Evolution and Fitness

One of the basic pillars of the theory of evolution is the fact that every species gives birth to far more offspring than the planet can sustain. This fact sets up a perpetual competition for survival among species. Those creatures who are the most fit survive in a given situation and pass their genes into the future. Those less fit die out, or never get a chance to procreate. It's that simple.

A key part of this scenario is the fact that tiny mutations randomly occur, each time a newborn comes into the world. The DNA of every species is duplicated at birth with an amazingly high degree of accuracy, but because there are millions upon millions of DNA copies to be made, tiny copying errors will inevitably creep in.

Those errors are precisely the source of tiny variations between otherwise identical offspring. Thus, one baby within a family will slightly be different from another. One sparrow born in Georgia will be a wee bit genetically different from one born in Florida, or even within the same locale in Georgia.

These slight differences rarely have any import, but should the environment—or other external conditions shift ever so slightly, one critter may fare better than another. The Georgia sparrow, for example, may have a slightly more yellow color. That yellower sparrow may be less visible to new predators—who, say, have migrated there due to climate change—who don't see yellow as well. Thus the yellow birds will live to have babies, who will also have the yellower gene. The result: yellower sparrows win the competition for survival.

This is basically how life has evolved on Earth. Every time environmental conditions have shifted, some critters—just by luck—are more fit in the new environment, and they successfully send their modified genes into the future. This amazing process is what has allowed life on our planet to adapt to changing conditions, and then to evolve new life forms to thrive in new conditions. This process would not happen without an overabundance of babies born to each species (otherwise every baby would prosper and never face the prospect of an early death). There would be no competition between their minuscule differences, to see which one wins.

One way to appreciate this magnificent process is to ponder what might happen if life on Earth had settled into some kind of happy stasis, where no competition occurred. What if the number of babies born was exactly what was needed to sustain each species? Wouldn't that be much more peaceful? If that were the case, there would be far less competition, no survival of the fittest, no dog-eat-dog world. Every critter would find its happy place; the lion could even lie down with the lamb.

But what would such a world be like? For one, evolution would simply not occur. Every critter would be content, would be secure, and would be very comfortable. No changes. Everything would become static and unvarying. This might sound nice, but what would happen if a small perturbation in the environment happened to occur? All those placid critters would suddenly be faced with challenges for which they are totally unprepared. There would be massive extinctions. Life, that would long have ago settled into a kind of inactivity, would now be unable to respond. Most creatures would go instinct!

So we might well celebrate what appears to be a brutish form of competition in nature, where too many babies are born and most of them die or get eaten. It may appear to be cold-hearted and devoid of any gentleness, but it has kept life vital, robust, and progressive, for several billion years. Let us be thankful for nature's wisdom.