Natural Selection and Evolution

Natural Selection Reduces the Number of Tries

Earlier a tree was used to represent the passage of time. As the tree grows, the scientist is able to climb it, and this allows him to climb steps in knowledge. The effect of natural selection on the tree’s growth is shown below. The tree is now much shorter; as a result, the steps that can be overcome by chance given several billion years are much smaller.

Figure 15.9: Natural Selection Reduces the Number of Tries

As radical as this concept may seem to some readers, it is not really in dispute. Very few molecular biologists would disagree with this particular point. Many have already stated it very clearly.

"We have no trouble understanding how natural selection can maintain a functional single-copy gene like globin or insulin. If the gene product is defective in any serious way, the organism producing it will be immediately subjected to a selective disadvantage; it will either die prematurely or produce fewer progeny that its unmutated siblings" - Molecular Biology of the Gene, Watson et al, 1987.

"As long as a particular function of an organism is under the control of a single gene locus, natural selection does not permit perpetuation of mutations which result in affecting the functionally critical site of a peptide chain specified by that locus. Hence, allelic mutations are incapable of changing the assigned function of genes." - Evolution by Gene Duplication, Ohno.

"Gene duplication must always precede the emergence of a new gene having a new function." - The Neutral Theory of Molecular Evolution, Kimura."

Small changes are cumulative only when they optimize an existing protein. Natural selection guides this optimization. Once optimized, the changes don’t stop, but they are no longer cumulative because natural selection’s role switches from one of optimization to one of preservation. Thus, large changes are not expected even if evolution is given millions of years to operate. One of the best examples of the preserving power of natural selection is insulin. Insulin in fish is almost identical to insulin in humans.

         To summarize, natural selection prevents evolution from happening like Darwin envisioned. Darwin’s small changes only optimize information.

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