Thoughts on Evolution : Definition

Our discussion group has occasionally focused on the topic of Evolution, attempting to understand its true nature and recognize both its creative power and limitations. The following summarizes my opinions on both the general topic of evolution, and various specific points we have covered.

The definition of Evolution has itself been a matter of small controversy. Dictionary definitions are somewhat inconsistent. Here are the biological definitions from a few sources:

“The theory that groups of organisms change with passage of time, mainly as a result of natural selection, so that descendants differ morphologically and physiologically from their ancestors” (American Heritage)

“a process of change in a certain direction”, “a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations ” (Meriam-Webster Medical Dictionary)

“a process of continuous change from a lower, simpler, or worse to a higher, more complex, or better state ” (Meriam Webster)

“a process in which something passes by degrees to a different stage (especially a more advanced or mature stage)” (WordNet)

My personal understanding of the concept of (biological) evolution is a process of gradual change through distinct generations of individuals of a defined species in which the average fitness of the individuals improves relative to the species’ environment.

A question which we have repeatedly faced is whether a progression from “simple” to “complex” organisms is an intrinsic aspect of evolution. Notably, the definitions given above vary between including or ignoring this further refinement of the term evolution.

Harry Bingswanger, in a lecture given expounding his thesis “The Biological Basis of Teleological Concepts”, defined evolution as a progression from simplicity to complexity, and marked evolution as the process by which goal-directed actions (perhaps more descriptively termed “behaviors”) are created in species (as well as physical, structural properties of species). I (respectfully) disagree with including the progression from “simple” to “complex” as an essential element of the concept of evolution.

First, let me provide a thought experiment as a counter-example. Let’s assume that Mars once had an environment conducive to the development of complex living organisms – liquid water was present, the atmosphere was denser, and temperatures above freezing were common – and that complex life forms were abundant. Then, as the planet “aged”, the environment gradually changed toward today’s condition (arid, little or no water and oxygen, continual sub-freezing temperatures). Under these increasingly hostile conditions, it is rather easy to conceive that simpler life forms had a fitness advantage over more complex forms, and that evolution resulted in a reduction in complexity, perhaps ending in microbes [which I can conjecture may yet exist on that planet] as being the dominant life form. A fair response to this “counter-example” is that it is non-existent (to our knowledge), and that the one and only example of the actions of evolution on a global living system exhibits a progression from simple to complex organisms.

My concept of evolution, however, is based upon more than biological evolution. With some considerable experience in the use of evolutionary algorithms to perform optimizations, I have abstracted my concept of evolution to encompass both the mathematical formulations of evolution, as used in optimizations and various simulations of “artificial life”, as well as biological evolution. The variations upon the mathematical formulations of evolution are extremely numerous, while the underlying processes of biological evolution at the DNA level may be as numerous. The definition I suggested earlier for evolution fits my understanding of both the biological and mathematical forms of the process (to my current knowledge, of course).

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