Nine things that make things happen Part 3:
Disease affects population size if it kills people.  Population size affects disease, too.  It has long been observed that diseases are rampant in crowded circumstances.  I think rather more has been made of this than it deserves.  The failure of cities to grow by natural increase is blamed on disease, but now we have infectious disease largely under control in the cities of the rich world and the natural increase is still not there.  Let us all chant together, “It’s that thrice accurse outbreeding depression.” 

But let’s face it.  The disease most in the news nowadays is Ebola.  Thanks to the heroic efforts of Doctors Without Borders outbreaks were contained for decades as long is it was happening in little villages.  Now it’s got into cities and people, rather belatedly, are scared.  So yes, the big social pool leaves a population vulnerable to disease.

Like conflict, the fear of disease can restrict social mobility and thus exacerbate any tendency toward inbreeding depression.  There have been suggestions that inbreeding depression itself, being associated with decrease in the diversity of some of the elements of the immune system, the histocompatibility complex, so the relationship between inbreeding depression and disease is such that each makes the other worse.

As far as outbreeding depression, like conflict fear of disease might restrain the social pool and limit outbreeding.  In fact I had hitherto thought that the legendary African habit of shunning outsiders was due only to the threat of outbreeding depression.  I now must confess that it looks like fear of disease may be involved as well.

Disease and conflict have long been linked.  I think somebody has described a war in which battle deaths were for less than deaths due to disease.  The dreaded Spanish flu that took such a toll on humanity followed close on the heels of WW I, and likely the awful conditions the troops faced even after the guns fell silent contributed to the spread.  Conflict fosters disease.  If disease fosters conflict, I am not aware of it but would listen patiently to anyone who thought it did.

As far as the relationship between disease and wealth, it seems pretty obvious that they are at daggers drawn.  Malaria, that great killer, is purely a disease of poverty.  You get it from mosquito bites.  Nobody wants to be mosquito bit, malaria or no, so a wealthy society will take whatever steps are necessary to prevent that.  And modern medicine, at prodigious expense, has made significant progress in reducing the prevalence and impact of many diseases.  So wealth destroys disease. 

And of course disease destroys wealth.  Somebody has to pay for those expensive treatments, and disease reduces a person’s ability to do useful work. 

The next on the list is famine.  Famine can reduce a population in terms of a census.  That happened in China during the Great Leap Forward.  But I suspect that then as well as commonly a famine increases social pool size as people stir around and try to find a way to survive.  Also if two villages, each with its own social pool, face serious losses they might combine.  It’s difficult to say.  During the Great Leap Forward the little farming communities were terminated and the farmers forced into giant communes.  I think that was the cause of the present low birth rate in China.  People will say “one child policy,” but that was instituted only after the birth rate has fallen, and when it has been lifted there has been no increase in the birth rate. 

In theory an excessive population could cause famine simply by exceeding the carrying capacity of the land.  Malthus built his career on the concept.  But it is a phenomenon more frequently sought than found. 

I’ve already said everything on my mind about the relationship between inbreeding depression and outbreeding depression and the occurrence of famines. 

So what is the relationship between famine and conflict?  There is the possibility of conflict over resources.  This is much spoken of, but I don’t see it much.  Possibly famine might produce conflict more than I credit.  Can conflict produce famine?  Oh, yes.  It might be incidental as Caesar described the migrating Helvetians destroying fields as they passed, and it might be a deliberate hostile move as the blockade of Germany during WW I is said to have caused millions of Germans to starve.  So the two bad things can feed make each other worse.

If cooperation can cause famine, I am not aware how.  Famine can produce cooperation to the degree that those with food send it to those without.  That is as it should be.  Of course if our high tech civilization goes down the siphon and famine goes global, foreign aid will probably not be forthcoming.  That is a day nobody wants to see.

The relationship between wealth and famine seems pretty straightforward.  If you are rich you can probably buy food.  If you are starving you are probably not very productive.  Wealth and famine reduce each other.

The relationship between famine and disease is not mysterious.  Farmers weakened by disease will produce less food.  People weakened by famine will be prone to disease. 

Finally we consider natural disasters.  Most of them occur without any human cause, earthquakes and tidal waves for instance.  They reduce the census population size, but probably have little effect on inbreeding depression or outbreeding depression; the social pressure far outlast them.  They probably don’t produce a lot of conflict as they come and go so fast, although they may have an effect on the outcome of a conflict.  The Spanish Armada was destroyed largely by their failure to get the right cannonballs onto the same ships as the guns they fit, but there was also a storm that made the defeat a lot more thorough.  Cooperation in the aftermath of a disaster is spotty.  Sometimes outsiders help a lot.  Sometimes that help seems inadequate. 

Wealth can ameliorate the effects of a disaster.  Sometimes we wonder if things like floods might be caused by the search for wealth – stripping away woodlands and wetlands that could have prevented them for instance.  Disease can follow a disaster as recent experience with Haiti shows. (The cholera they never had before may have been brought in by aid workers, but those workers would not have come in good times.)  And if a disaster reduces mobility and food supply, there you have a famine.  I don’t know of any famine that ever caused a natural disaster.

The big exception, of course, is climate change, which appears to be a disaster caused by greed, so there is a relationship between wealth that is an exception to what I said before.

So there are a number of things that impact the world.  When I say, “It’s all demographic,” it’s a bit of an oversimplification.  But so far as what we can understand but don’t and what we might be able to do something about and don’t, I’ll stand my ground and say it’s still predominantly demographic.

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