The Language of God, Chapter 5
By B.J. Marshall
In the last post, we saw Collins give a foothold to Creationists who want to deny macroevolution. Even granted that he should have never allowed this foothold in the first place, he makes a valiant effort to tear the false micro-v-macro wall down by comparing our genome to those of other animals. It is here that Collins asserts that “[t]he study of genomes leads inexorably to the conclusion that we humans share a common ancestor with other living things” (p.134). Aside from the genetic similarities discussed in the previous post, Collins presents three additional lines of evidence that help lead us to his inexorable conclusion: the order of DNA sequences, ancient repetitive elements (AREs), and pseudogenes.
I think Collins doesn’t spend much time on the first line of evidence, the order of DNA sequences, because it’s pretty easy to follow. The argument is something like this: If you find human genes A, B, and C in that order, you are also likely to find A, B, and C (same order) in other animals. The spacing might differ, but it’s there. (AREs fill in most of the gaps between these protein-coding genes, so that’ll come into play shortly.) His example to demonstrate this is a comparison between a human and a mouse genome. Particularly, virtually all the genes on human chromosome 17 are found on mouse chromosome 11. Collins here takes a stab at a potential objection. While one might argue that the order of genes is critical in order to function properly – therefore hinting at a Designer – there is no evidence supporting the claim that this would have to occur over such large chromosomal differences.
Now we get to these AREs, called “jumping genes” or transposons, that fill most of the “junk DNA” portion of genomes. They comprise about 45% of our genome and, when one aligns these AREs in human and mouse genomes, they occur in the same order. So, not only do the protein-coding portions line up, but so do these AREs. Collins points out that the process of transposition often damages the jumping gene, and that’s what makes them “junk.” And these don’t bode well for the Creationist; “[u]nless one is willing to take the position that God has placed these decapitated AREs in these precise positions to confuse and mislead us, the conclusion of a common ancestor for humans and mice is virtually inescapable” (p.136-7).
Bringing AREs closer to humans, Collins moves to comparing us with chimpanzees. Humans have 23 pairs of chromosomes; chimps have 24. The difference appears to be where two proto-chimp chromosomes fused together to create human chromosome 2. (I say proto-chimp as means of refering to the common ancestor that led to chimps and humans. It’s my attempt to avoid that horrendous claim “we evolved from monkeys.”) What’s more, Collins argues, is that scientists found this fusion exactly where they predicted it would be! The fusion would be “very difficult to understand … without postulating a common ancestor” (p.138).
Finally, Collins comes to pseudogenes, which are genes that have almost the same properties of a functional DNA instruction packet but have some glitches that muddle things up. Three examples include capsase-12; MYH16, the gene for a jaw muscle protein; and FOXP2, involved in the development of language. Capsase-12 is inactive in humans but active in chimps. This gene works just fine in nearly all mammals except us. So, Collins asks, why would God have gone to the trouble of inserting such a nonfunctional gene in this precise location?” (p.139). MYH16 plays a significant role in the development and strength of jaw muscles in other primates. Collins states that inactivating this gene freed our skulls from having to anchor larger jaws and enabled us to expand our skulls outward to accommodate larger brains. Finally, FOXP2 enables language. Collins talks about uncovering this gene on chromosome 7 via a single family in England where members for three generations had severe difficulty in speaking. They found that a simple one-letter misspelling was occuring. This gene has been remarkably stable in nearly all mammals, and two significant changes have occurred in the coding region of this gene to finally (as in, as recently as 100,000 years ago) imbue humans with the capacity for language.
At this point, Collins mentions, “godless materialists might be cheering. If humans evolved strictly by mutation and natural selection, who needs God to explain us? To this, I reply: I do” (p.140). Stay tuned for Collins’ explanation of why he thinks that; the next post will get to the heart of Theistic Evolution.
Other posts in this series: