Common Alzheimer's Disease Gene May Have Helped Our Ancestors Have More Kids (science.org) 40
Science magazine reports:
Roughly one in five people are born with at least one copy of a gene variant called APOE4 that makes them more prone to heart disease and Alzheimer's disease in old age. That the variant is so common poses an evolutionary mystery: If it decreases our fitness, why hasn't APOE4 been purged from the human population over time?
Now, a study of nearly 800 women in a traditional society in the Amazon finds that those with the disease-promoting variant had slightly more children. Such a fertility benefit may have allowed the gene to persist during human evolution despite its harmful effects for older people today...
The Tsimané data also allowed the team to home in on how APOE4 may boost fertility: Women carrying it were slightly heavier that those without it, started bearing children about 1 year earlier, and had their next child a few months sooner. That fits with being more resistant to parasites, says siological anthropologist Benjamin Trumble . "Being in a better immune state means that you can then devote more calories towards growing faster, and then you're able to reproduce faster."
Thanks to Slashdot reader sciencehabit for sharing the article.
Now, a study of nearly 800 women in a traditional society in the Amazon finds that those with the disease-promoting variant had slightly more children. Such a fertility benefit may have allowed the gene to persist during human evolution despite its harmful effects for older people today...
The Tsimané data also allowed the team to home in on how APOE4 may boost fertility: Women carrying it were slightly heavier that those without it, started bearing children about 1 year earlier, and had their next child a few months sooner. That fits with being more resistant to parasites, says siological anthropologist Benjamin Trumble . "Being in a better immune state means that you can then devote more calories towards growing faster, and then you're able to reproduce faster."
Thanks to Slashdot reader sciencehabit for sharing the article.
Why hasn't the gene been purged? (Score:5, Insightful)
Re:Why hasn't the gene been purged? (Score:4, Insightful)
Agreed. Natural selection facilitates evolution by weeding out via failure to procreate before death. Unless I'm missing something, this article is posing a silly question.
Re:Why hasn't the gene been purged? (Score:4, Insightful)
Just procreating isn't enough. Your kids have to survive and procreate themselves.
For several species (elephants, orcas, and humans) reproductive success is enhanced by surviving grandparents, especially maternal grandmothers.
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Correct, but grandmothers used to be 40 or 50, not 60 or 80 and even so, when Alzheimer’s sets in it’s often not to the detriment of anyone, it’s a rather gradual disease, so having someone who occasionally forgets something taking care of a child may increase social cohesion and even make the kid more self sufficient and as they get to be teenagers and grandma becomes less self sufficient, it creates an opportunity for them to learn about caring for others before they themselves have a ch
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If there is one thing that makes a woman attractive, it's a lack of parasites.
Re:Why hasn't the gene been purged? (Score:5, Insightful)
It's pointing to ONE gene associated with Alzheimers that there is an odd correlation to having more children. However today we know of at least 70 genes associated with Alzheimer's, and there may be more. Our understanding of the human genome is actually quite primitive when you look at the research; there's a whole lot more going on.
More importantly, perhaps that gene serves an important function in early development or youth. The genome is vastly more complicated in that "X gene has Y function", like that gene causes Alzheimer's. Rather a gene or combination of genes provide a purpose for a living organism, but that purpose also has context. Perhaps it's functional purpose is important at a younger age, but as someone gets older that context is not only no longer relevant but that function is in fact detrimental.
Given that most living organisms are optimized to grow up and spread their genes through reproduction, then a gene sticking around causing a problem for an organism well past it's prime (like humans) has no evolutionary basis to be removed or not. Per nature, if you're older you're now food for the younger, more fit organisms out there; hell in fact Alzheimer's would in fact slow you down and make you more viable food for a predator leaving the younger humans more opportunity to pass on their genes.
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It wouldn't... that's the point. That is what is obvious.
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If you have a gene for Alzheimer's, you still may pass on your genes because it doesn't affect you when you're younger and able to spread your genes. It only affects you when you're older. You don't suddenly get a gene when you're older and not pass it on; you had the gene when younger. Nature only purges genes that are detrimental to passing on more genes. Alzheimer's associated genes are not detrimental to that, and in fact may serve a purpose when yo
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I can just see the next headline: "Research shows Alzheimer's patients tastier to mammalian predators."
Re:Why hasn't the gene been purged? (Score:4, Insightful)
Seems pretty obvious to me. Both Alzheimer's and heart disease are largely diseases of old folks well beyond their reproductive prime.
I don't think heart disease was very common before modern life, so not a lot of evolutionary pressure there.
As for Alzheimers, the idea that old folks are out of the natural selection game doesn't really hold up. For instance, women literally evolved the capability to stop having children at a certain age. This only makes sense if there's a continued evolutionary benefit to women living well beyond their reproductive years [wikipedia.org].
So an elder is still able to contribute to the success of their offspring (and the genes of the tribe in general), meaning these is evolutionary pressure against Alzheimers.
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Female primate reproductive systems come preloaded with a bunch of eggs and they are continuously culled as you get older. From millions at birth to less that 300k by the time a woman is 30. Menopause is a shutdown of systems no longer needed because there are no more eggs to fertilize. Any utility beyond that would be in assisting in the 3rd generation's childrearing, but as more bodily systems approach failure and the 3rd generation grows up that becomes less and less necessary. Which means family units w
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if there's a continued evolutionary benefit to women living well beyond their reproductive years
The Grandmother Hypothesis. Help to raise the kids. Not the senile old bat that we have to keep from wandering off into the jungle.
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There is a 'grandparent' effect - having an extra adult around to help rear children, gather food, and share experience across generational barriers is obviously beneficial to survival of the genetic line in a cooperative social species.
That assumes there is a long enough period of health before the elderly person requires more support from the group than they are providing in productivity, but with humans even without modern healthcare we can live long enough to see two additional generations reach adultho
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As you point out, in the old days, people could live old enough to see their children and grandchildren become adults. That could easily happen by 45 if each new generation is born to 15 year old parents, which was probably pretty common hundreds or more years ago.
So at 30, you could be a grandparent. Clearly at 30 you are doing just fine if you don't catch some nasty virus or disease.
Alzheimer's is for ANCIENT people at this point. By the time your 61, your child is 46, grandchild 31, great grandchild is 1
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Seems to me anything that kills you quicker after you have reached an age where you are no longer fit enough to be a provider nor fit enough to be childcare for the providers is probable a net benefit to the group (even today). And I say that as someone fast approaching that age.
Re: Why hasn't the gene been purged? (Score:1)
So they forgot they had kids and had more? (Score:3)
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Beat me to it. Was the first thing I thought of, which I guess is a good thing. We're not suffering yet.
Not sure how anyone could forget their kids. My wallet reminds me every hour.
The real reason (Score:2)
Junk Science (Score:2)
Re:Junk Science (Score:4, Insightful)
Under most circumstances, there is DEFINITELY evolutionary pressure to promote survival after the reproductive years in humans.
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> At least for the past several 10 thousand years, thereâ(TM)s been a well-documented âoegrandparent advantageâ.
Indeed! Older people were "the internet" of the time, because they saw and lived much. They could also babysit the brats even if they couldn't farm or hunt much. And believe me, if you don't watch kids closely, bad shit happens.
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Another junk study instead of real science (Score:2, Interesting)
Just statistics, and correlation-causation presumptions.
Consider: "...gene variant called APOE4 that makes them more prone to heart disease and Alzheimer's disease in old age". HOW does this gene variant actually have this effect? If we KNOW with certainty exactly what the mechanism is, then it would not simply make one "more prone"; that's an idea derived from seeing a correlation but not knowing the details and therefore not being able to be 100% accurate in predicting a result of the presence of the vari
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Just statistics, and correlation-causation presumptions.
Consider: "...gene variant called APOE4 that makes them more prone to heart disease and Alzheimer's disease in old age". HOW does this gene variant actually have this effect?
That's... not the point of the study. That's just background info from the introduction.
If you think the association is bogus then take it up with one of the five studies they cited in support of that fact, but I'm not sure why you're going on about it for this study. I mean the associated is so well documented it's mentioned in the wikipedia page [wikipedia.org].
So, we have a "study" or "studies" that seem to show a correlation between the gene variant and one set of issues, and somebody then does another "study" of 800 women and an uptick in number of children is noticed. Underlying mechanism? No clue.
Did you even read the summary before going on your rant?
Women carrying it were slightly heavier that those without it, started bearing children about 1 year earli
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This correlation will cause other studies to look for the mechanism. I bet the study authors wished themselves to uncover the mechanism, but their funding only covered what they did. Same for the range of study subjects. More studies will be done on your dream populations in Norway or Japan.
And in a few years we will understand the mechanism, too.
The "pesky" immune system (Score:2)
Yes, it is speculative and states so. Nothing wrong with that.
In general there's a lot of trade-offs with immune systems. Alzheimer's appears to be the immune system gone wrong, attacking things it shouldn't. An aggressive immune system may help younger people avoid body damage from the parasites mentioned in the article. But this mechanism often "eats the brain" in the elderly.
Annoying allergies are another form of immune-system attacking the wrong things. There's evidence being around farm animals and pet
Nature doesn't care about the old (Score:2)
Nature only cares that you live long enough to have, nurture and launch the next generation.
Experiments have shown that lifespan can be easily increased, if you actually select for it.
Understand the "selfish" in the The Selfish Gene (Score:3)
You could see the genes as a the way for organisms to make more copies of themselves in the next generation. But you could also see the organisms as mere means of genes making more copies of themselves in the next generation
Of course it is a stretch to attribute motive, planning and action to something so inanimate as a section of a long molecule. So it takes a whole book to explain how it could appear as though they do.
Crux of the solution is, not all organisms make perfect copies of themselves,. Those who do, the ones using asexual reproduction, are not the real dominant ones. But genes that survive pass on unchanged and survive in the next generation. Since we see genes that have survived for millions of years, we need to conclude, yes it is the genes that are selfish, the organisms they manipulate are simple expendable by product.
Seen from this point of view, the selfish gene does not care the organisms they create and manipulate suffer dementia or live in constant fear of predators or they die painful death...
From gene point of view, they dont care. If they are offered a choice, more copies of yourself in the next generation, in exchange of heart breaking diseases for the organisms in the old age. They will opt to make us all suffer horrible diseases in the old age.
The genes are selfish. We are mere carriers to be used and discarded.
It's not negative (Score:2)
"If it decreases our fitness, why hasn't APOE4 been purged from the human population over time?"
They can get kids and grand-kids and then they die, a benefit for the tribe, not having to feed unproductive old people.
You can help! Click daily! (Score:1)