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SKEPTOID BLOG:

Providing evidence for evolution

by Chad Jones

February 16, 2013

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Donate Last week I pointed out some common misconceptions about evolution and arguments that are often used to support creationism. This week I would like to share some of what I feel to be the strongest evidences for evolution. I feel like too often in debates about evolution the focus seems to be on refuting creationism instead of correctly presenting evolution - and the science is really awesome. With the evidence I present here I seek to answer the following questions:

What is the fossil evidence for evolution?

What can we learn about evolution from living animals?

Does evolution present any testable predictions?

What is the fossil evidence for evolution?

One of the common arguments against evolution is "where are the transition fossils". This is perhaps the weakest of all arguments against evolution. The transition fossils (or casts of the fossils) are available in every reliable natural history museum. Wikipedia has an extensive list of transition fossils. These fossils include the human evolution of Australopithecus to Homo Habilis to Homo Erectus to Homo Sapien. They include evolution of invertebrates to fish. They even include the evolution of insects.

The fossil evidence is extensive, and the argument that we don't have fossil evidence is tired. Creationists quickly say things like "just show me the transition fossils" or "where is the missing link", but we actually have quite a bit of fossil evidence. Just this last week Dr. Steven Novella wrote a great article on feathered dinosaurs - an excellent example of transition fossils.

Unfortunately, each time new evidence of this type is presented creationists treat the new fossil like the hydra from greek mythology - finding one transition fossil just creates two new transitions whose fossils haven't been found yet.

What can we learn about evolution from living animals?

The Laryngeal Nerve

An interesting evidence for evolution is the laryngeal nerve - the nerve that supplies motor function and sensation to your larynx. If you were to design the nervous system in an obvious way the laryngeal nerve would leave the spinal chord somewhere in your neck and travel directly to the larynx. Instead, the laryngeal nerve leaves the spinal chord at the neck, travels down into the chest, wraps around an artery leaving the heart, and then travels back up the chest, up the neck, and finally ending at the larynx.

This odd path is even more exaggerated in a giraffe, where the nerve travels 15 feet out of the way to wrap around the heart and return to the larynx - only a short distance from where it originally left the spinal chord.


So why does the nerve take such a convoluted path? Evolutionary theory describes an ancestor to all vertebrates much like modern fish. The same nerve in fish takes a much more direct path from the spinal chord to the larynx. As evolution progressed, the laryngeal nerve was caught on the wrong side of the heart. With each generation, natural selection lengthened the neck and with it the laryngeal nerve.

Ensatina

A second modern day example of evolution is the Ensatina of California. These salamanders live in a ring around the Sierra Nevada mountains and give an interesting example of speciation. Where does one species end and a new species begin? A simple definition is that two animals are different species if they are unable to breed fertile offspring.

In this example, the salamander with the red label interbreed with the salamander with the yellow label, the yellow interbreeds with the blue and orange, and the blue interbreeds with the pink. However, the pink does not interbreed with the red. It is safe to say that the pink and the red salamanders are different species - but where did the speciation occur? Evolution does not happen in large jumps. It happens slowly, with changes every generation.

Does evolution present any testable predictions?

One important qualification of a scientific theory is that any new idea must provide some testable hypothesis. How can we know that we aren't just deceiving ourselves if we can't test the ideas we've come up with? So, does evolution provide any testable predictions?

Human Chromosome 2

Chromosomes are highly condensed structures made of deoxyribonucleic acid (DNA). DNA, of course, being the key building block of all life. DNA stores our genetic information.

Human chromosome 2 gave a testable hypothesis for evolution. If apes and humans truly have a common ancestor, then we should have the same number of chromosomes. As it turns out, we do not have the same number of chromosomes - humans have 23 pairs and apes have 24 pairs. This is actually a big problem for evolution as a viable theory. If at any point a chromosome was spontaneously lost or gained it would result in serious consequences (either miscariage, or a phenotypic disorder like Down Syndrome or Turner Syndrome). Evolutionary biologists predicted that at some point a chromosome fusion happened (that is, two chromosomes combined into one large chromosome). In this way, no genetic information would be lost and a difference in chromosomes would not disprove evolution.

As it turns out, human chromosome 2 is a fusion of two chromosomes. There are four telomeres (which begin and end a chromosome) and two centromeres (which are found at the center of a chromosome). Of course, showing that human chromosome 2 is fused is not enough to prove that we have a common ancestor with apes. However, this evidence is strongly supported by the identification in chimpanzees of exactly which chromosomes were fused to create human chromosome 2. To me this is a home run for the theory of evolution.

Conclusion

There is strong evidence for evolution, but just as my previous post was in no means a complete list of all the arguments used to refute evolution, this post in no way contains all the evidence. In fact, it's probable that I left out some of the most compelling evidence (and I'd love to hear them in the comments). However, in writing this article I chose the evidence that I see as the most compelling.

by Chad Jones

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