The Theory of Evolution



The basic tenets of the theory of evolution are ...

  • Nature's imperfect reproductive methods regularly produce mutations, so that there are always unique individuals.
  • Individuals that, as a result of those mutations, are better adapted to their environment will have more offspring, either because they survive more often or are better able to attract mates.
  • Those more suitable adaptations will be prone to spreading through an entire population.
  • Over time, as those adaptations accumulate, populations are modified into new species.
  • Given the immense amount of geologic time on this earth, this process, known as natural selection, has produced all life on the earth from one or a few parents.

Those are my words. On this page, I'll give you science's definition of evolution, and then we'll look at a couple details that are important to the creation vs. evolution debate.

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Definition of Evolution

The most basic definition of evolution is change over time. To be more specific:

Evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next. (Helena Curtis & N. Sue Barnes, Biology, 5th ed. [Worth Publishers, 1989] p. 974)

Has the Theory of Evolution Evolved?

The theory of evolution has progressed since first presented by Charles Darwin in 1859. There have been many important discoveries over the last 150 years.

Alleles are genes that vary from individual to individual. For example, among humans I might (and apparently do) have a gene for brown eyes while my wife has a gene for green eyes. The two genes both code for the same trait—eye color—but produce different results.

So the most basic definition of evolution is not controversial. Evolution is the change in the frequency of alleles in a population. So if Americans became 90% blue-eyed, then evolution would have occurred.

The Evolution of the Eye

It seems hard to believe that something as complex as an eye could be produced by "a change in the frequency of alleles," but the explanation for how that happened is very convincing.

No one has a problem with that. The question is, do changes in frequency of alleles in a population accumulate over hundreds of millions of years to the point that humans can descend from bacteria?

Ah, now that's a question.

The answer, unfortunately, has to be relegated to other pages. We're not going to answer that on one page.

Further Definitions of the Theory of Evolution

Here's a couple more quotes just to show that the most basic definition of evolution is change of any sort.

What constitutes a small step?

That's certainly a question I had when I was researching whether the theory of evolution is true.

In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve. (Douglas Futuyma, Evolutionary Biology [Sinauer Associates,1986])

Biological evolution, simply put, is descent with modification.This definition encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). ("An Introduction to Evolution"; from the University of California at Berkeley web site)

Again, no one disagrees that evolution happens. The question is, has evolution been going on, bit by bit and small step by small step, from bacteria to modern life?

Abiogenesis: The Origin of Life

Note that the theory of evolution begins with the first cell. The science that studies how a first cell might have arisen from non-living molecules is called abiogenesis.

Does the Theory of Evolution Rely on Chance?

Arguments against the theory of evolution regularly point to the remote possibilities of certain structures arising by chance. Evolution does not rely on chance.

Another term for the theory of evolution is natural selection. Selection is the opposite of chance. Selection is choice. The theory of evolution teaches that nature selects certain individuals by the struggle to survive in much the same way a farmer selects cows that produce the most milk.

The theory of evolution involves two steps:

  • Mutations: these are errors in the genetic code that occur by chance because reproduction in nature is never perfect.
  • Natural selection: this is the process by which nature weeds out mutations that negatively affect survival and preserves those that help survival (or reproduction).

The first of those steps really is chance. Mutations occur in every generation, and so they provide abundant raw material upon which selection can work.

The second of those steps is not chance at all. Mutations that increase the possibility of reproduction are preserved. Such mutations will accumulate over successive generations leading to large changes over time.

That is the theory of evolution.

It is the rest of this site that is devoted to determining whether it is true.

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