Chicken teeth: Why we know evolution by natural selection is true, and Intelligent Design is hooey

Preface: I am not an evolutionary biologist. There are innumerable people who have doctoral degrees and such in this field of study, all of whom are better qualified to expound on the details of this subject than I. For those looking for evolutionary biology from the perspective of an actual biologist, there are innumerable resources out there, not the least of which is the new tome by famed Oxford biologist Richard Dawkins, The Greatest Show on Earth. Of course, I haven't seen any ID advocates who are evolutionary biologists either, so at the very least I'm as qualified as many of them to discuss the topic. Whenever I'm studying a science, I strive to understand its core concepts in their simplest terms. With this humble little essay, I hope to be able to give you, the reader, that same understanding.

Intelligent design is still at it

I would have thought that the Dover trial would have dealt a serious blow to Intelligent Design (ID), but it seems to have done so only in our ability to keep it out of public schools. The ID zealots are still at it in full force. Even CNN, perhaps in a sorry attempt to seem unbiased, stuck an essay by ID champion Stephen Meyer in its feature on the 150th anniversary of the publication of Darwin's landmark The Origin of Species. But ID should not be entertained as if it is a valid alternative to evolution, because it is not. It's pseudoscientific nonsense that belongs in the same annals of shame as Phrenology, Alchemy, and Astrology. We know that evolution is true, and that ID is a farce. But how?

ID advocates assert that the difference in the theories is one of inference. "Darwinists", as they call them, look at the genetic similarities between species and infer common ancestry; ID advocates, however, infer a common designer. The question then becomes twofold: what is the evidence of the efficacy of natural selection to produce functional complexity, and what is the evidence of design? Unfortunately for IDer's, the difference is not one of inference. Because if evolution is true, it will – like any scientific theory – make testable predictions that, if wrong, would falsify the theory. ID is pseudoscience precisely because of its inability to make falsifiable predictions.

To understand this, it's helpful to understand just what kind of predictions evolution makes, and how these predictions could, if shown to be wrong, falsify the theory. But first, a definition: many people (well... creationists, mostly) assert that evolution is "just a theory", as if "theory" means "guess" or "hypothesis" and should not be equated with "fact". However, this confuses the colloquial meaning of "theory" with the scientific meaning of the word. In science, a theory is a body of knowledge that explains observed phenomena. It must make falsifiable predictions. Facts are merely the observed components of a theory. For example, we know that bonobos and humans share over 98% of their DNA. That's a fact. The question is why do humans and bonobos have nearly identical DNA, and a proper theory not only must explain this phenomenon, but make testable predictions about future discoveries. 

Chicken teeth

It may come as a surprise that chickens have latent genes for producing teeth. Horses have latent genes for producing toes. Humans have latent genes for producing fully functional tails. Whales have latent genes for producing legs. Why? If we were designed to function exactly as we do, why do we have non-functional genes? Well, it turns out that in these animals' evolutionary ancestors, these genes were in fact functional. There's no reason for a whale to have a pelvic bone and a gene for producing legs, but they do because their evolutionary ancestors had functional pelvic bones and legs. But the IDer could always try to get around this argument by suggesting that God – err, excuse me, the "designer" – could have designed animals however it wanted. There could be imperfection and waste in nature, but that wouldn't refute design. It would just mean the design is inefficient. Or perhaps animals were designed to be able to adapt to different environments. After all, IDers and young-earth-creationists (YECs) don't deny the ability of natural selection to produce changes within a species – they call it "micro-evolution". But the key difference is not merely that evolution predicts wasteful genes, but it predicts specific types of wasteful genes according to an ordered hierarchy. We call this hierarchy the Phylogenetic Tree of Life.

The tree of life

The phylogenetic tree of life looks something like this:

Notice the branching of species. An example of very early branching would be vertebrates and invertebrates; thus we see these two kinds of animals – say, jellyfish and humans – much farther apart on the hierarchy of modern animals than jellyfish and starfish, or humans and apes. Accordingly, we should expect that jellyfish share much more of their DNA with other invertebrates, and humans share much more of their DNA with other vertebrates. And, of course, this is precisely what we observe. Evolution could have been (and could be) falsified if we find that animals on the opposite ends of the hierarchy shared more of the same latent DNA. Jellyfish, for example, do not have latent genes for producing pelvic bones. Humans do not have latent genes for producing stingers. All of the genes that these animals have, both functional and latent, are predicted to follow this precise ordered hierarchy.

Of course, the differences don't have to be that extreme. Humans do not have latent genes for producing reptilian scales, because the ancestors of modern reptiles and modern humans branched off long, long ago. Modern birds, however, do have latent genes for producing scales, and when we map their genes we find that birds share much of their DNA with ancient reptiles while we humans do not. If the IDer wants to get around this conundrum by suggesting that the designer could have designed an animal with certain degrees of inefficiency, the burden is on them to explain why we see genetic homogeneity among the specific branches of the phylogenetic tree that we do, and more importantly how this will affect what kinds of speciation we will observe in the future. Evolution predicts that if we find a new species of lizard and map its genes, it will share more of its latent DNA with extinct reptiles and modern birds than it will share with extinct mammals and modern primates – right along the ordered hierarchy of the phylogenetic tree. What such predictions does ID make? You guessed it – none.

Cecal valves and nylonase: evolution in action

It's often asserted by IDers that geological time scales – the thousands and millions of years between species – is a cop-out that prevents evolution from being observed. However, that is simply not the case. One of the best examples is the amazing evolution of podarcis sicula, a species of greenback lizards.

Contrary to popular myth, evolution does not predict or require one species to magically transform into another. Dogs will not give birth to horses, apes will not give birth to humans, etc. This is the fallacy of "micro-evolution" versus "macro-evolution" – two bogus terms invented by creationists who simply do not understand how evolution works. Evolution of new species occurs when a population becomes split, and the two populations are geographically isolated. The varying environmental pressures cause different genes to be favored by natural selection, and over time small changes accumulate until the two populations are so genetically different that, if merged again into one population, they would not be able to reproduce. You now have two distinct species where there was once only one.

The evolution of podarcis sicula is a profound, real-world example of evolution in action. In 1971, researchers introduced five pairs of these greenback lizards to the island of Pod Mrcaru from their native island of Pod Kopiste. 36 years later, these species were observed to have undergone profound evolutionary changes in response to their new environment. Their bodies changed shape to adapt to different food, their social structure changed, and – most astonishingly – they developed cecal valves, which are novel organs that slow the passage of food by creating fermentation chambers in the gut, where microbes can break down the difficult to digest portion of plants. Cecal valves are present in less than 1% of all scaled reptiles, and are absent in the greenbacks' source population on Pod Kopiste. If such dramatic changes can occur in just a few decades, it defies the imagination to ponder what kind of changes can occur over geological time scales.

Just as amazing as the rapid evolution of greenback lizards is the discovery of nylon-eating bacteria, which possess an enzyme specifically for the breaking down of nylon called, appropriately, nylonase. This is significant because before 1935, nylon didn't even exist – it's a synthetic material. Where did this gene come from? Did the "designer" just stick it in there? Of course not. It arose through mutation of the bacteria's genetic code, producing new species of bacteria that could make use of the material. Notably, this is a real-world example of something that creationists and IDers say cannot happen: the evolution of new information and increasing complexity of the genome.

Falsify this

The theory of evolution is applied in numerous everyday circumstances. Our understanding of genetic variation, natural selection and the hierarchy of speciation is what allows us to develop drugs to fight multi-drug-resistant bacteria, preserve the environment, and put food on our tables. What kind of uses might ID have? ID advocates have produced no such pragmatic uses for their theory. Unlike evolution, ID does not predict how and why genetic variation and speciation will occur. It is evolution's ability to withstand such falsifiable predictions, and to produce real-world uses for us, that make it a valid scientific theory. ID is nothing but pseudoscientific nonsense, a vain attempt by creationists to justify their narrow-minded religious beliefs in the face of overwhelming scientific evidence. I can't help but wonder what people find so threatening about evolution. It's truly remarkable, humbling, and awe-inspiring. And if science shatters our delusions of grandeur, has it really done us a disservice?

Practical applications of evolution:

Further reading:


Popular posts from this blog

Why Christianity is bullshit, part 1: The Bible is stupid

Why Christianity is bullshit, part 2: The Bible isn't true

There is no such thing as sophisticated theology