Probing the Mind of an Evolutionist

I ran across an interesting passage in a journal article that nicely illustrates how the bias of an evolutionist can blind them to the very thing they are studying. The article is titled “Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina,” written by Sereno et al., published in the journal PLoS ONE, volume 3, issue 9, on September 30, 2008.

To give some background information, one of the important differences between birds and other vertebrates is in the structure of their lungs. Other vertebrates have lungs like we do: bellow-type lungs where the air is drawn into the lungs and then pumped out, mimicking the action of a bellows. Birds, in contrast, have a series of air sacs around their lungs. These air sacs act as the bellows, drawing in and pumping out air. The lung itself does no pumping at all. Rather, it is only acts as a site for gas exchange, and the air sacs pump air through the lungs. The bird type of lung is called a flow-through lung, and it is the most efficient type of lung found in vertebrates.

If birds evolved from dinosaurs, which is the consensus among evolutionary paleontologists, then there must have been some point when a bellows-type lung evolved into a flow-through lung. The question they are now interested in is when. Did the flow-through lung begin evolving in early theropods (the group of dinosaurs birds are thought to be descended from) or did they appear latter, closer to the origin of birds?

Now look at what the previously cited article has to say. I am going to quote from it rather extensively.

"Two general models have been proposed for lung ventilation in nonavian [including theropod] dinosaurs. The first infers the presence of compliant lungs with crocodile-like diaphragmatic ventilation, based in part on stained areas in two theropod skeletons purported to represent a diaphragm separating thoracic and abdominal cavities. The stains and their interpretations have been contested, and the evidence for their arguments refuted by several authors. A second model infers avianlike flow-through lung ventilation with a rigid dorsally-attached lung and compliant air sacs. This hypothesis is based mainly on the morphology of the ribcage and on pneumatic sculpting in the axial column attributable to air sacs. Although more plausible, the second hypothesis actually consists of a collection of inferences about (1) pulmonary morphology and function and (2) the mechanics of aspiration respiration in nonavian dinosaurs." (italics for emphasis)

The crocodile-like diaphragmatic ventilation referred early on is a bellows-type lung. The stained areas in two theropod dinosaurs refer to a couple of small dinosaur skeletons that preserve traces of internal organs. The stains are thought by some to be traces of the liver. I might also add that these two theropod skeletons are the only theropod skeletons that have any significant traces of internal organs.

Here is where the interpretation bias comes shining through. Sereno et al. calls the second hypothesis (the idea that dinosaurs had flow-through lungs) “more plausible,” in spite of the fact that they immediately point out that that interpretation “consists of a collection of inferences”! Matter of fact, earlier in the article, they point out that the presence of pneumatic sculpting in the axial column gives no direct evidence for the existence of either a bellows-type or flow-through lung, and they also say that the morphology of the ribcage also gives no direct evidence for the existence of either bellows-type or flow-through type lungs. So they reject the hypothesis that is based on disputed interpretation of an actual piece of evidence (the stains in two small theropods) in favor of the hypothesis they acknowledge is based entirely on inference! Why then might they consider the flow-through hypothesis more plausible? Quoting from the article again:

"Tracking pneumatic patterns [of theropods] in the fossil record is complicated by the one-sided nature of outgroup comparison, which is restricted to birds among extant vertebrates, and the ambiguous meaning of the absence of a soft structure that only sometimes leaves an osteological imprint." (italics for emphasis)

An outgroup is a species that is known (or presumed) to share a common ancestor with the animals being studied. So what the authors are saying is that all they have are theropods’ closest relatives (birds) and ambiguous, absent, soft structures to determine what kind of lungs theropods have. As already shown, they acknowledge that there is no physical evidence that theropods had flow-through lungs, but there is disputed evidence that they had bellows-type lungs. Yet they go for the hypothesis that is based on no physical evidence because birds are supposed to be related to dinosaurs. This is a beautiful example of a presupposition affecting a person’s interpretation in spite of what evidence actually exists.