Mark Twain once provided this perspective on statistics.  "In the space of one hundred and seventy-six years the Mississippi has shortened itself two hundred and forty-two miles. Therefore ... in the Old Silurian Period the Mississippi River was upward of one million three hundred thousand miles long ... seven hundred and forty-two years from now the Mississippi will be only a mile and three-quarters long.  There is something fascinating about science.  One gets such wholesome returns of conjecture out of such a trifling investment of fact."  

Speaking of facts, the population of the U.S. is poised to hit 300 million this month.  For those of you who regularly drive in Chicago, Boston, L.A., or any other major metropolitan area, this statistic will warrant little more than a shrug.

But if you live in one of the "fly-over" states, you might raise an eyebrow at such a figure.  Speaking of flying over, when you do fly over America, it's hard not to notice that most of it is undeveloped.  In fact, nearly 95% is undeveloped!  And much of that other 5% is poorly developed (e.g. Gary, Indiana). 

Nevertheless, 300 million is a lot of people, and it often seems like more than half of them are ahead of me in line at the grocery store, possibly unaware that they are breaking the items count rule since they don't read English.

Yes, the primary factor in America's population growth is immigration.  The U.S. admits more legal immigrants every year than all other countries combined.  Were this not the case, we might be suffering from some of the difficult population shrinkage issues currently plaguing Europe.  It's hard to support a bunch of retirees if there are not new workers replacing them on the tax roles.  But immigration is tradition here.  This has been true for much of our history, and is a key ingredient in the "American Dream".

The number 300 million is not technically any more important than 299,768,423.  But it's easier to say, and it certainly carries more symbolic weight.  We like our nice round numbers.  They give us an opportunity to pause, look at where we've been, and consider where we're headed.  America hit 200 million back in November of 1967.  I did my part, getting myself born in July of that year.

This (the 200 million mark, not my personal birth) made biologist Paul Ehrlich so happy that he wrote "The Population Bomb", in which he predicted worldwide famine and mass starvation by 1975.  The planet's inability to produce enough food to feed the growing population made a near term future of rationing and war a statistical certainty.  

As we hit 300 million, the majority of Americans from every socioeconomic background struggle with being overweight.  And it's not just Americans who are fat.  Human ingenuity has allowed for the production of far more food than people can hope to consume, though we still manage to starve some for political purposes.  Ehrlich didn't see that coming, and famously lost a bet with economist Julian Simon, who rightly predicted that innovation would outpace need.  Ehrlich chose five metals whose value he was sure would increase due to their diminished availability over time, with Simon agreeing to pay the difference in market price after ten years.  It seemed like a sure bet - after all, the available quantity of each metal would do nothing but shrink, and the more rare something is, the more expensive it is, right?  Wrong, held Simon.  Once a material becomes too rare to use, it gets replaced, and its value drops.

In any event, we no longer worry about overpopulation.  Under-population is more of a problem for much of the developed world.  Instead, we worry about global warming.  Al Gore is traveling the world explaining his Inconvenient Truth, which I at first thought had to do with losing the election upon which his life had been predicated, or finding out he hadn't invented the internet.  Instead, it deals with the overwhelming evidence that the planet is heating up, and the statistical certainty of worldwide devastation we now face as a result.  Sound familiar?

Interestingly, in the 1970s, the inevitable disaster was a new ice age, brought on by the global cooling trend that science was incontrovertibly demonstrating (according to some, the same "some" who now trade in global warming catastrophe predictions).

Does this mean that science is always wrong?  I doubt it.  Should we ignore the preponderance of evidence upon which the majority of scientists seem to agree?  Doesn't seem wise.  But we might want to put a little more faith in human ingenuity, which after all has a strong track record (both for good and ill).  And perhaps we should adopt a bit less of a Chicken-Little approach to statistical predictions.  Certainly we should responsibly measure the real impacts of the policy decisions we make, as individuals, communities, and countries.  That includes not only attempting to predict long term affects on the environment, but also short term affects on things like productivity, employment, inflation, etc.  In other words, closing a polluting factory that employs half the people in a community in order to stop it from contributing to long term global warming might be a bad idea.  On the other hand, requiring politicians to keep their mouths shut for a while so that their hot air won't contribute to global warming has no perceptible downside.

The responsible person makes reasonable sacrifices today so that he is prepared for tomorrow. But surely it is foolish to sacrifice all or most of today, which after all is here, for a tomorrow that may not come, or will be far different from what we imagined.

*NOTE: Several of the stats I noted in this column come from an excellent article by Joel Garreau appearing in this month's Smithsonian magazine.