Evolution is the foundational theory of biology that explains the diversity and story of life through slow genetic changes in populations over time. The story of evolution unifies all living creature as cousins within the same family tree, separated only by forces of natural selection over 3.7 billion years. As biologist Richard Dawkins points out, “Every one of the millions of species of animals shares an ancestor with every other one.”

First proposed in 1859 by Charles Darwin in his On the Origin of Species, the theory of evolution is now regarded as scientific fact. It didn’t have to be true, but 150 years of evidence and research has proved it to be. Just like the theories of the heliocentric solar system, the round earth, and continental drift it began in ridicule and was later confirmed as fact. Yet, more than 40% of Americans deny that humans evolved from other animals. Clearly we have some explaining and evidence to present.

First, the key to evolution is the systematic increase or decrease in the prevalence of certain genes in the gene pool. Second, chimpanzees don’t turn into humans. Instead gradual genetic changes are selected by forces in nature and thus survive in greater number in successive generations. Over vast periods of time these changes in genes lead to divergent branches on the tree of life with some surviving and some not. Humans and chimps shared a common ancestral population that accumulated generation after generation of favorable change.

There are several great resources out there that can do a better job than me of explaining evolution. Here are a few:

So What is the Evidence?

1. Fossils – The fossil record is abundant in examples of transitional fossils that demonstrate the slow evolution from fish to amphibians (i.e. tiktaalik) , from reptiles to mammals, reptiles to birds, land mammals to sea mammals, and the even the emergence of man. Considering the odds of fossils even forming it is remarkable that we have so many. The running joke is that every time scientists fill a gap in the fossil record with a missing link someone cries “look there are now two gaps!”

2. Geological succession – The age and placement of fossils within the geological record matches the predictions and evidence of evolution perfectly. When asked how one could disprove evolution J.B.S. Haldane famously said “fossil rabbits in the precambrian.” We never see human fossils with dinosaurs or other mismatches. The geologic record matches evolutionary history.

3. Geographic divide – Even with no fossils the evidence is from surviving animals is still overwhelming. Why are there no penguins in the arctic? Why are certain species only found on certain islands or continents? Species are distributed around the world based off their evolutionary history. For example the distance of tens of miles among Galapagos islands and the 600 miles to the mainland would lead you to suppose the islands would have species fairly similar to each other yet different from the mainland. That is exactly what we find.

4. Vestigial organs – Organs and features of ancestors that lose functionality still survive among many species. They seem without purpose unless explained through evolution. Flightless birds (i.e. ostrich), permanently covered eyes (cave salamander), or even defunct tails in humans are examples of past useful features that changed or lost use.

5. Genetic similarities – The entire great diversity of live use the same small set of amino acids to build proteins and the same four building blocks to build DNA. Richard Dawkins explains, “Not just the genetic code itself, but the whole gene/protein system for running life, is the same in all animals, plants, fungi, bacteria, archaea and viruses.” Further, analysis shows that humans share 98% of our DNA with chimpanzees and even 60% of our DNA with a fruit fly. Further, the skeletons of all mammals follow the same structure and the same 28 bones are found across all of them.

6. Observable divergence – Even though evolution acts most impressively over millions of years we do have examples of quicker change. First, through artificial selection, Dimitri Belyaru bred foxes for tameness in the 1950s and after 30 generations 80% were in a new category. Second, scientists transplanted lizards of Pod Kopiste to Pod Mrcaru in 1971 and by 2008 they returned to find divergence. Third, Richard Lenski at Michigan State experimented with 45,000 generations of E-coli in 12 separate lines showing proof of evolution including: random mutation followed by non-random natural selection, adaptation to the same environment independently, successive mutation building on predecessors, reliance of genes on others for effect, and new information entering the genome without the intervention of a designer.

7. Human changes – Evidence of changes in humans is observed within the context of evolution. The growth of the human brain has led to increasing death of the mother during child-birth. Chronic back problems have emerged from our “recent” conversion to upright mobility after millions of years on four legs. Humans shed their hair to allow two million sweat glands to cool the body while hunting for food. Also, people near the equator developed dark skin to block out the sun and protect folate reserves whereas people far from the equator developed light skin to absorb sunlight and sufficient vitamin D.

8. Un-intelligent design – There are certain biological realities that can only be explained through evolution. For example, the vas deferens loops the long way around the ureter to the testes. Likewise, the laryngeal nerve in a giraffe travels several meters down and up the neck when a few centimeters would do. These instances show that improvements accumulated to existing materials instead of starting from scratch with a designer. Dawkins puts it plainly, “the dolphin’s blow-hole goes to great length to correct a problem that would never have arisen at all if only it breathed with gills, like a fish.”

The most powerful evidence really is that the entire collection of fossils, migration paths, genetics, vestigial organs and more tell the exact same story. There is complete harmony with the predictions of evolution and observed experience, experiments and evidence.

Common Misconceptions

Here are a few common objections I’ve encountered as well:

I can’t believe it is all random. While the variety in the genome emerges through genetic mutations over time. Evolution is NOT random because it is guided by natural selection. The constant struggle to grow taller branches, run faster or see better is what ultimately enabled simple organisms to evolve into the wondrous world we see. While there is not an intended outcome (i.e. humans) evolution is far from random.

Evolution can’t explain where life came from! You’re right, it only explains how life changes over time into the vast variety of species we find today. There are other ideas of how life originated, but that is beyond the scope of evolution.

Doesn’t there have to be design involved? Some people claim that certain organs are irreducibly complex like the eye or bacterial flagellum, but that idea has been disproved. Complex things can emerge without a designer. Just think of a flock of birds or the free market appearing to have a conscious guiding hand while simply being the result of smaller individual forces.

Doesn’t evolution degrade humans and undermine morality? Even if it did encourage immorality that wouldn’t mean evolution was false. While evolution is not goal oriented, the human faculties and moral intuitions are a product of the time intense process. It explains the world as it is, however beautiful or harsh. We are a part of this world and responsibility as a member in the family of life.

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