Gravity vs. Common Descent
I haven’t had any lively debate on my blog in a while, so I guess I need to be a little more inflammatory. So how about this to stir things up: THE THEORY OF EVOLUTION IS MORE CREDIBLE THAN THE THEORY OF GRAVITY! Yup - that’s right. You think I’m kidding? Keep reading…
The theory of gravity simply states that the force between any two objects varies directly with the product of their masses (m1 x m2) and inversely with the square of the distance (r) between them. The universal gravitational constant, G, is the factor that allows the force to be calculated if the masses and distance are known. Even though G can only be measured accurrately out to 3 decimal places, this powerful law can be used to predict the trajectories of moving bodies with great precision. Just think how amazing it is that NASA engineers can plan a rendezvous between a spacecraft launched from earth and an asteroid hurling through space at speeds over 2,000 mph some 100 million miles away. For most people, the universal gravitational constant is about as “universal” and as “constant” as anything else we know from science. In fact, few would arue or debate the law of gravity.
So it might come as quite a surprise to many folks that, mathematically speaking, we can be many times more certain of common descent than we can be of gravity. What was that? Yes - that’s right! To some, this might sound ridiculous. After all, we can directly observe and measure gravity! The law of gravity is testable and repeatable science! Evolution is mere speculation! Common descent is only a theory! How many time have you heard this? Now, in terms of being repeatable: gravity beats evolution. Sorry. There is simply no way to repeat something that takes 3.8 billion years to unfold and only happens once. But in terms of being testable and measurable, scientists can measure evolution.
So how well can evolution be measured? Well, we first need be clear on what the theory states? Simply put, the theory of evolution states that all species alive today descended from a single common ancestor. Therefore, the degree of similarities and differences between the species are due to the degree of “relatedness” between them. In other words, species that are more closely related, like cats and mice (both mammals), will have more in common than two species that are less closely related, like cats and frogs (mammals and amphibians). And all of these vertebrates are more closely related to eachother than they are to invertebrates, like snails or jellyfish. But all animals, both vertebrate and invertebrate, are more closely related to eachother than they are to plants, bacteria, or fungi. This ”branching” of all species from a single common ancestor produces a very specific pattern known as the “universal tree of life”.
In addition to constructing a “universal tree of life” by comparing similarities and differences in anatomy, we have an even better way to figure out who is related to who: molecular genetics. That’s right, DNA testing - it’s good for more than just settling paternity suits and convicting sexual offenders! Since DNA is always passed from ancestors to descendants, and there is no way for the junk DNA (unused genes that make up the vast majority of our genome) to be removed as it passes from generation to generation, the DNA of every species preserves a very detailed record of its evolutionary history.
The theory of evolution pre-dates the discovery of DNA by about 100 years. During this time, the 30 major biological groups that represent all living species were arranged simply by similarities and differences in anatomy - with a little help from the fossil record and biogeography (the geographical distribution of the species). There are 495,180,000,000,000,000,000,000,000,000,000,000,000 different ways that the 30 major biological groups can be arbitrarily arranged into family trees and there is absolutely no reason, apart from common descent, why one arrangement should be favored over any other. In fact, if the genetic similarities and differences between these 30 groups based on DNA testing revealed a different arrangement, then this would disprove common descent once and for all. In my book, this makes the theory of evolution very testable - more testable even than gravity, which can be measured with far less precision. Moreover, if there were no statistical correlation between the various family trees constructed by comparing DNA between the species, then the whole idea of common descent would go down in flames. In other words if different genetic markers followed different paths through the differnet species, then their distribution could not possibly be a product of common ancestry. This news would be huge!
Now, if common descent is false, and all species were created separately only a few thousand years ago, then there should be no statistical correlation between these various arrangements. In other words, none of the branches based on morphology should match any of the branches based on molecular genetics - since any relatedness between the species (or “kinds”) would only be an illusion. To be at least as certain of the “universal tree of life” as we are of the “universal gravitational constant” - we would only need for 18 of the 30 branches to match. But for all 30 of the 30 branches to match would be extremely coincidental. But in fact, this is the case. In other words, the “relatedness of the species” (ie: common descent) can be measured to an accuracy of 38 decimal places - 35 orders of magnitude more than the univesal gravitational constant! (See http://www.talkorigins.org/faqs/comdesc/section1.html).
So why is evolution still rejected by so many? Some reject it simply because scientists can’t fully explain exactly how evolution happened. While this is certainly true (natural selection can explain some things - but not everything), you might be surprised to hear that scientists can’t explain how gravity works either! The actual mechanism of gravity is still a mystery. There are several theories, from quantum gravity to string theories, but nothing has been confirmed. So if we must reject evolution, then we should at least be consistent and also reject the theory of gravity until either G can be measured to greater than 38 decimal places or until the actual mechanism of gravitational attraction can be fully explained.
-GJG