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April 15, 2005

Fractals of Evolution

For a story of change, nothing beats evolution.  Richard Dawkins tells his versions of the story very well in The Ancestor’s Tale.  The form of the book is very loosely based on Canterbury Tales; it is an imagined pilgrimage backwards in evolutionary time.  On this journey, we meet various concestors (common ancestors) whose “tales” are taking off points for updates on evolutionary theory  and Dawkins’ speculations.  The book is a engrossing intellectual smorgasbord with just a few inedible plates.

We humans evolved discontinuous thinking; we like clear dichotomies: left or right, wrong or right, male or female, alive or dead, human or non-human etc. etc.   This is a useful adaptation in a world where we have to make binary decisions like fight or flight, invest or divest, and startup or don’t.  But, as Dawkins demonstrates over and over in this book,  discontinuous thinking is scientifically inappropriate.

Let’s talk about the concept of species.  We all know that the boundaries around species are defined by the inability to interbreed across those boundaries.  Not so fast; a simple thought experiment that Dawkins performs reveals that this definition contains a paradox:  “By the interbreeding criterion every individual is a member of the same species as its parents… In the Devonian Period our direct ancestors were fish.  Yet, although we couldn’t interbreed with them, we are linked by an unbroken chain of ancestral generations, every one of which could have interbred with their immediate predecessors and immediate successors in the chain.”

He is not saying that there aren’t different species, just that they exist as segments in a continuum with no clear demarcations at the boundaries.  A contemporary challenge to discontinuous thinking about speciation is the existence of ring species.  In Camp Wolahi at the south end of California’s Central Valley there are two distinct species of salamander which do not interbreed.  Salamanders don’t live on the valley floor.  One species dominates the east rim of the valley and the other the west and they meet but don’t mingle here in the south.  At the north end, however, there is only one species of salamander whose physical traits are a mix of the two species at the other end of the valley. In fact, as you go north along either rim of the valley, each of the species which is so distinct at the south end begins to look more like the other until, at the north end, there is just one homogenous population.

Similar continuities arise when we try to distinguish between multicell individuals and colonies.  Coral and jellyfish make interesting examples at the non-discontinuous boundary line.  Ant and termite hives can be tough to categorize.  Even our own bodies pose some paradox despite our strong belief that we are individuals.  What about the mitochondria which apparently sneaked into our cells from outside at some point in the evolutionary process and follow their own chain of descent from mother’s egg to mother’s egg and have their own DNA?  Are they us or are they hitchhikers?

This is mental calisthenics at its best.  There is no answer to these paradoxes.  Dawkins’ genius, once he limbers our minds, is to point out that the paradoxes arise from discontinuous thinking and can’t be resolved in that context.  In a world which is supposed to be only black and white, there is no explanation for gray. I won’t draw the obvious parallel to many of our political arguments, at least in this post.

Because I am a change addict, I was delighted to read Dawkins speculation that evolvability itself may be undergoing evolution.   It is reasonable to think that there is survival value to being able to change in either a stable or a changing environment.  In fact, evolving species create a changing environment for each other even if the air, water, and earth weren’t changing.  The ability to change also increases the ability to colonize new environments.  Some of the watershed events in the evolution of evolution could be the formation of DNA molecules (earliest life may have been RNA-based), the development of the cell membrane, multicellular organisms, and the segmented (modular, to nerds like me) body plan.  Stretching a little further, selective breeding by humans is another step in the acceleration of evolution.  Now we have genetic engineering which is a consequence of a mind which evolved to be able to invent forced-pace evolution.

The indigestible parts of this smorgasbord are mainly a result of political correctness.  There are a few, apparently mandatory, cracks at President Bush.  I don’t care about Dawkins’ political views and they seem intrusive and small in such a large canvas as the history of evolution.  More serious is his vitriolic feuding with and gratuitous insults to creationists.  It is unscientific to treat Darwin’s theory of evolution as if it were a religion and all who question it as heretics. The evidence is overwhelming (to me) that Darwin was correct at the fifty-thousand foot level.  So was Newton.  So was Einstein.  Theories evolve, too; and they evolve when they are questioned, not when they are unconditionally accepted.  I think progress in understanding evolution may be retarded by a politically correct suppression of questions.  Stephen J. Gould’s theory of punctuated equilibrium, for example, is not given the respect I think it deserves because Gould posited it as an answer to creationists’ questions about gaps in the fossil record.  In respect to the feud between creationists and Darwinist, Dawkins is guilty of discontinuous thinking.

In previous posts, I blogged my own unqualified theories about why humans are born helpless and the fate of complex ecosystems.

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