Evidence. Been a while since I did a post on this topic. Trashing IDist arguments doesn’t count.
Lots of words have been used to describe the evidence in favour of evolution, and they range from “mountainous” to “non-existent” depending on whether you’re listening to biologists or dentists (no offence to the many wonderful, rational dentists out there, especially the ones who are putting braces on my teeth this Thursday. [cowers]). There’s also some rather extreme variety in the contributing fields: everything from molecular and genetic studies to palaeontology and geology to physical and behavioural studies of living creatures. I should remind myself to write more on this subject in the future.
But the most compelling line of evidence for common descent as a whole isn’t anything in particular. I can go on until the cows come home and start eating the furniture and generally stinking up the place about how fossils and molecules and physiology and taxonomy and radiology and retroviruses and genetics and reality make evolution denialism about as rational as believing that Elvis is still alive, and he faked his death to elope with Bigfoot to the high mountains of Nepal, where they live with the 17th re-incarnation of the Dalai Lama, who came back in time to convince the Great God Thor to grant Van Halen immortality so he could follow in Aerosmith’s footsteps and save the world from the Mayan islamosocialist zombie apocalypse in Dec 2012.
And it’s all Obama’s fault for faking the Kenyan moon landing.
True story. Anyway, where was I?
I could go on about all the individual lines of evidence until [insert ridiculous hypothetical here], but the most compelling evidence isn’t any of these on their own: it’s all of them together. It’s the nested hierarchy, also known as the Tree of Life, itself.
You see, a major prediction of common descent is that it inevitably forms a nested hierarchy. Due to the random nature of mutations, and the immense variety of “everything that is biologically possible”, it’s practically impossible to achieve the same thing in exactly the same way twice. What this means is that an identical feature in two separate species, whether it be molecular, physical, skeletal or behavioural, is a strong indicator of common descent. If a third species doesn’t share the same feature as the first two species, then that indicates its common ancestor is earlier on the timeline.
So… say two animals have very similar keratin beaks, while a third animal does not. According to the theory, it’s a fair bet that the two beaked animals are more closely related, and share a more recent common ancestor, than either of them do with the beakless wonder.
This is where I lose any denialists who may or may not be reading along. You see, when a denialist reads the above sentence, a special oil-cavity in their skull relaxes, dousing their brains in contrary oil. This leads to them pointing out that I am stating assumptions like “identical features are a strong indicator of common descent” as facts. They then demand observable, demonstratable evidence that the two beaked creatures are in fact related, or else they feel justified the rest of my argument. (if you’re an anti-evolutionist and this doesn’t properly represent your reaction, feel free to leave a comment. 🙂 )
For the record, evidence is a fine thing and should always be demanded when unfounded assumptions are expressed as facts. However, in this particular case, I am not making an assumption: I am stating a logical prediction of the theory. If the theory is right, this prediction will be true. If the prediction isn’t true, the theory isn’t right. And if the theory is wrong and we really were spoken into existence by God/deposited by aliens/travelled here from another dimension/sneezed out by the great green Arkleseisure, then the prediction has no reason to be true. And if the prediction is right… okay, I’ll stop being redundant. You get the idea.
This all leads us quite elegantly (or it would, if I had any elegance at all) to the question: is the prediction true? How do we check that our beaked creatures do in fact share a more recent common ancestor than they do with the third, un-beaked creature?
As it turns out, that’s easy. We use a different set of features to re-construct the graph… say, hollow bones. Hey look! It matches! This lowers the probability that it was just a fluke. Then we re-construct it from another set of features… say, fused vertebrae … and another… lack of teeth… and another and another and another…
With living creatures you can do this with all their genes as well, as well as a huge variety of physical and behavioural features, and rather than comparing two or three creatures, you can do it with ALL OF THEM: every organism on the planet, including the fossilised ones. That’s hundreds of thousands of traits being compared across billions of species: not a shoddy test by anyone’s standards, and certainly not the dismissive hand-wave anti-evolutionists love to characterise evolutionary science as.
And EVERY. SINGLE. TIME, you end up with the same graph. This graph:
The story behind this particular example: “This tree is from an analysis of small subunit rRNA sequences sampled from about 3,000 species from throughout the Tree of Life. The species were chosen based on their availability, but we attempted to include most of the major groups, sampled very roughly in proportion to the number of known species in each group (although many
groups remain over- or under-represented). “
All it would take is one feature, on one Species, that doesn’t fit this graph: a mammal with avian feathers, a classic style minotaur or a chimera or a mermaid or a Pegasus (pegasii? pegaseuss?), or maybe Ray Comforts famously mockable crocoduck… and the entire edifice shakes, and the discoverer get’s worldwide recognition. Yet we’ve never, ever, found creatures like that except in myth and legend. Even with the massive amount of biodiversity on earth, every species living or dead we’ve ever discovered fits into and confirms this one graph: sometimes it has to be turned around a bit first because convergent evolution often has a few surprises lying in wait in the long grass, but it always fits. Every bloody time.
That is why evolution denialism is not just a matter of religious opinion, or of interpreting the same evidence differently. Denying that mutation and natural selection are the source of biodiversity on earth is like denying that gravities influence on matter is the source of planets orbiting the sun.
I have never seen any other hypothesis or theory that explains the prevalence of the Nested Hierarchy across every species and in every feature of biological physiology. “Common designer” can only hand wave so much.
“The Kenyan moon landing was faked. It wasn’t really set in a studio in Texas, like the government would have you believe. They secretly filmed it on the moon.”