According to Darwin, all living things are related in the strict sense of a having a shared family tree. But there’s a more general and obvious sense in which living things are related. It’s the sense of having noteworthy similarities—the sense in which snowboarding, skateboarding, and wakeboarding are related (or iPhones and iPads, or Jupiter and Saturn). So, how do we know whether living things are really all related in the strict sense?
Until recently, the answer was that a real family tree should generate a fully consistent pattern of similarities. For example, we are told that chimps and humans came from the same ancestral stock (call it CH stock) and that gorillas, chimps and humans all came from an earlier ancestral stock (GCH stock). If so, then the human and chimp genomes should consistently be more similar to each other than either is to the gorilla genome, since the human and chimp histories were one and the same thing more recently than the human and gorilla (or chimp and gorilla) histories were.
Well, the recent publication of the gorilla genome sequence shows that the expected pattern just isn’t there. Instead of a nested hierarchy of similarities, we see something more like a mosaic. According to a recent report , “In 30% of the genome, gorilla is closer to human or chimpanzee than the latter are to each other…”
That’s sufficiently difficult to square with Darwin’s tree that it ought to bring the whole theory into question. And in an ideal world where Darwinism is examined the way scientific theories ought to be examined, I think it would. But in the real world things aren’t always so simple.