by Casey Luskin (originally written in Oct. of 2005, updated in 2008
Dr. Kenneth Miller was the leadoff hitter for plaintiffs last week in the trial over ID in Dover. Amidst other things, Miller's testimony was aimed at making a case that the Neo-Darwinian hypothesis is as well-supported as gravitational theory. It was my understanding that this trial was about whether or not Dover had violated the First Amendment by mentioning to students that some book in the library advocated intelligent design. So I was a little confused as to why it was relevant for Miller to give us all a lesson in evolutionary biology. Nonetheless, this article will respond to Dr. Miller's arguments that evidence for fusion in human chromosome #2 demonstrates that humans share a common ancestor with living apes.
According to Neo-Darwinism, humans and extant apes supposedly share a common ancestor. During Dr. Miller's testimony supporting the theory of evolution, he discussed how human chromosome #2 has two centromeres, which are the central - attachment points used for pulling a chromosome to one end of a cell during mitosis. Chromosomes normally only have one centromere, but human chromosome # 2 looks like two chromosomes were fused together within its interior because it has two centromeres (or at least, it has one normal centromere, and another region that looks a lot like a centromere elsewhere within the chromosome). Miller further noted that human chromosome #2 has a section where there are two telomeres, structures normally at the tips of chromosomes, which are found in the middle of chromosome #2. Essentially, these two telomeres are oriented in a way that it looks, genetically speaking, like the ends of two chromosomes were fused together.
I am more than willing to acknowledge and affirm that Miller provided good direct empirical evidence for a chromosomal fusion event which created human chromosome #2. He claims this evidence strongly supports his view that humans and chimps share a common ancestor, because humans have two fewer chromosomes than chimp, and Darwinian evolution predicts this fusion evidence. But his argument raises two crucial questions:
(1) Is his chromosome fusion story good evidence for Neo-Darwinian common ancestry between humans and apes?
(2) Does Dr. Miller's hypothesis perhaps pose problems for a Neo-Darwinian account of human genetic history?
As will be discussed below, the answer to Question (1) is "No" and the answer to Question (2) is "Yes."
Evidence for Fusion in a Human Chromosome Tells you LITTLE TO NOTHING about whether Humans Share a Common Ancestor with Living Apes
Usually Darwinists argue for human-ape common ancestry based upon alleged "shared errors" in human DNA and ape DNA. But the chromosomal fusion evidence is not a “shared error” argument for human / ape common ancestry, because apes do not have a fused chromosome. The human chromosomal fusion argument focuses on a fusion event that is specific to the human line, and therefore provides a highly limited form of evidence for human / ape common ancestry.
All Miller has done is documented direct empirical evidence of a chromosomal fusion event in the human line. But evidence for a chromosomal fusion event is not evidence for when that event took place, nor is it evidence for the ancestry prior to that event.
To be more specific, the fusion-evidence implies that some of our ancestors likely had 48 chromosomes. But Miller has not provided any evidence that the individual with 48 chromosomes was historically related to modern apes. (I grant that our chromosome #2 has banding patterns similar to two ape chromosomes, but given that our chromosome structure is generally similar to that of apes anyways, it is not a stretch to assume that any 48 chromosome ancestor of modern humans might have also had a chromosomal scheme similar to that of apes, regardless of whether or not that individual was related to apes. Claiming that banding pattern similarities is evidence of common ancestry with apes simply invokes the “similarity = common ancestry” argument, and thus begs the question.) It is entirely possible that our genus Homo underwent a chromosomal fusion event within its own separate history.
Under Neo-Darwinism, the common ancestor of humans and apes is thought to have lived about six million years ago. But under Miller's account, it is entirely possible that this chromosomal fusion event happened in a human population only 10,000 years ago, in a population that has no relation to living apes. In such a case, this chromosomal fusion event thus needs not have anything to do with making us human-like as opposed to ape-like. Clearly this chromosomal fusion event could be extremely far removed from any alleged ancestry with apes.
In essence, we don't know that this chromosomal fusion event happened on a line which leads back to some alleged common ancestor of apes and humans. All we know is that this fusion event happened in the line that led to you and me. Whether that line has common ancestry with apes is a separate question which cannot be answered by this fusion evidence.
All that evolutionists have claimed is that this fusion event occurred after the split that led to humans, so it occurs only in the human lineage. Evidence of a chromosomal fusion event is not evidence that our line leads all the way back to apes.
Given that we had a 48-chromosome ancestor, we don't know if our 48-chromosome ancestor was an ape or not. For all we know, our 48-chromosome ancestor was a part of a separately designed species, as fully human as any person you might meet on the street today. There is no good reason to think that going from a 46-chromosome individual to a 48-chromosome individual would make our species more ape-like.
This is explained in figure 1 below:
Figure 1. This animated gif shows how even if the empirical genetic evidence mandates a chromosomal fusion event, this doesn't tell you anything about whether or not humans share ancestry with apes. The "Separate Ancestry" slide shows that the chromosomal fusion event may have simply taken place in a separately-designed basic type which, initially, had 48 chromosomes. The "Common Ancestry" slide shows how the chromosomal fusion event may have also taken place in a line which led back to a hypothetical common ancestor of humans and modern apes. The point is that all we have is evidence for a fusion event, but that fusion event is equally compatible with either separate ancestry from apes, or common ancestry with apes. The fusion event itself does not provide any independent evidence for common ancestry with apes. To argue that it is evidence for common ancestry requires special pleading.
Miller's "prediction" of Neo-Darwinian evolution is not a hard prediction of his theory: if common ancestry is true, Miller predicts that there must have been a fusion event. But the converse is not true. The presence of this fusion event in no way requires that common ancestry is true.
It only gets worse for Neo-Darwinism
Under Neo-Darwinism, genetic mutation events (including chromosomal aberrations) are generally assumed to be random and unguided. Miller's Cold-Fusion tale becomes more suspicious when one starts to ask harder questions like "how could a fusion event get fixed into a population via random and unguided processes, or how could it result in viable offspring?" Miller's account must overcome two potential obstacles:
(1) In most of our experience, individuals with randomly-fused chromosomes or extra chromosomes can be normal, but it is very likely that their offspring will ultimately have a genetic disease. A classic example of such is a cause of Down syndrome, where an individual has an extra chromosome #21.
(2) One way around the problem in (1) is to find a mate that also had an identical chromosomal fusion event or chromosomal splitting event. But this would require a rare mutant finding a mate with identical traits. Valentine and Erwin explain that the odds of rare-mutants finding mates with identical traits are highly unlikely:
"[T]he chance of two identical rare mutant individuals arising in sufficient propinquity to produce offspring seems too small to consider as a significant evolutionary event."
(Erwin, D..H., and Valentine, J.W. "'Hopeful monsters,' transposons, and the Metazoan radiation", Proc. Natl. Acad. Sci USA, 81:5482-5483, Sept 1984)
In other words, Miller has to explain why a random chromosomal fusion event which, in our experience ultimately results in offspring with genetic diseases, didn’t result in a genetic disease and was thus advantageous enough to get fixed into the entire population of our ancestors. Given the lack of empirical evidence that random chromosomal fusion events are not disadvantageous, perhaps the presence of a chromosomal fusion event is not good evidence for a Neo-Darwinian history for humans.
Miller may have found good empirical evidence for a chromosomal fusion event. But our experience with mammalian genetics tells us that such a chromosomal aberration could have created a non-viable mutant, or a normal individual who could not produce viable offspring. Thus, Neo-Darwinism has a hard time explaining why such a random fusion event was somehow advantageous.
If it were to turn out that the fusion of two chromosomes can only result in a viable individual if the fusion event takes place in a highly unlikely and highly specified manner, then we may actually be looking at a case for a non-Darwinian intelligent design event in the history of the human genus.