution, and everything to do with modern civilisation. Life expectancy in the poorest, least developed societies is decades lower than that in wealthy developed societies with advanced healthcare systems.

Life expectancy once you get over war, being a child and childbirth , could be to the 80's even hundreds of years ago (Middle Eastern scholars is one example)

We are not artificially prolonging life past 40 which some seem to be implying !

qz.com/1372767/twice-as-many-animals-go-through-menopause-as-scientists-previously-thought/#:~:text=Strangely%2C%20though%20we%20share%20this,and%20narwhals%20to%20the%20list.

Evolution does play a part.

If you think about it in the context of one family down the generations, with mothers having babies about every 2 years, the offspring are much more likely to survive to reproduce if they have a grandmother to look after them as well as a mother. So, that family would be likely to have more descendants, and pass down traits for living past menopause, than a family where the mother died soon after the youngest child was born.

If you turn it around, considering that men live to similar ages but can continue fathering children longer, there is probably an evolutionary advantage for women to have menopause well before they die, so they can look after their youngest child to adulthood with a reduced risk of dying from pregnancy or childbirth complications.

It's generally thought that it was evolutionary advantageous for women to invest their time and resources on their grandchildren rather than keep on having children of their own. Hence female fertility drops off at the age that when women would have started to become grandparents.

@Changi

People dont understand maths!

When we say the average life expectancy was ‘40’ in medieval times it doesn’t mean people does age 40

Older women were crucial in child rearing as younger women were out hunting and gathering

I think some people don't have much of a grasp of history either!

Now, now, @Changi, don’t diss those well-known medieval hunter-gatherer women.

In their crinolines. Marrying Henry VIII in their droves.

Medieval times were a particularly rough point of human history for health. The plague was a major issue because there was trade that transported rats and their fleas, and people were living in villages and towns in close proximity for disease to spread with no sanitation. Similar for the working classes in the slums of the Industral Revolution. It was worked out with mapping that cholera clusters could be linked to particular contaminated water pumps. Poor working and living conditions were idea for the spread of respiritory disease like TB.

Go back further in history to smaller communities that were far more isolated and the risks of infectious disease decrease. Childbirth has always been hazardous (although modern lifestyles don't help with some common risk factors) and the risk of infection and disability following injury.

If you can make it to the menopause in sound condition, your prognosis for reaching old age is pretty good. Men probably benefited too as younger men would do more risky physical work.

Making it to 5 years old was the biggest challenge.

A friend of mine is an anthropologist, and she makes the point that there are, in evolutionary terms, a range of strategies from "huge numbers of fertilised eggs on the river bed, leave 'em to it and some will make it due to sheer weight of numbers" through to "all your eggs in a tiny number of baskets, and hang around as a parent investing time and resources till they make it to adulthood" (many mammals, and particularly primates). The other thing is that in terms of reproductive success, you don't count number of children ('any fule' can produce loads of those, but in evolutionary terms, the ones that die before they can pass your genes on don't count) - you measure it by number of grandchildren.

So once you have an "a few eggs in one basket" strategy on the go, evolutionary pressures might select for a menopause as one physiological mechanism which meant you weren't having children late in life. But remember it's chance mutation which throws up the variation that external environmental factors then work on - so though in retrospect you can see why menopause might be useful to a species that's already gone down the 'invest a lot of your resources in a small number of children' route, but it's not an inevitable outcome or the only way evolution could have acted (AFAIK, chimps don't have a menopause for eg).

@justanotherneighinparadise

But we have the capacity to live until we’re 100 seemingly. Modern medicine and living conditions dictate that many of us are now more likely to hit old age. I just wonder what the point of it is? I can only think it must be to do with helping to raise future generations.

Almost all animals have the capacity to live longer than they do naturally 'in the wild'.

Some, we've then bred that capacity out of them by doing things like dramatically decreasing their gene pool or changing growth hormone levels to alter sizes - which then has a consequence in terms of longevity.

But in a natural genetic state, captive animals tend to outlive their wild counterparts because of access to high levels of nutrition, medicine, reduced physical stress etc.

@CaraDuneRedux

A friend of mine is an anthropologist, and she makes the point that there are, in evolutionary terms, a range of strategies from "huge numbers of fertilised eggs on the river bed, leave 'em to it and some will make it due to sheer weight of numbers" through to "all your eggs in a tiny number of baskets, and hang around as a parent investing time and resources till they make it to adulthood" (many mammals, and particularly primates). The other thing is that in terms of reproductive success, you don't count number of children ('any fule' can produce loads of those, but in evolutionary terms, the ones that die before they can pass your genes on don't count) - you measure it by number of grandchildren.

So once you have an "a few eggs in one basket" strategy on the go, evolutionary pressures might select for a menopause as one physiological mechanism which meant you weren't having children late in life. But remember it's chance mutation which throws up the variation that external environmental factors then work on - so though in retrospect you can see why menopause might be useful to a species that's already gone down the 'invest a lot of your resources in a small number of children' route, but it's not an inevitable outcome or the only way evolution could have acted (AFAIK, chimps don't have a menopause for eg).

I was wondering the same but hadn’t researched it yet. Do primates have a menopause? Other animals that live a long time, say elephants, do they have a menopause?

Because kids are useless.

If you say roughly women can reproduce to 40, at 50 they're still raising kids who aren't strong enough to take down a wooly mammoth. No, that's up to Mom and Dad whilst the grandparents do babysitting.
By 60 the kids are growing and can go get their own mammoth steak, but then THEY start procreating too. Someone's gotta hang in the cave with the kids. So that's potentially 70-75 before you've helped raise your grandkids just as your parents helped raise your kids.
Physically you don't need to be strong because your payment for babysitting is food.

@SleepingStandingUp

Because kids are useless.

If you say roughly women can reproduce to 40, at 50 they're still raising kids who aren't strong enough to take down a wooly mammoth. No, that's up to Mom and Dad whilst the grandparents do babysitting.
By 60 the kids are growing and can go get their own mammoth steak, but then THEY start procreating too. Someone's gotta hang in the cave with the kids. So that's potentially 70-75 before you've helped raise your grandkids just as your parents helped raise your kids.
Physically you don't need to be strong because your payment for babysitting is food.

And they’re ‘useless’ because the fact that we walk upright has implications for the size of the birth canal, which means that the baby’s brain has to e comparatively undeveloped to fit through — some scientists estimate that human foetuses would need to stay in the womb for 18 to 21 months to be born with brains the size of newborn chimpanzees — and because to gestate a baby for longer than nine months would compromise the mother’s ability to meet the foetus’ and her own energy needs.

Whereas foals can stand up and walk as soon as they’re born because mares are big enough and can carry foals for long enough (11-12 months’ to let them develop to that extent.