Understanding Evolution

“If we evolved from apes, then why are there still apes?”

Creationists and laymen often levy this popular rhetorical question as an argument against the theory of evolution.  They reason that the continued existence of apes alongside human beings undermines the fact of natural selection.  Wouldn’t the survival of the fittest root out one or the other?  The problem with the question is that it is based on the common misconception that evolution is a linear progression.  Species do not just change into the next in orderly succession.  Evolution is a long and messy process with many opportunities for survival, death, and niche specialization.  In the case of modern apes and Homo sapiens, we are equally the successful offspring of a common apelike ancestor.

Evolution’s detractors are not the only people responsible for spreading misinformation. Some popularizers of science have inadvertently contributed to the confusion by using species comparison charts that suggest straightforward sequences of evolution.  The most famous image, the ascent of man, has become a favorite reference for comic artists and satirists.

It’s a terrific image, enlightening in its own way, but it is not the way evolution works.  Natural selection does not create a clean, linear progression from simple to complex like the image suggests, but rather it travels a bumpy road with many branching paths full of false starts and dead ends.  It was the father of evolution, Charles Darwin, who first identified the most fitting metaphor for speciation as the tree of life:

I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during former years may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have at all times overmastered other species in the great battle for life. [On the Origin of Species]

In other words, imagine you are standing over a tree and looking down so that the foliage forms a nice green circle.  Those leaves and buds along the outer edge represent the species that have survived the test of natural selection.  As you trace the branches backward in time, you will notice dead buds, extinct lines, and the convergence of surviving branches into one common ancestor, the trunk.  One of Darwin’s earliest evolutionary sketches is this very tree of life, which he jotted down in a notebook in 1837, only a year after he returned from his voyage aboard the HMS Beagle.  Thanks to modern advances in paleontology, geology, and especially genetics, biologists have constructed the most comprehensive tree of life in history.

Amazingly, the mark of our individual ancestry is etched in each unique strand of DNA and extends unbroken like a delicate branch all the way back to a single form.  It took the brute force of speciation by natural selection, a process of violent struggle, variation, death, and blind luck, to accumulate the small differences over long expanses of time that make up the diversity we see in the biosphere.  So the next time you are confronted with the question, “If we evolved from apes, then why are there still apes?” remember that every animal living today is an evolutionary success story.  After all, 99.9 percent of species that ever lived have gone extinct and, so far, we’ve all beaten the odds together.  Isn’t that a pleasant thought?

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