Tuesday, November 27, 2007

Human Chromosome #2

Ken Miller and Darwinists in general are very fond of using human chromosome #2 as a testament to their faith in common descent.

Evolutionists like to pose these points as their evidence:

All great apes apart from man have 24 pairs of chromosomes. There is therefore a hypothesis that the common ancestor of all great apes had 24 pairs of chromosomes and that the fusion of two of the ancestor's chromosomes created chromosome 2 in humans. The evidence for this hypothesis is very strong.

Evidence for fusing of two ancestral chromosomes to create human chromosome 2 and where there has been no fusion in other Great Apes is:

1) The analogous chromosomes (2p and 2q) in the non-human great apes can be shown, when laid end to end, to create an identical banding structure to the human chromosome 2. (1)

2) The remains of the sequence that the chromosome has on its ends (the telomere) is found in the middle of human chromosome 2 where the ancestral chromosomes fused. (2)

3) the detail of this region (pre-telomeric sequence, telomeric sequence, reversed telomeric sequence, pre-telomeric sequence) is exactly what we would expect from a fusion. (3)

4) this telomeric region is exactly where one would expect to find it if a fusion had occurred in the middle of human chromosome 2.

5) the centromere of human chromosome 2 lines up with the chimp chromosome 2p chromosomal centromere.

6) At the place where we would expect it on the human chromosome we find the remnants of the chimp 2q centromere (4).

Not only is this strong evidence for a fusion event, but it is also strong evidence for common ancestry; in fact, it is hard to explain by any other mechanism.

Of course it's hard to explain in other terms if you've been slipped the Darwinian Blue Pill, but let's go ahead and consider the following...

The problem with the conclusion, and with much of the discussion, is that it mingles the evidence with the explanation--so the conclusion, as stated, assumes that there was a common ancestor between apes and humans, which makes it difficult to use it as evidence for a common ancestor. To untangle this, let's rewrite the conclusion so that it no longer makes this assumption:

The evidence that human chromosome 2 is the fusion of two chromosomes is overwhelming. The two chromosomes it appears to derive from are directly analgous to chromosomes that are found in apes.

However, once you make this change, an explanation that agrees with creationist accounts of human ancestry just falls out. It would go something like this:

Humans were created in a separate creative event from the other primates, but with 24 chromosome pairs just like them. At some point early in human history, fusion of the chromosomes occurred to give us the 23 pairs we have now. All living humans are descended from those in which the fusion occurred.

The point is simply this: the evidence points to the fusion of human chromosomes, but gives no indication when this happened, except that it must have occurred to a creature that was the ancestor of all living humans. Since none of the apes share this fused chromosome, there is no reason at all to date this fusion any further back than warranted, so it becomes unnecessary to even posit the existence of a common ancestor between apes and humans based on this evidence alone.

What is interesting is this: at first glance, looking from an evolutionary perspective, this seems to have dealt a death blow to creationist accounts of human origins. (The main problem for the creationist is why God would have chosen to create humans with chromosomes that have useless bits in them i.e. the telomene sequences in the middle, and in a way that mimics fusion of 2 chromosomes).

But actually, the evolutionary interpretation has overstepped the mark -- it doesn't demonstrate common ancestry, it assumes it. All the way through it talks about the chromosomes of a common ancester etc. But by putting the evidence into the evolutionary framework ahead of time it has confused what the evidence actually points to. The evidence does indicate (assuming that the God-created-it-to-look-like-fusion explanation is invalid) that human chromosomes were once more similar to those of apes than they are currently, but that is all.

The article also states:

Not only is this strong evidence for a fusion event, but it is also strong evidence for common ancestry; in fact, it is hard to explain by any other mechanism.

The main basis for saying this appears to be the statement: "At the place where we would expect it on the human chromosome we find the remnants of the chimp 2q centromere". But of course, as the author explains later, we don't actually find the chimp 2q centromere -- there is no label on it saying "I'm a chimp 2q centromere". What we find is the remnants of centromere that is in the same place, relative to certain sequences, as the 2q centromere is in chimps. All this shows is that the ancestor chromosomes (i.e. before the fusion event) of current human chromosomes were closely analagous to chromosomes of apes, including chimps.

So the author claims we can rule out other accounts of human origins, but is unjustified in doing so. The reason for this logical mistake is that he/she has intertwined the evidence and the evolutionary explanation so tightly, and seen that they fit so well, that the author cannot imagine another explanation would fit. In reality, the evidence fits a creationist explanation equally well--there is nothing contrived or tricky about what I have presented, and if evolutionary theory did not exist, there is nothing in this evidence that would make creationists think of common descent. The idea that humans originally had a complete set of chromosomes that correspond to ape chromosomes, rather than only 23 out of 24, does not shake creationist ideas one little bit. We already knew there was a vast amount of similarity between humans and primates both in terms of physical characteristics and genetic material and structure. It is a mistake of the evolutionary mindset to assume that observing similarities necessarily brings you to the conclusion of common descent. Taxonomy based on physical characteristics was already a very well established science when the idea of common descent came on the scene, and people from both the intelligent design and the creationists camps have no problem in understanding physical and genetic similarities that are not rooted in common descent -- that is, it is easy to think of perfectly adequate reasons why a designer (either an unknown intelligence in the case of ID, or God in the case of creationism) might have reused designs.

A lesson for both sides to take away is the importance of detaching yourself from your current position in order to see where the evidence actually points. It is easy to imagine that because evidence fits with your position, and fits very well, it therefore not only confirms your position but disconfirms the rival theories.

Just something to think about...

EDIT: Here is another link on chromosome fusion.

When an educator brings up this particular chromosome fusion event, be sure to consider and share the following questions:

1) HOW did this fusion event happen?
2) At what stage in reproduction?
3) Do you have one fusion event in one person?
4) If so, HOW is that reproduced into the population?
5) Can this “human” with the fused chromosome reproduce with the primate with two separate chromosomes?
6) If not, then does this require two chromosome fusion events?