That was once a common sense idea but it isn’t true for the most part. Or, I should say, it describes what happens during aging but not why. I, and several others, gave examples of animals that are closely related and of similar size but still have very different lifespans that are immutable by any current technology. There are almost certainly several different major causes of aging but body mass or complexity don’t appear to be among those.
That’s way too simplistic. Behaviour after reproductive age can easily be a factor.
A genetic trait that results in parental nurture of offspring (even after cessation of parental reproduction) could be an advantage, and selection of that trait would preserve the genetic basis of it.
Similarly, a trait that results in parental competition with offspring could be negatively selected - and the genetic basis of it could be discarded (by the very action of the non-reproductive parents).
Evolution doesn’t even care if individuals breed at all - non-reproductive individuals can still effect an advantage to the future survival of their genes by co-operating with other individuals who share those genes - for example in a hive (worker bees contribute indirectly/non-reproductively to the future of their genetics).
There are people who survived to their 70s and 80s from the 17th and 18th century. As long as you didn’t die of physical trauma or infectious disease I would assume the normal lifespan of a human hasn’t changed much.
Which begs the question, if evolution doesn’t give a shit about us after age 45 or so, why does it take another 40 years to die? Maybe our bodies self repairing mechanisms are just extremely good by nature, but I don’t know.
Like I said - there’s an apparent evolutionary benefit to menopause. A too-old woman having a pregnancy in the days before modern medicine is much more likely to experience difficulties with the process, and especially the birth; and more likely to have a child with problems. She is consuming valuable resources, since in most societies food is a scarce resource much of the year. Unless we presume most tribes were callous enough to expel or murder pregnant grannies, a female reproductive system that does not shut down well before old age is a negative survival trait.
As mentioned, evolution does not “plan” these things. But it seems the way ovaries evolved was such that they eventually used up their pre-determined supply of eggs and shut down; therefore the women whose ovaries reached their best-before date earlier in life, once they had an decent number of offspring, were better able to provide additional child-care, food preparation, and other valuable tasks - freeing up the younger adult members of the tribe for the heavy-lifting jobs. A mother who has to take the children into the forest while looking for berries and tubers is probably more likely to lose the child one way or another, versus one where granny watches the toddler at the hut.
And obviously, the only reproductive physical stress on men is achieving orgasm - nowhere near the stress of 9 months of pregnancy and childbirth - so there was not the same selection for men to cease reproduction capability earlier.
So evolution simply accepts the mechanisms it has already created, and refines them (sometimes to absurdity, like giraffes or skunks). As age causes the various body processes to work less efficiently and eventually fail, the risks of death increase. There probably aren’t many 80-year-olds today who have not survived some form of medical intervention that would have come close to killing them - as simple as antibiotic treatment, gallstones or kidney stones; even cataracts or arthritis in prehistoric times was likely to lead to death sooner. The ones who record living to 80’s or 90’s were the lucky ones who “won the lottery”, like 100-year-olds nowadays, they managed to avoid everything from cancer to heart attacks to pneumonia. So evolution didn’t have us drop dead early because grandparents can be a survival mechanism, and so there was no selection for quickly shuffling off this mortal coil.
One thing I can say, having reached that age where the generation above me is in the Alzheimer’s and elder care stage… I have noticed that once something significant happens - a major illness, cancer, hip replacement due to fall, etc. - it seems a person who was getting along fine for years suddenly turns a corner and does not survive another year. Avoid that major trauma and you are the lucky ones who live to 90 and beyond.
The evolutionary effects of birth control?
Yes, above a certain age, it is much harder to recover from illness, so a cold that a 40 year old can suffer through or knock down for a week with antibiotics may kill an 80 year old with the same antibiotics and care.
My aunt was struggling along with failing kidneys (after a lifetime of bad kidneys from an early infection), recovering from heart bypass (decades of smoking), and even had a stroke (from blood thinners for the heart disease). She was ambulatory and had good spirits and was determined to get better, waiting on transplant. She finally got called up for transplant surgery, but complications from the surgery knocked her bad. First was a rough surgery, then digestion troubles, then the kidney went bad. She was down for 2 months bedridden, which on her already weak and small frame meant she was a skeleton. She went into a nursing home for long term rehabilitation to try to recover mobility, then did something stupid and fell and busted her hip. That ended her will to live. She was 68.
It did change. Perception of how old people lived in the past is skewed because those we remember are those who lived long enough to become famous. You have clearly in mind the king who had a 30 years long reign, but don’t pay attention to the other who died at 28 after a 2 years reign. The officer who died a captain at 30 is unknown, while the other who lived long enough to become general and win a battle is remembered. Same with people who died too early to become a president or a famous author or to make a scientific discovery, and so on…
Besides physical trauma and infections, plenty of diseases or their complications were untreated until the 20th century. Heart issue meant death. Appendicitis meant death. Heck, even a toothache could mean death. And of course giving birth was a high risk operation for women. And infectious diseases, that you mention, were of course much more widespread and lethal. Physical trauma also was poorly treated, in fact. Plus add poor hygiene, poor nutrition (complete lack of nutrition sometimes, even : starving to death was a real possibility), and on top of it much harder work that would take its toll on the body.
As I mentioned many times, I calculated he average lifespan of the kings of France and England between 1000 and 1500, excluding thoses who died violently and the one who died in infancy. French kings during this period lived on average to their late 40s, and only one in 500 years made it to 60. English kings did a bit better, and lived on average to their early 50s, with IIRC 2 or 3 living to be 60.
That (late 40s-early 50s), is in my opinion much closer to the actual life expectancy of people who lived past childhood than 70 or 80. Yes, there would be people who lived to be 70 or 80, the body can hold that long, back then like now. There were people who lived to be 90 or 100, even. But that wouldn’t be the norm, not because the body couldn’t but because there were many ways to die early.
(And in fact, 70 years was the life expectancy of a man when I was a kid. We gained about 2-3 months/year during the last 40 years alone. So living to be 70 wasn’t the norm even in the mid 20th century in the industrialized world).
clairobscur, you are confusing “life expectancy” with “life span”.
“Life expectancy” takes into consideration all causes of death. All of those things you mention are ways people die. What that means is the vast majority of people died at an earlier age than now.
“Life span”, on the other hand, is a look at how long the human body will function before it falls apart. It is how the body wears out due to ceasing to function. The oldest humans are 120 - very very few make it over 100, a small percentage make it over 90.
The percentages have gone up, but there were people who lived to 100 centuries ago. A lot fewer of them, but some.
The aging question is as much about the life span as it is life expectancy. If we could recreate negligible senescence in humans, you’d still have to worry about getting hit by a bus, or coming down with an infection, or being born with diabetes.
Precisely. Life is a lottery. Peopled died earlier because there were so many more things to die from, not because the body did not last as long (if they at that time avoided the traumas we can now cure).
Ramesses II for example, live to 90 or 91 years old. Tut died of an infection before he was 20.
OTOH, Henry II died of a bleeding ulcer; his son John I from dysentery. (Richard the Lionheart died of gangrene from a crossbow through the arm, walking too close to a castle he had under siege). John’s son Henry III died of an illness in his 60’s. His son Edward I died of dysentery at 68.
I suppose we could make a list - George I died of a stroke at 67, and so on. The point is, death was easier to come by but there’s no indication that, absent these problems, and given good nutrition (another challenge in bygone times) someone could not enjoy the same lifespan as today. Most of these problems are now curable or treatable. (stroke is often is a side effect of treatable high blood pressure)
There’s the old story that the image of the “witch” as old crone comes from an accident of evolution; women, due to the risks of childbirth, tend to have somewhat stronger immune systems; and also tend to have less issues with heart attacks and similar health issues. So, a woman who survived to menopause had a good chance of surviving her husband, and possibly her children, possibly to become a reclusive old lady with no contemporaries left alive.