Life on Planet Earth

As a mental exercise, try to characterize the phenomenon of life as it exists on this planet. Some applicable ideas: Diversity, variation, change, complexity, interrelationships, vigor. How can one account for all of this? Where did it come from? Where might it be going?

Not surprisingly, there have been many who have attempted to answer these questions. But before we consider the history of such ideas, a few definitions will be useful.

A species is a group of organisms that actually or potentially interbreed and are reproductively isolated from all other such groups.

Evolution (that highly-charged word) refers to change over time, with the presumption of "progress" or increase in complexity and diversity and the acquisition of distinguishing characteristics. I find that "progress" is quite often in the eye of the beholder, subject to the observer's own worldview. Similarly in contemporary Western culture "progess" is frequently a codeword for "that which I prefer to see happen," or quite simply "the good."

The theory of evolution--whatever that means--has been described by one science educator as "the greatest unifying theory of biology" that allows us to understand differences and similarities between organisms, that explains the appearance of purpose (no teleology here, please--we're Scientists), and that emphasizes the dynamic relationship between structure and function. That the theory bears such a weight on its shoulders goes a long way to explaining why it is so vigorously defended by its adherents and why alternative explanations for origins are often dismissed, derided, or fought with passion.