
Fertility Is Kaput, but Life Goes On - forloop
http://joshmitteldorf.scienceblog.com/2015/03/30/fertility-is-kaput-but-life-goes-on/
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cauterized
It's also worth noting that reproduction is more taxing and more dangerous for
human women than for the females of essentially any other mammal (perhaps even
any other vertebrate?) species. Additionally, we have a longer period of
immaturity than virtually any other animal species.

A woman who ceases to bear children [let's say at age 45] while she still has
15 years of vigorous healthy life ahead of her is more likely to be alive and
healthy to raise her last infant to adulthood because a) she's less likely to
die in childbirth and b) she won't be weakened and spend resources on further
pregnancies -- which helps ensure that the immense investment she's made in
the earlier children will pay off.

Now image her counterpart who continues to be fertile after age 45 but will
keel over the minute she hits 60. What if her next pregnancy after 45 kills
her and leaves all her youngest children (say, ages 1-10) without a mother?
That hurts their chances of survival and of the fitness and health that would
make them desirable reproductive partners. And if she does survive all her
following pregnancies? She's leaving behind several young, motherless children
(perhaps even a newborn) who also don't have a great chance in the world.

What, their siblings will help raise them? But that decreases the resources
available to the elder siblings' children -- the next generation -- and
jeopardizes their fitness too.

Human reproduction is unusually resource intensive and errs on the side of
investing more in a few high quality offspring rather than having hundreds
(think tadpoles) of which only a few survive to maturity. Resources in terms
of all of the energy and nutrients the mother gives the fetus, and resources
in terms of years of teaching and socialization and investment in developing
the brain. You basically can't _have_ what we'd consider a functional adult
human without that huge investment of resources.

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ArkyBeagle
The main span of human existence was principally tribal. If the mother died (
and just projecting back from 19th century death in childbirth rates ... ) the
tribe raised the kid.

The tribe mainly raised the child anyway past a point.

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TheEzEzz
I like the idea, but it's difficult for me to swallow the group selection
pill. If everyone else in my tribe has this population control gene but me
then I benefit greatly because I'll have many more children without the tribe
becoming overpopulated. Eventually my gene out competes the communal gene and
the entire tribe overpopulates and collapses. Why doesn't this happen more
often? What mechanism exists to prevent me from having this mutation? If I
have this mutation am I essentially a cancer on the tribe from which the tribe
cannot recover? This doesn't seem like the dynamics we observe in nature.

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pingou
I don't know anything about the subject but still feel like it's a strange
explanation.

To me it seems like it would be a great advantage for the species if you could
reproduce past the normal reproduction age, if you made it this far it
probably means that you are perfectly adapted to your environment.

What about the depletion of resources? I imagine it must have been pretty rare
for an animal to be able to survive past the end of his reproductive years,
and unless you live in an island I had the impression resources shouldn't be
an insurmountable problem.

And if it is, then I guess a big part of your population die, but the other
recovers as there are less mouths to feed, and it's still an advantage to be
able to reproduce when you're old.

Again, I don't know anything about the subject, and like the author, I'm not
that convinced about the Grandma Hypothesis either.

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tsotha
I think it's unlikely given the length of time people actually lived before
civilization. More likely there's just no evolutionary advantage in female
fertility after age 40 - she starts having children at 14 or 15 and has one a
year until she dies in childbirth. She never makes it to middle age.

Why accept there's no advantage in other age-related breakdown (like arthritis
or failing eyesight) and expect there's some grand evolutionary plan in
fertility loss?

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bunkydoo
This is interesting. I have wondered for quite some time now if the millennial
generation will be subject to mass infertility in their 30's due to constant
cell phone radiation near the genitals. Obviously this won't be the end of the
world, but it may certainly cause a drop in planned pregnancy. Fertility drugs
are typically seen as rolling the dice, so maybe adoption will become the way
of the future - who knows?

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irishcoffee
N = 1 sample size:

I'm almost 30, been carrying a cell phone since I was 16. The mother of my
child, same thing. At the time of conception (we were both mid-late 20's), we
were drinking like fish, smoking a half pack a day, eating horribly, for
whatever reason we were both in great shape (I exercise a lot, she was very
into dancing), using protection (not as well as we thought apparently) and
bam, shes pregnant.

There was a list on thebump.com or some such website, listing all the do's and
don'ts for getting pregnant, we pretty much broke every rule both ways,
weren't trying, and now we have a child.

I think the bigger problem with fertility will be overweight/obese people more
than anything else. I have friends who have been trying to months/years, no
luck. There seems to be a strong correlation between weight and fertility, at
least in my anecdotal experience.

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joshuapants
> I think the bigger problem with fertility will be overweight/obese people
> more than anything else

Obesity is linked with low testosterone in men, and normal levels of
testosterone are necessary for good sperm production and fertility
(testosterone treatments have the opposite effect) so I think this is correct.

