In one of my classes today, my professor did a quick aside review on the Malthusian theory of population, which was an 18th century postulation that the human population would grow exponentially until it outstripped the planet's resources and agricultural production - way too many people squeezing into limited space, fighting each other off for limited food, hacking each other up and going cannibal etc. I made that last one up. It could probably happen, though.
BUT not to worry, it has since been pretty much determined that Malthus' gloomy prediction won't come true. Why? Because the population rate will not increase exponentially for ever and ever. After the initial period of exponential increase, mediating factors kick in to slow the growth rate. The earth likes balance. Humans take from the earth, but we also give back, and biology wants to maintain this homeostasis. So eventually, the population levels off. There might be periods of flux one way or the other, but the population won't spiral up out of control. From my understand, this general pattern doesn't just apply to the human population, but also to things like animals, bacteria, fungi, etc. (This is a reeeeally rough explanation. I'm not a scientist. My facts are coming from five minutes of a class lecture, my vague memory of high school biology, and some poking around on Wikipedia. Scientifically-inclined people, definitely chime in and correct me if I've got it totally wrong.)
Anyway, does this remind anyone else of set point theory? Maybe it's just because weight gain is on my mind all the time lately, but instead of seeing my professor standing up there with his little laser pointer, I was seeing my dietician J in her office trying to convince me that a 0.8 lb blip on the scale does not signify impending obesity. (I'll gladly accept second opinions on that one though!) On an appropriate meal plan, the body of an underweight anorexic will gain weight until enough weight has been gained, and then it will stop. I haven't done enough research on the set point idea to know exactly where I stand on that one (if I'm not mistaken, it's still somewhat controversial, no?), but I definitely believe that the body has a healthy range within which it wants to stay, and within which it will stay if fed a healthy, reasonable number of calories.
Bodies, populations - nothing can grow exponentially forever. It just can't. I know this. But for some reason, it's much easier for me to believe that microbial bacteria in the ocean will obey the laws of biology and physics than for me to believe that my body will behave in an equally appropriate fashion. Logic: reveal yourself!