So the article and paper seem to be arguing that a low frequency of late-acting genes indicates ongoing evolution, but acknowledge that this raises questions about why natural selection would act on them.
The relevance of the decrease of the prevalence of these genes with age is apparently that survivorship bias is being used to distinguish causation from mere correlation.
So having healthy grandparents gives a survival advantage.
At that age, the effect should be reversed as people often need care themselves rather than caring for grandchildren (who may be adults by that time anyway)
I suppose the "grandmother theory" originally only explained why women live beyond menopause, not into their 70s, 80s or 90s.
Maybe even more importantly, though, 100 years ago other, unrelated diseases of old age were likely to get you well before Alzheimer's really got bad.
When resources get scarce, there are a lot of ugly realities.
http://newsroom.ucla.edu/stories/jared-diamond-on-aging-1505...
"Mostafavi and his colleagues tested more than 8 million common mutations, and found two that seemed to become less prevalent with age"
Old people are less likely to have this gene than young people. This can have two possible explanations: old people with this gene are more likely to are already dead (and thus not show up in the study), or the gene is becoming more prevalent in the younger generations. The statement "People without these mutations have a survival edge and are more likely to live longer" favors the first explanation.
This is not the effect of natural selection on gene prevalence. (And it would be weird for Alzheimer's, which usually occurs at an age where reproduction is often finished, and maybe even raising the kids is done already).
Note that they are not suggesting these genes have been the subject of selection; it is the hypothesized number of such late-acting genes that were not found that are assumed to have been selected against.
At least with smoking, we've been experiencing exactly that decrease for generations. Smoking has become vastly unpopular compared to how prevalent and socially accepted it used to be. Social factors had been one of the main driving forces, but that doesn't mean it has to be the only driving force.
As people live longer and safer lives, they can afford to have children later. And child mortality has been seriously reduced, so the children they have are comparable to thise among people from previous centuries who had many children younger.
Having children takes a toll on an organism, and having many children takes a larger toll, presumably. I wouldn't be surprised if there is a correlation between lifespan and number of children, among women.
So - people live longer and have children later. The children grow up richer and bigger and in turn have children later, as well.
I bet there is a correlation between age of having children and lifespan.
It stands to reason that postponing reproduction for as long as reasonably possible would contribute to selection for longevity. From evolution's perspective, you have to survive at least that long, or else you're not good for anything. If humanity collectively decides to postpone having children, evolution may begrudgingly allocate more of its resources toward the welfare of individuals, rather than viewing our early deaths as an acceptable loss in a cold utilitarian calculation about long-term gene proliferation.
(edits)
You could imagine a graph showing the percentage of pregnancies that occur at each age. The strategy would be to gradually move the percentages over time so that some percentage of sixteen year old pregnancies get shifted over into seventeen year old pregnancies, some seventeen year old pregnancies become eighteen year old pregnancies, and so on.
The goal is that, over time, there is escalating pressure to solve health problems that occur at later ages, problems that evolution currently has little incentive to address.
But dows that mean some sort of Lamarckian evolution is taking place after all?
Sexy son hypothesis is also similar. Is it related?
There is (at least for women).
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270889/
> A significant association for later maternal age was found whereby women who had their last child beyond the age of 33 years had twice the odds of survival to the top 5th percentile of survival of their birth cohorts compared to women who had their last child by age 29 (OR=2.08, 95%CI 1.13; 3.92 for age between 33 and 37 years and OR=1.92, 95% CI 1.03; 3.68 for older age).
It's important to know though that delaying childbirth among women is associated with all sorts of other "healthy" factors like high education, high income, stable marriage, etc.
https://www.ncbi.nlm.nih.gov/m/pubmed/16510865/
But this study is contradicted by many studies
https://www.scientificamerican.com/article/having-sons-can-s...
Do children at 20-30 increase or decrease life span?
Obviously people who live longer may have more children, especially the men. I am talking about the other way.
Sometimes it's good sometimes it's bad. ¯\_(ツ)_/¯
From my own observations in middle school and high school, those that mature earlier are far more likely to get into drugs, forgo education, etc... all things that are measures of success in our current society
Smart people delay, wait and then end up not... "dumb" people just hook up and go to town...
I think the fact that Evolution is still spreading "successful" genes and "unsuccessful" genes become less prevalent is obvious.
What isn't obvious, is as Idiocracy so succinctly puts it, is that gene that are "successful" doesn't necessarily translate to intelligence, good decisions, stable lifestyle, etc.
* tested more than 8 million common mutations, and found two that seemed to become less prevalent with age. A variant of the APOE gene, which is strongly linked to Alzheimer’s disease, was rarely found in women over 70. And a mutation in the CHRNA3 gene associated with heavy smoking in men petered out in the population starting in middle age. People without these mutations have a survival edge and are more likely to live longer, the researchers suggest.
* certain groups of genetic mutations, which individually would not have a measurable effect but together accounted for health threats, appeared less often in people who were expected to have long lifespans than in those who weren't. These included predispositions to asthma, high body mass index and high cholesterol.
* Most surprising, however, was the finding that sets of mutations that delay puberty and childbearing are more prevalent in long-lived people.