Although the Theory of Evolution is one of the most tested, well supported, and accepted theories in science, it still happens quite often on this site that people get into arguments about whether Evolution is actually even true or not. This tends to happen in the various religion threads like clockwork.
The purpose of this thread is to present and compile informational links, videos, and pieces of evidence for why Evolution is true, and to be able to use this as a resource in future discussions. Instead of getting into yet another argument about whether there is or isnt evidence supporting Evolution, you can now just link to this thread and be done with it.
(If you run across any new pieces of evidence or interesting resources, please PM me and I can include it here at the top of the thread.)
What is a scientific "theory" and how is it validated?
A theory in science is an explanation of some system or aspect of the natural world. A theory usually explains how individual facts and natural laws fit together, makes testable and falsifiable predictions about what that system should look like, and is generally very well substantiated by observations and experimentation. When a scientific theory becomes an "accepted" theory (i.e. it gains scientific consensus) that theory is pretty much understood to be a fact and a correct explanation of how that aspect of nature works. Examples of such theories are Quantum Mechanics, Einstein's Theory of Relativity, the Germ Theory of Disease, Plate Tectonics, and of course Evolution by Natural Selection.
In science, theories make predictions, those predictions are then tested, and either the tests support the theory or contradict it. If they support it, we keep testing in new ways until we have a very high level of confidence in the theory. If any observation or experiment contradicts the theory, that theory is discarded. All it takes is one of a theories predictions to shown false for a theory to be rejected.
Also, here's a great video explaining the difference between the words "law", "hypothesis", and "theory" in science:
What is the Theory of Evolution?
Evolution says that all species on Earth are linked through common ancestors back to a first organism. When organisms reproduce, small random changes are introduced that lead to new and different traits. By the process of Natural Selection, those traits that allow an organism to reproduce more are then more likely to be represented in the next generation. Through this process beneficial genes are passed on and harmful ones die off. So, while changes at the level of the DNA are initially random, the selective process of the environment causes organisms to adapt.
The strength of Evolution as a theory is that its predictions have been tested and supported over more than 150 years by many different and independent types of evidence, from DNA to fossils to geographical distributions and comparative anatomy. And, no one has yet found any evidence that contradicts Evolution. If they ever do there's a Nobel Prize waiting for them. =)
What predictions does Evolution make?
- we should find simpler organisms in the fossil record the further back we look
- traces of the relationship between species should be observed in their DNA
- changes from species to species should be gradual (i.e. there should be transitional forms)
- fossils for the first of a species should be found geographically where it's predecessors would be located
- species should be seen to become more well-suited to their environment over time
- an old Earth... at least old enough for all the changes we see to have taken place
Links to general information and evidence for Evolution:
Wikipedia has two very comprehensive pages on Evolution in general as well as the evidence for common descent.
Talkorigins also has a very good page with tons of evidence for common descent:
Another page with more evidence for biological evolution:
Videos about Evolution:
This is a well-produced and short video mostly focusing on the evolution of whales.
This is a very good video that covers a lot of evidence for Evolution. Definitely watch this!
Here's another video with more animations and meant more as a general explanation of how Evolution works:
Evidence supporting Evolution:
Here I will be posting individual pieces of evidence for Evolution with a general explanation of it as well as links to more comprehensive information. I'll initially post a few and then grow this section over time.
One of the clues that gave Darwin the idea of Natural Selection was the variety of Finches he found on the Galapagos. They were mostly very similar birds, but with a lot of variation in beak size and shape. Altogether there are 14 species of finches associated with Darwin. What he concluded was that all these species were just variations caused by initial groups of finches from nearby South America that flew to the islands a long time ago. Because of the distance between the islands, the finches couldnt move from island to island, so they were isolated and eventually over time evolved to be better suited to their environments. This was one of the first and it's still one of the best pieces of evidence for Evolution by Natural Selection.
If you see above in the "predictions of Evolution" section, you'll see that Evolution predicts that we should see traces of our common ancestry in the DNA of us versus other animals. So, if chimps and us evolved from an ancestor, we should see common code in our DNA. Do we?
Well, yes, of course we do. We can not only see the same code, but also differences... with more differences in more distance relatives as Evolution predicts. In fact all the evidence from DNA confirms Evolution. But, there's a difference in our DNA versus that of the "great apes".
All great apes have 24 pairs of chromosomes, but humans have 23. Why is this? If humans and apes are related through a common ancestor, then either humans lost a chromosome sometime in the past, or apes gained one. How would we know what happened and when? Will this shoot down Evolution or can it support it?
As it turns out, chromosomes have markers in the middle called Centromeres and markers at the ends called Telomeres. By studying the DNA of humans and apes we've found that on the human #2 chromosome there are matching Telomeres and Centromeres that show that chromosome #2 was originally two separate chromosomes that were merged into one.
When looking at the DNA of apes and humans, we can see that they are mostly the same code... with chimpanzees being our closest relatives. Because of that we can even look at their chromosomes and know which 2 chromosomes from our common ancestor were initially merged to form our #2 chromosome.
In this video Ken Miller talks about this fact and how it was presented in the famous case that shot down Intelligent Design in schools, with the judge ruling that Intelligent Design was just Creationism pretending to be science.
Evolution predicts that the fossil record should show remains of transitional forms between current species and those that came before. For humans, we now have a very good record and collection of fossils and skulls that paint this picture. From our current form of Homo sapiens to our predecessors Homo erectus and back through Australopithecus afarencis, we can clearly see the progression of brain size and how the skeletons changed over time. The fossil record is a beautiful illustration of what Evolution predicts and really cant be explained in any other way that makes sense.
I also found this very good series of blog posts from a paleontologist (who is apparently a theistic evolutionist) discussing the human fossil record. It's a religious site, but the information seems pretty good and the author looks like he's reputable.
Lastly, this very interesting video on evidence that you can find right in the human body.
And here's an interesting video that talks about why eggs are shaped the way they are, and a nice example of how Evolution works to solve problems: