Natural selection

Char: "I don't get "natural selection"? Is that basically the same as "survival of the fitest" in a group?"

gallo: Alfred Russel Wallace and Charles Darwin co-presented papers on natural selection (Darwin's term) to the Linnean Society in 1858. Darwin then published "On the Origin of Species by Means of Natural Selection" in 1859. Darwin always gave Wallace co-credit for the discovery of natural selection, but there is no doubt that Darwin's version was much more developed than Wallace's. In fact, Darwin had discussed the idea with Sir Joseph Hooker in about 1844, so he had been working on the idea for a long time. Later, the social philosopher, Herbert Spencer, who had previously published books on evolution (Lamarckian) and economics accepted Darwin's theory in biology. He applied some of the principles to his economic and social theories, which became known as social Darwinism. It was Spencer who coined the phrase, "survival of the fittest." Darwin never liked the term because he felt it did not represent, and in fact distorted, natural selection. Nevertheless, after the term had gained popular use, Darwin was convinced by Wallace to use the term. He included it in the 4th edition of "Origin", in the early 1870s I think. But Darwin never, never used the term "survival of the fittest" without following it with a reference to natural selection.

One reason that Darwin didn't like "survival of the fittest" is that it is a tautology. Who survives? The fit. Who are the fit? The ones that survive. That's meaningless. There is also the danger that it will be used as some sort of an active principle rather than an explanation for what is observed. Survival of the fittest is not an exhortation to destroy what we consider as unfit.

Here is a summary of natural selection as Darwin presented it. Darwin observed that all organisms produce so many offspring that population size would increase exponentially if not constrained. He also observed that adult populations tend to remain relatively constant. There is also, in any environment, a limited number of resources. As a result, all organisms must be engaged in a constant competition to acquire these limited resources for themselves in order to survive. Darwin also observed that in any population there is great variability, such that no two individuals are exactly the same. Some of these variable characteristics make organisms better able (or less able) to acquire the resources necessary for life. Darwin noted that some of this variability was heritable, although he didn't understand the mechanism. Those organisms that are better able to acquire the necessary resources are more likely to reach maturity and to pass along heritable characteristics to their offspring, while those organisms that are at a disadvantage will tend to reproduce less (differential reproductive success). As a result, populations will change over time.

Note that these are tendencies in populations. Evolution has since been defined as a change in the heritable characteristics of a population of organisms over generations. We have since learned much of the mechanisms that pass along that heredity. That study is known as genetics.

Darwin's ideas about heredity were wrong and have been rejected. They were replaced Mendel's ideas of genetics. The joining of Darwinian evolution with Mendelian genetics is known as the synthetic theory of evolution (or neo-Darwinism). That was done in the 1930s and 1940s. Since them we have learned about molecular biology, population genetics, biogeography, ecology, and on and on. All of that supports the theories of evolution and natural selection as stated by Darwin.

Char: "I went to Wiki (love that site) to see if I could understand it.... and pulled this quote.

"Scientists today understand that not all evolutionary change must be driven by natural selection and that natural selection is not sufficient for evolutionary change to take place since not every trait that enhances reproduction needs to be heritable. In general, however, adaptive evolution requires natural selection because the possibility that favorable traits become more frequent across generations due to random fluctuations in trait occurrence, is negligible (see genetic drift). Favorable traits that owe their occurrence in a population to the fact that the genes encoding them became more frequent in the population over the generations through evolution by natural selection are called adaptations."

gallo: Don't get too hung up on the involvement of acquired traits in evolution. While an acquired trait might influence reproductive success, it does not drive evolution. Evolution is always a change in the heritable makeup of a population. It is never an acquired trait, and never a single individual.

There have been observed several mechanisms of evolution. Some tend to increase genetic diversity and some tend to reduce it. Natural selection, sexual selection, and genetic drift decrease genetic diversity, while gene flow, recombination, and mutation increase it. Your quote is badly stated. However, no biologist would ever claim that natural selection alone is sufficient for evolution.