Preparing for evolution.  One reaction to the news that any species that becomes and remains a single large randomly mating gene pool will probably go extinct is, “How horrible!  That’s so inconvenient.

Say a developer decides to make money by building a high rise condominium.  He will get in trouble if he does not take into account the possibility that nobody will want to live there.  We are seeing that happening.  Throughout the developed world people have built more houses and condominiums than there are people who need and can afford places to stay.  The result of course is a catastrophic and worldwide fall in prices.

At first glance, this should not be a problem.  People who need places can get them cheaply.  People who have a place to stay will be selling at low prices and buying at low prices, so that should be a wash.  In fact, their property taxes will be lower in the end than they would be if the market were high.  But the problem is that people have bought houses and condominiums they never expected to use.  They bought them at high prices expecting the prices to continue up.  They are now poorer, so we are all poorer.  In short, the resources that went into the new buildings were squandered, and we must all pay for the folly.

(There are other problems of course, including people who need to sell homes now too big for the remaining family to finance retirement, people who need to borrow against equity and people whose mortgages are now more than the price of the home, but these are outside the current subject.)

Suppose we had all been making prudent choices.  Suppose things were such that property values were fairly stable.  Then the developers could reasonably expect that their new construction would be purchased and people would move in as local jobs became available or as people accumulated enough wealth to buy more spacious homes. 

And now suddenly somebody says, “Wait.  You can’t just move anywhere there is an opportunity to work and buy a new house.  You need to stay where you are (or go where your ancestors were) to keep your community intact.”  And suppose the warning is heeded.  Now the question is not can you build but whether anybody would move in even if they could.  You would just about have to line up a community and say, “If you will go in with me on this, I build the houses and you all move together.”  That is far more difficult.

In fact, I have seen it done more or less.  In Sweden I once had friends in a subdivision who all seemed to know each other and had known each other since childhood even though the houses were new.  It turned out they had all grown up in the same neighborhood.  When they were all rich enough to move into newer homes, they all moved to the new neighborhood at the same time.

So yes, in that sense it is inconvenient.

But the clamor of complaint goes on.  What about globalization?  What about recruiting skilled people from abroad who want to move here?  What about the fundamental fragmentation of or society?  Yes again, those are legitimate issues.  But they need to be addressed if we want to have babies. 

Nobody ever said babies were cheap.

What about going extinct?  That would be bad.

Yes, it would be bad but it can be avoided if we understand the threat and make prudent decisions.

Why did nature do this to us?

Myself, I don’t see how that could ever have been possible.  We are stuck with the fact that there are chromosomes, and we are stuck with the fact that any mechanism, (anybody who as ever cleaned a fish knows that a body is a mechanism, with tubes and pumps and levers and cables or the equivalent) must be fine tuned.  Otherwise it would be like building a car and suddenly coming up with a bigger better wheel.  The wheel well will need to be adjusted accordingly.  So this happened because really there was no alternative.

But even if there were an alternative, it would never have happened any other way.

That is because there is a subtle advantage to subdividing a population to restrict gene pool size.  With the population already subdivided, a species is in an ideal position to exploit a new environmental niche if one should turn up.  The new opportunity could be exploited by a single sub group without requiring the bulk of the species to make changes that might render them less adapted to the niche that is already being enjoyed. 

Think about it.  Say there is a big island on which there are rabbits, and there are two predators, dogs and cats.  And for the sake of argument, say the cats are all one big randomly mating gene pool while the dogs are forced by the kind of genetic pattern we have described to divide into different breeds.  Now a new opportunity arises.  Deer move in and compete with the rabbits and also offer another food supply. 

The cats may have a chance to take down smaller deer, but even working together would have no chance with grown ones.  The dogs have the same problem.  Now both the dogs and the cats get a little bigger, compromising between the ideal size for a rabbit and still being able to take down some deer.  But now one of the dog subpopulations begins to get very large indeed.  They are the ideal size for deer and quite unsuited for rabbits.  The deer are now being optimally harvested, so the other breeds of dog return to the small size appropriate to rabbits. 

Now the rabbits are being optimally harvested, too.  The cats, in their compromise, have no niche.  The cats die out.  Or else they optimize to feed on deer and compete on a level field for the deer or optimize for rabbits and still survive there.  Then either the deer or the rabbits go extinct.  If the cats have been depending on the species that went extinct, it is the end of cats on that island.  The dogs may loose some breeds, but there will still be dogs.

So in the long run, nature will always favor the population that automatically subdivides.  Even if there were a way to manage a very large gene pool, we would be surprised to find one.

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