The issue I focused on is common descent: according to evolutionary biology, all life is related in a huge family tree, ultimately leading back, over billions of years, to a common ancestor. According to young earth creationism (accepted by Mr. Mackay), each kind of creature had separate origins at the hands of a creator less than ten thousand years ago.

So there are two accounts on the table. Over 99% of biologists believe that the evidence, as collected in billions of pages of biological journals, overwhelmingly demonstrates the fact of common descent. (My opening argument from earlier in this blog summarizes just one example of the sort of thing that has convinced the biologists.) Young earth creationists deny that the evidence points this way. One of the two must be deluded about where the evidence actually points – who is it? Both sides claim that the other side is deluded because of an adherence to some unquestioned dogma. I set out to test both proposals.

Young earth creationists’ proposal: Biologists are deluded by their adherence to atheism. But this can’t be right, because 40% of biologists believe in God.
Biologists’ proposal: Young earth creationists are deluded by their adherence to a literal or inerrantist interpretation of Genesis. This holds up, because all of the small number of biologists who accept young earth creationism are conservative Christians (or conservative religionists of some other variety). Also, there are no biologists who accept some non-religious version of separate origins.

So I concluded that it is the young earth creationists who are being misled by dogma: the dogma that Genesis is inerrant or literally true. Therefore the biologists, who are not being misled as the creationists claim they are, must be right that the evidence points massively towards common descent.

I then considered the following response a young earth creationist might make: Even if the biological evidence points massively towards common descent, this is outweighed by the evidence to be found in Genesis. That evidence is simply more powerful than all the biological evidence; the Bible is inerrant.

I rejected this move on two grounds: 1) It is dogmatic; no piece of evidence can be assumed to have such power; and 2) There are independent reasons to reject Biblical inerrancy or literal truth. My main example was the Biblical claim that homosexuality is an abomination, and gays & lesbians deserve death. (This is a claim that Mr. Mackay accepts on the basis of his stated view that the Bible is inerrant.) This claim is obviously false, and so demonstrates that the Bible is not inerrant.

Therefore I concluded that biologists are right to insist that the evidence points massively towards common descent. This does not strictly entail that common descent is true; but it certainly demonstrates that it would be irrational to believe otherwise. Young earth creationists should admit this.

In passing, I pointed out that Christians can – and most do – accept both evolution and the Bible. All that need be rejected is a literal interpretation of a few chapters in Genesis. That tiny concession does absolutely nothing to undermine the value of Christianity.

Addendum: There has been some controversy over my use of the homosexuality example; some people are under the misapprehension that I raised this point only to discredit Mr. Mackay, and that it was not relevant to the issue. While I agree that it amply discredits Mr. Mackay, I used it simply because it was essential to my argument as an independent reason to reject Biblical inerrancy. I also mentioned some other examples, but I focused on this one because I knew for certain that Mr. Mackay accepted it. Another good example is “When a man strikes his male or female slave with a rod so hard that the slave dies under his hand, he shall be punished. If, however, the slave survives for a day or two, he is not to be punished, since the slave is his own property.” [Exodus 21:20-21 NAB]. But I do not know what Mr. Mackay thinks of that particular outrageous claim.