by Tami Port MS

Created on: June 04, 2009   Last Updated: August 22, 2009

Those who still dispute the existence of biological evolution sometimes use the argument that it is "just a theory", implying that even scientists don't agree that evolution occurs. Those employing this argument do not have a clear understanding both of how scientific investigation and evolution work. The term evolution merely means change, and biological change is observable not only in the geologic record, but also in the world around us. The aspect of evolution that scientist still investigate and debate is not whether or not this biological change actually occurs, but rather, the specific mode of evolution, what is driving the change.

* Is Evolution "Just" a Theory? *

Non-biologists discussing the theory of evolution typically confuse two separate aspects of evolution:

1. Does evolution occur?
2. How does evolution occur (i.e. what is the mechanism)?

~ Does Evolution Occur?: The first is a question of whether modern organisms evolved from ancestral organisms and are continuing to change over time. Opponents of evolutionary theory often state that scientists don't agree that evolution even occurs. Biologists consider the existence of evolution to be a fact. It can be demonstrated today, and the historical evidence for its occurrence in the past is overwhelming, and is informed by the geologic record, fossils and nucleic acid (DNA and RNA) genetic sequencing.

~ How Does Evolution Occur?: Beyond the fact that organisms do change over time, there is the important question of how this change happens; the specific mechanism. Although natural selection is considered to be the primary driver of biological change, scientists are still hammering out the specifics. Disagreement and exploration of possibilities is what science is all about; a cycle of debate and discovery. Saying that a scientific theory is invalid, due to the fact that all scientist don't agree, is nonsense.

* Evolution as Fact & Theory *

The late Stephen J. Gould, one of the great thinkers in evolution theory, explained the confusion as such: "Facts and theories are different things. Facts are the world's data. Theories explain and interpret facts". Darwin continually emphasized the difference between his two great, and separate, accomplishments: establishing the fact of evolution, and proposing a theory-natural selection-to explain how evolution occurs.

* How Does Evolution Work? *

Evolution can be defined as inheritable change in a population that ultimately results from the interaction of

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