Cheaper fertility:
Medically assisted fertility has proven useful in the rich world.  There is now a move afoot ( Maybe Babies ECONOMIST vol. 412 no. 8895 July 12, 2014 page 53) to make it cheap enough to be useful elsewhere.  The article starts out with a description of a family consisting of two men and two children.  They obviously had some outside help.  This family composition might give some pause.  Are we socially sailing into uncharted territory?  Well so far as the medical side of it, yes indeed.  But I fear we have been here before.  I argue ad nauseam that departures from the old pattern of boy marries girl and they have children have been routine in among societies on the brink of annihilation.  Don’t blame the babies.  Don’t blame the surrogate parents either.  They are only a marker.  If anything, they’re a help. 

The article goes on to say that injecting the sperm directly into the egg is not necessary most of the time.  This is where my hackles rise and my nostrils dilate.  I sense data.  This, if properly collected over sufficient time, might give us another clue as to mechanism. 

You see, according to the paper I published in African Entomology, fruit flies appear to have their fertility constrained – when it is caused by lack of consanguinity – only by one or maybe more post zygotic mechanisms.  That’s technical but easily explained.  Fertility experts take the position that fertility is the norm.  When a normal male, any normal male, marries a normal female, any normal female, they ought to be able to have children.  If they do not, then one or the other of them is not normal, and treatment is reasonable. 

They divide infertility into pre-zygotic when something prevents the sperm from reaching the egg (say blocked fallopian tubes) and post-zygotic when something prevents the pregnancy from developing normally (say a genetic abnormality).  To me that presents a chicken and egg problem, which came first?  In the examples at hand, the distinction is clear.  But personally I have never managed to get married.  So I’m infertile.  Is that pre-zygotic or post? 

But when I sit down to write a computer program, the code sides with the experts, not with me.  “What’s it to be, boss?  Pre-zygotic or not?”  so I accept the opinion of experts on that one. 

In the paper I present evidence that flies have only post-zygotic infertility while mice and humans have both kinds.  And if there is one thing I do understand it is that directly injecting the sperm bypasses any pre-zygotic infertility.

When I look at the UN numbers on fertility in the world, and when I follow on Gapminder how it has evolved there seem to be both kinds of mechanism in humans.  First one mechanism causes fertility to fall below replacement level.  Then it stabilizes.  Of course it dooms us eventually, but it does stabilize.  At the moment it is stabilizing age at first marriage for women starts upward.  From that point on it never looks back.  Out of over a hundred studies for which data are offered no population having once fallen to below replacement and then experienced the rise in age at first marriage has ever seen that age turn around and go down.

In a computer model, a pure post-zygotic mechanism tends to induce a periodic fluctuation in fertility, as it appeared to do in fruit flies.  If the mechanism is pre-zygotic the fertility drops, appears to level off and then in a single generation falls to zero. 

Intuitively I would say that pre-zygotic should precede post.  So pre-zygotic infertility should run its course and then post-zygotic close in for the kill.  But that is not the way populations act.  Typically, in mice and humans, there is a surge in population, a decline and a second surge.  This is the hallmark of post-zygotic.  Then there is the terminal, unrelenting death dive, which is the sign of pre-zygotic.

So what appears to be going on is that our post-zygotic infertility has run its course and settled in for a long, genteel decline and the pre-zygotic is manifest only as that age change.

If you had asked me some time ago I would have said, “The women’s biological clocks are stopping.”  That should be post-zygotic.  But perhaps mathematically lack of getting married is a pre-zygotic situation.  The fact that I didn’t marry is pre-zygotic, not post. 

So you see it matters.  If our post-zygotic infertility has stabilized and our pre-zygotic can be technically bypassed, then maybe we have another generation or two to wake up, shake ourselves and go about rectifying matters.  But if pre-zygotic has done its worst then sperm injection can do no better than it is already doing, which is hardly sufficient in the big picture, and the cloud on the horizon is post-zygotic. 

I do not expect anybody to collect the relevant data and make it possible to figure it out unless the whole issue blows open.

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