Slowly but Surely . . .

An objection often raised against natural selection is that mutations are too rare to drive all the change and produce all the variation we see around us. However, natural selection is an extremely powerful concept that can accumulate tiny incremental changes into vast differences over time. This is called cumulative selection. Many people mistakenly believe that natural selection consists of random attempts to change one type of organism immediately into another. This view, called single-step selection, is simply untrue and rests on the premise of saltationism (see previous section). Natural selection is the accumulation of extremely numerous micromutations over vast periods of time. For a demonstration of this principle, see our Breed Your Own Text simulation, which demonstrates the power of cumulative natural selection on user-provided text.

Alternatives to Natural Selection

Despite the prominence of natural selection in much of evolutionary research, some scientists are developing plausible theories of additional evolutionary mechanisms besides natural selection. The most reasonable of these is genetic drift, which states that another force in evolutionary change is the accumulation of small, random, irrelevant mutations not acted upon by natural selection. Although this is often termed non-evolutionary change, "evolution" is most generally defined as "accumulated change over time", so the name is not exactly applicable. A better description would be "non-adaptive change". Some such mutations in certain genes take place at a specific rate and can be used in the relative dating of biological organisms. This technique allows estimates of how long ago two organisms' ancestors diverged in the "evolutionary tree"

Another recently advanced alternative to natural selection is the application of complexity theory to biological systems. This idea relies on the assertion that matter has a tendency to self-organize into complicated systems, such as living organisms. Little evidence currently exists for this theory, and it is sometimes considered to be little more than a half-baked notion. However, it has its advocates, and it will eventually stand or fall on the evidence.

The "Guiding Force" of Evolution

Natural selection is often seen as the "guiding force" of evolution. Indeed, many people see natural selection as a way to reconcile religion and evolutionary theory by postulating that evolution is divinely inspired or that a divine being guides the selection process. Others take a less mystical view and argue that evolution by natural selection will by definition produce progressively more complex organisms, culminating in a self-aware species such as mankind. Still others take offense at the "cruelty" and "heartlessness" of a principle that favors the strong at the expense of the weak. All these arguments are attempts to mitigate the "demotion" of humans from their central place in the fundamentalist view to their purely contingent place in the strict evolutionist's universe. The philosophical and sociological implications of natural selection and its various interpretations are discussed in Evolution and Philosophy.

Looking Further: Links and References

The following links and references will be useful in the study of natural selection, differential reproduction, and survival of the fittest.

• Books
  • The Descent of Man by Charles Darwin
  • The Origin of Species by Charles Darwin
  • The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design by Richard Dawkins
  • The Selfish Gene by Richard Dawkins

• Websites
  • The World of Dawkins (unofficial)
  • Online Biology Book - The Modern View of Evolution
  • Darwin and Natural Selection

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