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18 June 2009

Homology Does Not Prove Descent

Once again, another in a long chain of "transitional fossils" that supposedly "proves" macroevolution. Fossil Solves Mystery of Dinosaur Finger Evolution,

Bird wings clearly share ancestry with dinosaur "hands" or forelimbs. A school kid can see it in the bones. But paleontologists have long struggled to explain the so-called digit dilemma.

Here's the problem: The most primitive dinosaurs in the famous theropod group (that later included Tyrannosaurus rex) had five "fingers." Later theropods had three, just like the birds that evolved from them. But which digits? The theropod and bird digits failed to match up if you number the digits from 1 to 5 starting with the thumb. Theropods looked like they had digits 1, 2 and 3, while birds have digits 2, 3 and 4.

That mismatch failed to support the widely accepted evolutionary link between dinosaurs and birds.

Now, newly described fossilized hands from a beaked, plant-eating dinosaur, called Limusaurus inextricabilis, reveal a transitional step in the evolution of modern wings from dino digits. The finding could resolve a debate over which fingers ultimately became embedded in the wing.


In case anyone is interested, you can see a photo of the dinosaur's hand.

First, the hand. Look, let's be honest here. The same kind of thinking that leads palaeontologists to reconstruct entire proto-human skeletons on the basis of a couple of bones from an extinct peccary is what leads them to assume the presence of a "vestigial first finger" in L. inextricabilis. The thinking in question is called "wishful thinking", and has led many a palaeontologist down the wrong path with all kinds of other supposed "transitional fossils."

More to the point, however, is the unquestioned assumption that homology implies phylogeny - in other words, because two structures look similar, then they must be related. In this type of case, biologists usually assume that if structures between two creatures look homologous, then this must mean that either one is descended from the other, or they are descended from a common ancestor. By that logic, then this,



and




must be evolutionarily related. After all, they're both tall, they look similar, they have hollowed out spaces in their interiors, creatures live in them, etc.

Ridiculous, of course, but then again, so is this current claim about dinosaur hands as they relate to birds' wings. We don't know which dinosaur fingers evolved into those found in birds' wings, but some of them must have, otherwise our theories won't work anymore. That's called "proving the evidence by the theory", which is the opposite of what science is supposed to be about. The assumption of phylogeny from homology in this case, as with other "transition fossils" (like the much ballyhoed Tiktaalik) is entirely gratuitous. There's no reason for it, other than to make the data fit an a priori assumption about phylogeny. And quite frankly, the claim of "homology" (i.e. that the bones in birds' wings and dinosaur hands are structurally similar) in this case is....imaginative....at best.

Homology does not prove the transitional nature of this fossil, despite the claims of the article. From a strictly empirical viewpoint, homology - at best - can suggest that similar structures may be present in different species to perform similar functions. Homology does NOT disprove special creation, either. God is certainly free to have used similar designs across different species, if He intended. That's not a scientific argument, you say? True. But neither is the a priori assumption that evolution must have taken place, so it's okay to fit the data to the theory, instead of vice versa.

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