Natural Selection

Evolution by Natural SelectionCharles Darwin recognized that selection is the most important mechanism acting upon variability to bring about long-term, intergenerational change. Individual organisms that are better adapted to an environment are more likely to survive and reproduce.

Darwin accurately predicted that his theories would evoke skepticism from scientists and ridicule from the religious. Happily, scientists came to accept his ideas, and his breakthrough insights have proved highly influential. Unhappily, those biblical literalists who insist that Biblical Book of Genesis is an accurate description of life's origins, continue to unjustly vilify Darwin's theories.

“Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic.” Darwin, "Origin of Species", Ch. 4

Summary of Darwin's observations and his Theory of Evolution by Natural Selection:
1. Most animals have such high fertility rates that their population size would increase exponentially if all individuals were to reproduce.
2. Yet, except for seasonal fluctuations, populations remain relatively stable in size.
3. Because environmental resources are limited, individuals compete for resources, limiting survival and reproduction.
4. Individual characteristics vary within populations and those members of a population that are better adapted for survival in the face of competition are more likely to pass their characteristics on to the next generation.

Conclusion: 5. Thus, species gradually accumulate inherited adaptations that best suit them for their environment, passing these on to progeny. Speciation involves gradually accumulated differentiation of characteristics.

Subsequent evolutionary theorists first disputed Darwin's concept of gradual evolution. Gould and Eldredge introduced the concept "phyletic gradualism " which they discredited through the concept of punctuated equilibria. The Theory of Punctuated Equilibria was proposed in order to explain patchiness in the fossil record and the the localized adaptive radiation of species observed following extinction events. This stage of thinking about evolutionary mechanisms has been termed "Neo Darwinism".

The modern synthesis of evolutionary theory combines an understanding of the genetic mechanisms (genotype and regulation of expression) that determine phenotype, and population genetics explains the fate of genetic variability (alleles) within populations of organisms.

In their attempt to discredit evolutionary science, creationists and defenders of "intelligent design" creationism commonly attack a straw man depiction of Darwinism or Neo-Darwinism as representing current thinking. It is important for any person wishing to defend evolution-as-fact and modern evolutionary theories to attain a thorough understanding of modern evolutionary theory as well as fallacious creationist arguments. For example, creationists who attack evolutionary theory in the vain hope that this will "prove" the existence of a "God" are creating a false dichotomy and relying upon a fallacious argument from ignorance.


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