I have argued in my book that the highly similar genomes of chimpanzees and humans (approximately 94% identity in DNA) imply ancestral relationship. However, people who support a creationist model commonly argue that humans and chimpanzees are genetically similar because they were created to be similar sorts of creatures, or made to a similar “pattern”. Of course (their argument runs), two creatures with such physical similarities will have similar genes. After all, two similar houses by the same architect will have similar plans.
I see two major flaws with such an argument:
Flaw 1: Looks are not predictive of genes.
Two creatures can look very similar and not be closely related. On the other hand closely related creatures, or people, do not always look very similar.
Imagine a paternity suit in which DNA tests have shown that the young man and the older man are son and father. The older man, however, claims that the young man is not his son. Using a similar argument to the creationist regarding chimps and humans, he suggests that it was inevitable that their genes would be similar because they look physically similar, generating a misleading result in the paternity test. In other words he is claiming that their similar looks mean they will share specific DNA sequences whether they are related by paternity or not.
A man like this has the facts back to front. In his case it is not the looks that determine the genes, giving rise to a false impression of relatedness. Rather, the shared specific DNA sequences show the relatedness between the young and old man, whether or not they look alike. A father and son are related precisely because of their shared DNA, passed from one to the other; the looks are secondary, and a son may or may not look like his father.
In fact, “looking alike” is not very clever at predicting genetic relationship because quite different genetic backgrounds can result in similar looks.
The rat and the Australian bandicoot look alike (see the illustration). But the bandicoot is a marsupial, more closely related to kangaroos and koalas, which it doesn’t resemble, than to the rat, which it does resemble. The rat is a placental mammal, more closely related to monkeys and elephants than to the bandicoot.
For an even more stunning comparison, check out these two websites comparing flying squirrels (placental mammals) with flying phalangers or sugar gliders (marsupials):
Many other examples of look-alikes that are not closely related exist among invertebrates, fish, and plants.
Why then is genetic comparison (as opposed to looking alike) so decisive in paternity suits and other genetic tests of relationship?
Flaw 2: Genes are not like an architect’s line drawings
Genes are highly specific codes that give rise to physical relatedness and inherited characteristics.
Imagine a photo-editing application you have bought and for which you have been sent the 30-character registration code. Something like:
Codes like this are not random, but nor do they follow a predictable pattern, so it is virtually impossible to guess them. You are not satisfied with that photo-editor so you buy another one from a different company. The registration code you are sent is:
The two codes share 28 characters in the same order. Is this what you would expect from a company that was operating entirely independently of the first? It suggests the second company is copying codes (and then modifying them slightly). Imagine two codes carrying on for 3,000 or 3 million characters with the same degree of identity as the codes above. Would two companies independently produce a photo-editing application with such similarity in programming code? Would the first company to produce such an application accept the second company’s argument that their programming codes are so similar only because both applications are for a similar purpose?
Now imagine the code carrying on for 3 billion (3,000,000,000) characters, with the same proportion – 2,800,000,000 (94%) – identical and the vast majority in the same order. That is the situation of the human and chimpanzee genomes. Highly specific codes with many shared sequences not found in any other creature. This is overwhelming evidence that copying has gone on. Is this what we imagine God has done by special creation? Or have the characters been copied by the normal process of DNA copying during reproduction?
DNA evidence of common ancestry is much more powerful than many other proofs we accept without question. If the older and younger man in the paternity suit are not related they should not uniquely share specific gene sequences. By the same argument, if we do not share ancestry with chimpanzees, as the creationist model states, we should not share so many specific genetic sequences. Uniquely shared genetic sequences and shared ancestry are in essence two ways of saying the same thing.
Unless, that is, God is considered to be an engineer resorting to copying DNA from another creature when creating man, because of limited imagination, resources or time (see page 257 in my book)
So when people say that our genes are like those of chimpanzees only because we look similar, they are arguing from effect to cause. If the creationist model is true, we should not be genetically related at all. The reality is that humans and chimpanzees look similar because they have so much shared family history, recorded in DNA. The genetic similarities are greater even than the similarities in looks.
The common ancestry of humans and chimpanzees is attested in far more detail than is required to prove paternity in a court of law.