Some alleged transitional forms are not ancestral to any modern organisms.
It is almost certainly true that none of the transitional forms scientists have discovered between higher taxa are directly ancestral to modern organisms. Because fossilization is such a rare event, and the extinction of entire lineages so pervasive in the history of life, paleontologists do not expect most of the fossils they find to be directly ancestral to modern organisms; moreover, even if someone were to happen upon a direct ancestor, it probably would be impossible to know it is a direct ancestor rather than part of a side branch. Because of these considerations, paleontologists generally presume that the fossils they find do represent side branches—the probability is just higher. However, this does not mean there are no fossils count as transitional.
The creationist argument appears to be that unless a fossil represents an organism directly ancestral to modern ones, it is irrelevant to the case for evolution. But this is not so. When paleontologists label a fossil "transitional," it is because the fossil (i) exhibits intermediate characteristics between ancestral organisms and modern ones, and (ii) is situated close enough in time to the hypothesized evolutionary transition to show us how it might have occurred. In Chris Nedin's eloquent way of putting it, a transitional form is an echo of the actual transition, not necessarily a creature that was itself involved in the transition. As one textbook on evolutionary biology makes clear, in the case of Archaeopteryx,
When we call Archaeopteryx a transitional fossil, we mean that it demonstrates that successful species existed that were intermediate in form between dinosaur and bird. (Freeman and Herron 2004:45)
Archaeopteryx is not likely the direct descendant of modern birds, but it does shows us that there is nothing at all problematic about a historical intermediate between reptiles and modern birds.
If the creationist account is correct, and there never have been evolutionary transitions between higher taxa, why do we find intermediate forms so close in the fossil record to where scientists expect to find them? One possibility is that God deliberately made creatures with intermediate characteristics, and also ensured that they would fossilize in a pattern consistent with evolutionary predictions rather than in any of the countless patterns that would outright refute evolution. Such actions, of course, would make God a liar and deceiver, and if God is a liar, then there is no reason creationists should expect Him not to have lied in the Bible, as well. This kind of argument, then, undercuts the entire foundation of creationism.
A second possibility invoked by more classic creationists (but, judging from their silence, apparently rejected as an embarrassment by contemporary intelligent design creationists) is hydrodynamic sorting during Noah's flood. Presumably, the world-destroying storm and flooding first killed virtually all of the life on Earth, then neatly sorted the remains into one of the relatively few patterns consistent with evolutionary predictions, and then rapidly turned all of the remains into fossils. Aside from the sheer physical implausibility of each step in this link, the question once again is raised as to why an honest god, who presumably wants people to believe in creation, would permit such a pattern to exist, knowing that it would mislead scientists who trust Him not to lie. A God so irresponsible with evidence either does not care what we believe, or cannot be trusted at all, once again undercutting a basic assumption upon which creationism rests.
Freeman S and Herron JC. 2004. Evolutionary Analysis: Third Edition. Upper Saddle River, NJ: Pearson.
Last updated: 24 Jan 2009
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