<p><i>Photograph by George Grall, National Geographic Stock</i></p>

Photograph by George Grall, National Geographic Stock

Evolution vs. Intelligent Design: 6 Bones of Contention

On the 150th anniversary of Charles Darwin's On the Origin of Species, we look back on 6 pieces of evidence that still spark debate today.

On November 24, 2009--the 150th anniversary of Charles Darwin's On the Origin of Species--the theory that new species can arise from old ones through natural selection is still met with some resistance.

1. The Eyes Of The Vertebrate

Why Intelligent Design?

Some of evolution's most vocal critics are proponents of "intelligent design," arguing that many structures in plants and animals bear the unmistakable signature of design by a supernatural intelligence.

Intelligent design proponents say the eyes of vertebrates--including humans and the common snapping turtle seen above--could not have evolved in a stepwise fashion. That's because the eye is made of several interacting parts, and the removal of any one part will cause the entire system to cease functioning. Thus, the argument goes, the eye must have been produced in one fell swoop.

"If you look at these [evolutionary] schemes, they often very abruptly add a lens or a cornea," said Casey Luskin, a spokesperson for the Discovery Institute, a Seattle-based organization that advocates intelligent design. But things don't just appear suddenly in evolution, Luskin said. "You need to evolve things in a step-by-step fashion."

Evolutionists Argue ...

Steps in the evolution of the vertebrate eye exist in the fossil record, said Don Prothero, a paleontologist at California's Occidental College and author of Evolution: What the Fossils Say and Why It Matters.

"There've been multiple, very well-documented papers showing how complex structures like the eye can evolve in gradual steps from a simple eye spot that is just barely a light receptor all the way to things like the human eye," Prothero said. Intelligent design advocates, he said, simply ignore the evidence.

2. The Cambrian Explosion

Why Intelligent Design?

The Cambrian explosion refers to a period in Earth's history 530 million years ago when new species of unprecedented complexity--like the predatory Anomalocaris depicted above--appeared in the fossil record within a relatively short time span. The lineages of nearly all of today's living organisms can be traced back to this flowering of life.

According to the Discovery Institute's Luskin, the Cambrian represents "abrupt explosions of mass biological diversity that required huge amounts of information be injected into the biosphere rapidly. In my view, only an intelligent agent can account for the origin of information in such a rapid fashion. I don't think a step-by-step, neo-Darwinian process is up to the task."

Evolutionists Argue ...


The Cambrian explosion was not an explosion at all. "It's a three-billion-year-old 'slow fuse,' and we have the fossil record that shows this," Occidental College's Prothero said.

In addition, "we now have fossils of all sorts of soft-bodied and microscopic things from before the Cambrian, and you can see very clearly how from simpler things you can get more complex things."

3. DNA


Why Intelligent Design?


As a blueprint for nearly all forms of life on Earth, the DNA molecule (seen above in an artist's rendering) could be said to have a high degree of complex specified information, or CSI. Using only four chemical bases as "letters," DNA encodes within its spiral structure the instructions for all the proteins an organism needs to survive.

High CSI refers to objects or phenomena that are both complex and highly specific--just like, for example, language and machines, which are products of human intelligence. "Systems that have high CSI only come from an intelligence," Luskin said.

Evolutionists Argue ...

Once the molecular ingredients for DNA came together, natural selection took over to create increasingly complex--and yes, specific--molecules suitable for use in genetic code.

While no supernatural hand guided the evolution of DNA, "natural selection [was] a non-chance component," Prothero said.


4. Bacterial "Legs"


Why Intelligent Design?


Some bacteria move around using whiplike structures called flagella, each one made up of dozens of complex, interconnected protein parts.

Intelligent design advocates say that, like the vertebrate eye, the bacterial flagellum is "irreducibly complex," because the absence of any one of its many parts causes it to stop functioning. That means gradual evolution would have been unlikely.

Evolutionists Argue ...


As with the vertebrate eye, scientists have discovered several intermediate steps leading up to the bacterial flagellum, Prothero said.

"There are semi-flagella in nature that are not as complicated as the bacterial one. All of this has been documented at great length, and [intelligent design proponents] ignore it over and over again."

5. Whales


Why Intelligent Design?


Darwin was ridiculed in his time for suggesting that small land animals could have transformed into modern whales, like the young sperm whale seen above in the waters off the Caribbean island of Dominica.

Whales "have a long generation time, and they don't have huge populations. They're like the worst-case scenario for trying to evolve structures rapidly," Luskin said. "To fix all the mutations needed to convert a little land mammal into a fully functional whale [in ten million years]--mathematically that's totally not possible."

Evolutionists Argue ...

But paleontologists have since shown that Darwin's guess wasn't that far from the truth. In the late 1970s scientists began unearthing fossils of "archaic" whales that were initially mostly terrestrial but that became more aquatic over time.

"We have the fossils showing how it happened," Prothero said. "Anyone who makes that argument is flat out lying about the fossil record."

6. Universal Perfection


Why Intelligent Design?


From what we know about the way the universe works, humans appear to inhabit a cosmic environment with variables that are remarkably well-suited for life as we know it (above, the famous "pillars of creation" as seen by the Hubble Space Telescope).

For example, the value of the gravitational constant--an equation that defines the amount of attraction between objects with mass--is just right for creating planets orbiting sunlike stars with lifetimes long enough for life to evolve. That must mean, intelligent design proponents say, the universe was designed by a supernatural being with life in mind.

Evolutionists Argue ...

The idea of a single finely-tuned universe shows a limited imagination, Prothero said. "There're lots of ways you can imagine a universe that is not finely tuned for us, but might be tuned for something else."

For example, some physicists have theorized that our universe is just one of many possible universes in an unimaginably large "multiverse." It should be no surprise then that, even without a higher plan, humans live in the universe that is hospitable to them.

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