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From Charles Darwin's 1859 book "On the Origin of Species "
In spite of (or perhaps because of) the prolific amount of posts PZ Myer’s pens for his blog Pharyngula over at Scienceblogs, I have trouble being a frequent reader. He focuses on a wide variety of topics, many of them uninteresting to me, but one that I find him to be a terrific source of entertainment: evolution. In an uncharacteristically long post over the weekend, PZ delved into an easily digestible essay on just a few of the more complex and frequently misunderstood aspects of evolutionary theory. Given the attention that TQM paid yesterday to a journalist’s misunderstanding of Intelligent Design, I thought it was worth continuing the conversation.
PZ is correct that evolutionary theory is now a rich field of study that is commonly distilled down to an inadequate sound-bite for mass consumption. I encourage you to read his post. But I wanted to add my own commentary on one level of complexity that I find lay-people often gloss over when summarizing natural selection as a mechanism for evolution.
EVOLUTION IS CONSTRAINED BY HISTORY. The misunderstanding is that natural selection will produce whatever is necessary for whatever environmental pressures that present themselves; this is an oversimplification. Natural selection has to have something to work with. PZ spent most of his article talking about natural variation with serves as the scissors, tape and paper that evolution alters. We can think about this variation on a larger scale. For instance, let’s say that a population of some four-legged animal were to develop a octopus-like tentacle that was extremely adaptive to their environment, chances are MUCH greater that the tentacle would evolve from an existing appendage, maybe the tail or an arm or a nose, rather than develop anew from the body of the animal. This is because natural selection works with what it has got. This can go the other way too. Sometimes an organism is stuck with something, a loosey-goosey octopus-like tentacle instead of a sturdy tail, because it is leftover from an ancestral species that experienced different selective pressures. This is one of the key points that Gould received both praise and criticism for railing against. Structures or behaviors do not necessarily need to be adaptive to be products of natural selection. Bi-products and left-overs do seem to be rampant in animal and plant biology and indeed are a major source of variation.
PZ’s post had substance and clarity. And a reminder that evolutionary theory is not simple, not to those who espouse its merits or to those who disregard the mountain of evidence supporting and defining it.
Resources for learning more:
University of California Museum of Paleontology and Berkley have an informative site
Richard Lenski writes at Action BioScience
My fav, the NYTimes series “On Darwin’s Origin of Species”
