Last week I pointed out that the Bible provides no support for Ken Ham’s contention that massive numbers of species have formed following their departure from Noah’s ark 4500 years ago (YEC Biblical Evolution: I Have A Book That Says Otherwise). Now I’m following up with “observational” evidence from DNA sequences to test whether the patterns of sequence divergence fit the YEC hyper-evolution model.
Let’s review the claim of young earth creationists again. Ken Ham showed the following slide in his debate with Bill Nye. He explained that biblical creation proposes that there were only two of each kind on Noah’s ark and that a kind is best understood as being equivalent to a “family” as understood by taxonomists
Did all cats, dogs and elephants come from pairs of ancestors just 4500 year ago? Ham and other YECs like to show pictures of domestic dogs and all their apparent variety. Since everyone knows that domestic dogs are varieties of wolves we are supposed to be amazed at how much change can happen within a “kind”. Ken Ham then presupposes that this simple illustration can serve to explain all the variation within canines, felines or any other group of animals. He and other YECs seem to think that the formation of hundreds of new species is just the result of sorting out of genetic variation found in the representatives of each “kind” preserved on the ark.
But just how much variation is there within and between species? I have examined this question before (Of Kinds and Common Ancestors: Comparing Mitochondrial Genomes) but I thought I would do a few more analyses and present the data in figures rather than a table. I have used similar methods as described in that prior article. In brief, I have found a complete mtDNA genome (usually around 16,000 base pairs of DNA) and searched a database (NCBI) to pull out all other known mtDNAs that are similar. Then I have constructed a simply tree showing how similar each mtDNA genome is to one another. I have then scaled the trees so that the branches represent the same amount of difference on all the trees I show below. I am doing this to get at an apples-to-apples comparison of genetic differences between species.
The problem is that Ken Ham doesn’t seem to know much about genetic divergence or how to determine degrees of differences at all. In his talk, he showed a figure of domestic dogs and suggested that these dog varieties demonstrate that large amount of divergence of animals was possible in a short period of time (observational science to Ham) . Well, look at the figure above and let’s see how his observations match up to the genetic reality. I was able to get more than 800 complete mitochondrial genomes representing virtually every breed of dog. Included in these are multiple ancient dog genomes. These are dogs that were sequenced from bones that were hundreds to 10,000 years old. What should jump out at you is how incredibly similar all domesticated dogs are to one another. The mtDNA is a good proxy for their overall genetic divergence and so this is why geneticists would consider domestic dogs highly similar to one another.
The reason domestic dogs look very different morphologically is a matter of changes in a few developmental genes and a couple of genes for coat color, etc. You could say that the differences between dogs are really only skin deep. The vast majority of domestic dog DNA is identical to each other owing to their “recent” evolution from just a few wolves. Conventional evolutionary genetics predicts that domestic dogs would show very little divergence given they have only been separated from wolves for 10 to 20 thousand years. This is not considered enough time (generations) for large numbers of mutations to have built up in dog populations.
Now look at the differences between wolves, coyotes and then the foxes. This is a substantial amount of genetic divergence and this also reflects the millions of differences found in their nuclear genomes. These canines have thousands of different versions of genes and even differ in their number of chromosomes. In other words, domestic dogs may look different from one another but these differences are very superficial. And yet young earth creationists hold domestic dogs up as observational evidence that hyper-evolution can occur within “kinds.”
Now let’s take a look at cats and see how similar they are to one another. For cats species there aren’t as many complete mtDNA genomes, particularly for domestic cats. I am sure that all domestic cats would show no more differences from one another than the domestic dogs show or modern humans (see below). I have scaled this figure so that it is as close to an apples-to-apples comparison with the canines above. You can see that there is quite a bit of genetic divergence between the species of cats. For some perspective, given the amount of divergence observed and dates of fossils it is estimated that lions, tigers and leopards are thought to have split off from the other feline lineages, including domestic cats, some 10 to 15 million years ago.
What we are seeing here is very significant genetic differences among some cat lineages. Within a species like tigers there are differences that reflect different populations which have their own genetic history. Also, look at the hyena sequences. Hyenas have similar skeletal and other morphological characteristics to felines and here you can see that their mtDNA genomes also have similar sequences. However, young earth creationists insist that hyenas are a different kind and thus have no common ancestry with felines. But tigers and house cats do have a common ancestor?
There are only three species of living elephants but there are many complete mitochondrial genome sequences that have been obtained from fossils of mammoths and mastodons. What is really interesting about the mammoths in particular is that we have DNA sequences from mammoths that lived in Siberia, North America and even South America. And these samples are of different ages ranging from 10,000 years to 50,000 years old. The YEC model of origins would certainly predict that mammoths that spread themselves out across the Earth should show differences from one another because they evolved super fast early after the Flood.
What we see is that mammoths mtDNAs are remarkably similar. Now this isn’t surprising in an old Earth model of origins. Despite their being spread out geographically and over time, this is still a short period of time with respect to the life span of a typical species. There is variation among mammoths equivalent to a bit more than seen in people alive on Earth today.
Notice also how different the mastodon sequences are from other elephants. They have a very different tooth structure and other physical adaptions. Yet they lived at the same time and with mammoths in North America. If they really were both derived from the same two common ancestors on Noah’s ark then how did they come to be more different from humans and chimpanzees (see below for comparative data) and yet lived in the same environment? How could natural selection have sorted them into two very different elephants if they had the same resources and lived in the same place?
To give you some perspective on the degrees of mtDNA sequence differences in the prior figures, I did a quick analysis of 500 great ape and human mtDNA genomes. Again, I did this by taking a single human mtDNA genome and having the database (NCBI) pull the 500 most similar sequences and then drawing a tree in which the total number of DNA differences is represented as the branches connecting the individual sequences.
I have scaled the figure so the branches represent roughly the same amount of genetic divergence as seen in the canine, feline and elephant analyses above. From this similarity tree we can make several observations:
1) Modern humans are genetically very similar to one another – we truly are all one race! The genetic divergence of all modern humans (not including Neanderthals) is similar to that among wolves and domestic dogs.
2) Chimpanzees are a very diverse species and quite possibly should be considered at least two species. They may all look the same to you and I but the amount of genetic diversity among chimpanzees greatly eclipses that found among all humans including ancient lineages of humans (Neanderthal and Denisovan).
3) The difference between modern humans and Neanderthals is not very great compared to the total difference between humans and other great apes.
But here is the more provocative result of this simple analysis: Look at how much difference there is between humans and chimpanzees. It looks like a lot but then look above at the canines, feline and elephants, and you will see that the difference between the foxes and wolves, between a house cat and lion and a mastodon and mammoth is greater than the differences between humans and chimpanzees. It seems utterly inconsistent of Ken Ham to tell the world that they have no problem with foxes and domestic dogs having a common ancestor just 4500 years ago when mastodons and elephants, foxes and dogs, cougars and lions exhibit greater genetic divergence than chimpanzees and humans.
In the YEC evolution model, humans started out with eight individuals which would represent greater genetic diversity and potential and yet humans have populated the world in the same amount of time that canines, felines and elephants have had, and yet their total genetic diversity barely exceeds that of domesticated dogs much less the variation observed in these other “kinds.” What is the YEC explanation for why humans have experienced such incredibly low rates of change in this genome? I have no idea.
I think this just highlights the ad hoc nature of their proposals. They propose all canines from a common ancestor not because of any evidence that this has happened very recently but just so they can have only a pair of canines on the ark. But they haven’t thought through the consequences of such a proposal. Genetically it doesn’t make sense and it ends up creating more problems than it solves.