Author Topic: Molecular Evidence For Evolution  (Read 839 times)

Offline stromboli

Molecular Evidence For Evolution
« on: October 25, 2015, 02:49:15 PM »

If you’re just joining my story, here’s a quick catch-up. Once upon a time, I was an evangelical Christian. Although I was not a die-hard creationist, I considered creationists to be “my team” and evolutionists to be the godless “other team.” I trusted creationists because they were fellow Christians, and conservative ones at that. A decision my wife and I had to make forced me to investigate the creation/evolution issue more closely.

I hope the last few posts have given you a window into why I was appalled at how dishonest the creationist arguments turned out to have been. Now I’d like to give just a glimpse into the sort of arguments that I discovered on the side of evolution.

Most remarkable was the way completely independent lines of evidence all pointed to the same conclusion.  This graph is an example. It’s from the book that opened my eyes to the power of the evolutionary explanation for life, Scientists Confront Creationism.

I’ll walk you through it, and then I’ll say why I found it so compelling.

The horizontal axis extends backward in time. You’ll recognize the familiar geologic periods (or at least the Jurassic, if you’ve seen Jurassic Park). Radiometric dating has enabled us to estimate how far in the past each period occurred.

Based on the fossil record, scientists have determined when the common ancestor of certain pairs of organisms lived. For example, plants and animals last had a common ancestor about 1,200 million years ago. Vertebrates’ and insects’ last common ancestor lived near the dawn of the Cambrian, about 600 million years ago.

Now is where it gets really interesting. The vertical axis represents the amount of change in certain proteins, as measured in amino acid changes per 100 sites on the protein molecule. Of the four proteins represented, hemoglobin is probably the most familiar, so let’s look at that one.

Amino-acid changes to the hemoglobin molecule over time are shown in line second from the left. Straddling this line just below the label “Carp vs Lamprey” you see bounded bar. It indicates that if you compare the hemoglobin molecules of carp with those of lampreys, you’ll find about 90 changes per 100 sites. The bar is placed at about 500 million years ago because that’s where the fossil record shows the carp and lamprey diverged, at which point their respective hemoglobins could mutate independently.

The graph shows similar comparisons for several other divergences, and three other proteins.

Now here’s what’s remarkable about it.

First, notice how beautifully the bars fit on the lines. If the radioactive decay that has been used to date the geologic ages has been constant over time (and there is no reason to believe otherwise *), this would mean that the rates of protein mutation have also been constant. This validates evolutionists’ claim that the amount of change in a molecule is a reliable molecular clock: mutations occur randomly at a constant rate, so the accumulated mutations indicate how long mutations have been occurring.

But wait! There’s more!! You no doubt noticed that the slopes of the four lines differ: histone IV has changed hardly at all, while the others have changed more rapidly. Why is this? It turns out that these molecules have evolved at a rate proportional to the degrees of freedom they have in fulfilling their function. As Scientists Confront Creationism explains, “…histones are a class of proteins that are bound to the DNA in cells that possess a nucleus. … Any change in histones could therefore have a destructive effect on the integrity of cells. Thus, the histones of organisms as diverse as peas and cows are almost identical.” Hemoglobin, by contrast, only carries oxygen from lungs to cells and ferries carbon dioxide on the return trip. Those are important functions, to be sure, but there are many ways to solve those problems without jeopardizing the integrity of the cells. Therefore, the evolution of hemoglobin has been less constrained and it has obliged by evolving more rapidly.

Thus, the graph shows three independent modes of inquiry coming together in perfect synchronization under the evolutionary model:

Radiometric dating.
The fossil record.
Molecular clocks.

This is all from just one graph in one chapter of Scientists Confront Creationism. The book is filled with this sort of interlocking evidence from many more independent disciplines.

Could a Designer have created carps, lampreys, mammals, birds, reptiles, fish, insects and plants with just the sort of genetic divergence shown on the graph, and apparent common ancestors at just those apparent times — when in fact the organisms are not related by common descent, and their apparent age as measured by radioactive decay of the rock layers in which they are found is just a fiction? Of course he could have.

He could also have created the universe 10 minutes ago, including your false memory of what you had for dinner last night.

For that matter, why not believe this is all a dream, and you’re the only being that exists?

You may not take the last suggestion seriously, but it’s hard to disprove; a 10-minute-old universe may seem only slightly less plausible, but is equally frustrating to argue against; a Designer that creates things to appear as they are not is actually quite plausible to some people but distasteful to most; and most scientists seek completely secular explanations, but that is not in the cards for religious people. So why choose one outlook over the others? Are all of these positions just a matter of faith? That will be the subject of the next post.

*  — Creationists dispute the constancy of radioactive decay, because they must. The Institute for Creation Research and the creationist organization Answers in Genesis collaborated on a study called Radioisotopes and the Age of the Earth, or RATE that claimed “There is evidence that nuclear decay rates were grossly accelerated during a recent catastrophic episode or episodes” (i.e., Noah’s Flood). The equally Christian, but non-creationist, American Scientific Affiliation counters that the heat produced by this alleged million-fold increase in radiation would have vaporized the Earth, and even if the Earth survived, Noah and his passengers would have been killed by the radiation itself. They quote the RATE group as acknowledging these problems, but being “confident that these issues will be solved.” I suppose you can solve any problem with a miracle, right?

Molecular mutation and radiometric dating. You can also add that sedimentary layering, the mitochondrial clock, ice core dating and a few other ways of determining the time frame of evolutionary change and the age of the earth.