Ashwin on Common Descent

[swamidass (S. Joshua Swamidass)]

1. The functional/design difference between humans and chimps is GREATER THAN the functional/design difference between mice and rats.

However, this leads us a surprising fact of nature…

2. The genetic difference between humans and chimps is LESS THAN the genetic difference between mice and rats.

Notice, this is NOT an argument that reduces to “humans and chimps are sooooo similar!” No, this is a comparative statement, for which I have not even specified how we are measuring genetic differences. Really, any generic genome-wide measure of differences will do. They will all give the same relative answer. This is a robust finding.

Which then brings us to the big question…

3. Why is it that #1 did not correctly predict #2? Why is it that the large gap in functional/design differences between humans and chimps did not translate into a larger difference in genetic differences (comparative to mice and rats)?

That is the fundamental puzzle of nature. Evolutionary science, making use of common descent, provides a mathematical answer to this puzzle.

4. It tells us that the formula D=TR should approximately hold for genetic differences. The genetic data does, in fact, follow this approximate pattern. For many types of differences, we can measure D, T, and R independently and it matches this formula.

5. The formula D=TR does not explain functional/design differences, which do not work by this formula at all, and can change at much different rates.

That is the point of the argument. The genetic features change in a regular predictable way, but the design/functional features do not change in a regular predictable way. That is why there can be such a large discrepancy between the two, as we see in this case.

6. So this explains why we see humans/chimps so similar genetically, but functionally so different, and mice/rats the opposite. No other known design principle explains this curious feature of the world, and many many others like it.

So that is why we take common descent to be a rock solid finding of genetic science. That is also why the difficulty in mapping phenotype/forum/function to genetics does not undermine, but actually bolsters, the argument. Phenotype/forum/function does not change at a regular rate, but genetics does. That is why we see the discrepancy. That is why it scientifically looks like common descent. Common descent is the plain reading of genomes.

---

@swamidass

hat means it might be warranted to believe special creation in theology, but science is still going to teach common descent within the confines of science.

I understand this… though u will not confine myself to the basic assumption of natural causes… Because I don’t see the assumption as true in all cases (I.e I believe God can intervene miraculously).

Fine. Do that, but ONLY if you make that leap outside of science. I’ve already granted that can be legitimate outside of science. The case for common descent is only about what we can say in science in the language of science.

Now, it is legitimate to wonder if God intervened at points in a process of common descent to make special species from existing species. Maybe that is what happened. There is no strong evidence for or against this. Practically speaking, this is no different than inspiring mutations in common descent, or “god guided” evolution as @gbrooks9 likes to call it. You can certainly take that path.