Sunday, July 14, 2013

Natural Selection for Efficiency

At the moment, I am able to post essays from a different location than what I normally use. My usual location remains unworkable. I now resume my usual series of essays.

In a previous essay I wrote about how our economic system is (almost) forcing us to waste resources. In nature, sexual selection often favors wastefulness (think of colorful bird feathers and flowers), and in the human species, social and sexual selection can favor conspicuous consumption. However, this always occurs within the broader picture of natural selection favoring efficiency.

One example is the evolution of CAM, which is a type of photosynthesis found in many succulent plants. The leaves of most plants absorb carbon dioxide and make it almost directly into carbohydrates such as sugar during the daytime. But CAM plants absorb carbon dioxide at night, make it into acid, store up the acid, then use the acid as a source of carbon dioxide from which to make sugar in the day. Carbon fixation therefore occurs in two phases: the night shift, and the day shift. And, like a factory that might need to hire two sets of employees rather than just one, this system is more expensive than just making sugar during the day shift. In fact, the night shift consists of an almost completely separate set of enzyme reactions from the day shift.

Under cool, moist, or shady conditions, CAM would be clearly wasteful. As my educational mentor from grad school days said, CAM plants don’t have it made in the shade. But CAM plants grow in desert conditions. In order to absorb carbon dioxide during the day, a plant has to have its pores open, and when it does so, it loses water vapor. In a cool, moist, or shady environment, this is not much of a problem. But out in the desert, it might cause the plant to lose too much water. For succulent plants it is more efficient to open their pores at night, when it is cooler, and store it up in the form of acid. The wasted energy is more than compensated by the water that is saved.

Here is an analogous situation. Suppose you have a factory that has to shut down on hot days. But even when the factory is shut, you still have to pay the workers. Is it cost-effective to pay a night shift of factory workers so that the factory can stay open in the summer? It depends. If the factory is in Minnesota, probably not. But in the desert, such a factory would be closed from May through September. Not surprisingly, CAM plants are more common in the desert than in Minnesota.

It seems obvious that CAM photosynthesis has evolved and become common in conjunction with the spread of deserts in the late Neogene period. And it has evolved more than once, as existing enzymes have been reassigned to new functions. However, it appears that CAM may have first evolved as an adaptation to low carbon dioxide availability rather than to hot, dry conditions. How else to explain CAM in primitive aquatic plants such as Iosetes? (See the article by Jon Keeley.) A similar adaptation, C4 photosynthesis, may have first evolved in grasses not because of hot conditions but because of low levels of carbon dioxide during glacial periods especially in tropical highlands. CAM and C4 photosynthesis may have begun as an adaptation to low carbon dioxide availability, and they later proved useful in hot, dry conditions. (I did not explain C4 in this brief entry because it’s more complex.)

Everywhere you look in the world, natural selection has favored efficiency. In many cases, after the needs of efficiency have been met, sexual and social selection have favored wastefulness. But in our society right now, we continue our binge of wastefulness even when we are not meeting the basic needs of efficiency.

We may have to learn not just efficiency but extreme frugality in the decades ahead of us. Of course, it is possible that the very rich, and people with lots of guns, might not have to do this, but then there’s the rest of us. Stories from the past tell us that much human creativity has been employed in the invention of new forms of frugality. I grew up hearing stories about how Native Americans used every part of the bison (in contrast to white Americans, who would shoot a buffalo, cut out the tongue to eat, and let the rest rot), and my Dad telling me that a World War II soldier could clean up, shave, and brush his teeth using one helmet-ful of water. Storing runoff water from the roof in cisterns is a practice thousands of years old. The thrifty Scots did not waste anything from sheep; hence the invention of haggis, which (in its original form) was a combination of oatmeal and sheep lung and other organ tissue and which is reportedly a food item.

We can only hope that, when called upon to do so in the years ahead, we humans can display the kind of creativity in our cultural evolution that CAM and C4 plants have displayed in their biological evolution. Sexual and cultural selection can favor wasteful displays, but only if there is a surplus of energy, materials, and opportunities, however slight, left over from the demands of natural selection. A big colorful male bird that starves is just a dead bird.

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