My Take on Natural Selection


It is mind-boggling to think that every living thing on this planet evolved from a single common ancestor which probably resembled the stuff that grows in the back of your refrigerator. And yet, we are told, this is really how it happened. Not only did complex organisms such as platypuses and mulberry trees develop from the same simple origins, but it all happened by accident. How can we explain this overwhelming concept without resorting to supernatural or divine forces?

At the core of every organism are the genes. These control how the organism will develop, when it will develop certain traits or behaviors, what kind of a body it will grow, and most other physical and behavioral parameters. In a given population, sometimes several variations of a gene will exist which have control over the same parameter, but with different values. For instance, the gene(s) for whether a cat has a tail or not control the same parameter (tail-having-ness) but with different values: yes or no. Genes which yield different values for the same parameter are called alleles.

On any given chromosome, only one of a group of alleles can take up residence. For instance, if the aforementioned cats' gene pool only came with two alleles for tail having-ness, then some cats would have the chromosomes with the "yes" allele on them, and some cats would have chromosomes with the "no" allele on them. These chromosomes would cause the cats to develop (or to not develop) tails accordingly. If an allele (let's call it A) causes its organism to be replicated more than a fellow allele (named B) causes its to be replicated, then allele A will eventually be on all the chromosomes and allele B will die off. For illustration, let us suppose that having tails causes cats to live longer than not having tails; a tailed cat has better balance, so it won't fall out of trees as often as a tailless cat. Let us further suppose that over a tailed cat's lifetime, she will produce 50 kittens who live to maturity. The tailless cats, however, tend to die earlier due to falling out of trees and breaking their backs. In her shorter life span, a tailless cat will only produce 30 kittens who live to maturity. In other words, after only one litter, the tail-having allele has gotten itself copied 50 times, while the non-tail-having allele has only gotten itself copied 30 times. The number of tailed cats will continue to grow faster than the number of tailless cats until the tailless cats dwindle off into oblivion. In this way, certain alleles are 'selected' not by a volitional being, but by nature.

We still have not solved the question of how such diversity as we see around us every day could have evolved from the same ancestor. For one thing, if there was one ancestor, where did any alleles come from? Wouldn't all the little pond scums have the same genetic code as the original pond scum? For the creation of the alleles, we have genetic mutation to thank. Sometimes, when an organism is copying its genes to pass on to its offspring or clones (depending on what kind of sex life our organism leads), a little tiny piece of the code gets copied the wrong way. The result is a chromosome slightly different from the original. In many cases, the difference is inconsequential but eventually a mutation will occur which benefits the lucky organism or its offspring somehow. It may allow for better food digesting, letting it spend more time reproducing and less time eating. It may increase the life span, allowing it to reproduce more times in its life. In a population of identical pond scums, this advantaged individual's special allele will quickly outstrip its blander fellow allele.

The question arises, why don't all the pond scum eventually end up with this new allele, and be identical again? The new allele is obviously better than the old one, so there's no reason for the old one to remain in the population's gene pool. This brings us to the last building block in our theory: the influence of the environment. All of the pond scum might not be floating around in exactly the same living conditions. The south end of the pool might be warmer than the north. The middle may be deeper than the edges. At some point, a mutation will occur that will only benefit part of the population because of the varied environment. In this way, different alleles spread throughout the population. Eventually the organisms will change so much that they are no longer the same creature.

Natural selection is what we call this mechanism whereby organisms change and develop through time. Because of different environmental factors, certain alleles are selected over other ones in different parts of a population. Soon different organisms arise. These are continually selected and changed by their environment over time until there are as many organisms as there are ecological niches, much the conditions we see today.


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Last modified: November, 1996