Fish Gill Evolves toward Tetrapod Ear?
“This is another nail in the coffin of the creationist view, in my opinion,” said the curator of Chicago’s Field Museum about a paper published in Nature,1 reported the Washington Post yesterday (see MSNBC News). Brazeau and Ahlberg of Uppsala University in Sweden examined the skull of Panderichthys, a Devonian lobe-finned fish, and found what they are calling a transitional form between gills and ears. They found a spiracle (respiratory channel) they are claiming is intermediate between the gills of the Devonian fish Eusthenopteron and the middle ear bones of the purported earliest tetrapods like Ichthyostega and Acanthostega (08/09/2003, 07/03/2002, 08/03/2004).
The origin of the middle ear in tetrapods has “remained elusive,” the researchers said, “with little indication of how this transformation took place.” After examining the skull of Panderichthys, they claim that this spiracular region was “radically transformed” from earlier lobe-finned fishes, and “represents the earliest stages in the origin of the tetrapod middle ear architecture.” Though the spiracle resembles that of tetrapods, it was still used for respiration in Panderichthys, they believe, but later developed into a larger middle ear channel in which a bone called the hyomandibula developed into a stapes (a middle ear bone). This, in turn, was co-opted for use as a sound-transmitting device. From there, mammalian ears developed.
The news media are taking notice of this transitional form to hammer creationists. “Question: What do you do with half an ear? Answer: You breathe through it,” wrote David Brown for the Washington Post. This answers the creationist claim that organs like the ear are “too complicated to have evolved step by step” and therefore “had to have been created in their final form.” If the structure had an intermediate function, it could have had survival value, in other words.
Their conclusion is controversial, as it amounts to a radical reinterpretation of how the ear developed in land-based animals. If it withstands scientific scrutiny, the fossil will be a rare example of an organ glimpsed partway along its evolutionary path, at a point when its function was very different from that of its final form. (Emphasis added in all quotes.)
Both the Washington Post and LiveScience indicated that not everyone is ready to jump on the bandwagon, however. Bjorn Carey in LiveScience pointed out that this differs from previous beliefs that ear evolution began after the transition to land. Also, since no soft tissues are preserved in either Panderichthys or the early tetrapods, no one knows how these spiracles were actually used. David Brown ended with a quote from Michael LaBarbera (U of Chicago), an expert on the functional anatomy of the extinct animal, who is not convinced the structure even is a spiracle. He criticized the theory of Brazeau and Ahlberg as being “based on the interpretation of a structure that would be completely novel and unprecedented in this lineage.”
1Brazeau and Ahlberg, “Tetrapod-like middle ear architecture in a Devonian fish,” Nature 439, 318-321 (19 January 2006) | doi:10.1038/nature04196.
Let us pause for a moment to think like a consistent evolutionist. This is very hard to do and is rarely accomplished. It requires purging our minds of certain persistent myths and misconceptions promulgated by textbooks and TV animators. First, we must disavow orthogenesis. The concept of “straight-line evolution” is out; we cannot arrange Eusthenopteron, Panderichthys and Acanthostega on a straight line and imagine one form evolving in a direct fashion to the other. No – we must picture evolution branching out in a tree or bush-like pattern, and, therefore, place all these fossils at different points on different branches. Next, we must disavow Lamarckianism. There is no inheritance of acquired characteristics. If an early Panderichthys acquired a spiracle by accident or striving, such a structure would not be inherited unless the mutation affected the germ line. Third, we must disavow teleology. None of these creatures were “trying” to evolve an ear, or even a spiracle. There was no purpose or goal of achieving a fully functioning tetrapod ear. Evolution cannot see into the future. Natural selection acts only on present survival requirements. Finally, we must disavow vitalism. None of these creatures had any kind of world-soul or vital energy driving them upward by some inexorable path toward higher degrees of complexity and organization. The fitness landscape is not a mountain, but a chaos of undulating, dynamic hills and valleys. Ready? Good, let us proceed.
Now, we consistent evolutionists are ready to give an honest look at the challenges of those pesky creationists. They say that it is not just the bones of fossils, but the missing soft parts, that are key to understanding the impossibility of getting irreducibly-complex organs via natural selection. The mammalian ear, they say, has a cochlea, an organ of Corti with molecular springs and motors, a tympanic membrane, some finely-tuned bones that act like levers, and a complex brain to interpret the electrical signals transduced mechanically from air or liquid to nerve impulses. They say that there should not be one questionable transition, but thousands of them. They also say that these alleged transitions must have complete functionality at each stage, such that they outcompete those lacking the function to the point of remaining the only survivors in a vast battlefield of death (the cost of selection). They point to “living fossils” like Coelacanth that were long thought to represent transitional forms, only to be found alive and well in the present day (and not using their lobed fins for anything resembling walking). They embarrass us with the shortness of time in our scheme for coming up with major new body plans and organs, and they cast doubt on the dating and timing of the few existing fossils. They tease us by saying that these branches would have had to be “evolutionary dead ends” that went extinct and therefore did not go on to develop functional ears. And they pester us with reminders that new function requires new genetic information. They criticize this paper as representing little more than a just-so story unless a detailed series of steps can be elucidated to show how new information for a spiracle or ear was embedded into the genes and then translated into proteins and developmental programs. In short, they are not quivering at this announcement, and have delivered us all these counter challenges. So now, let us consistent evolutionists, having cleansed our minds of misconceptions, rise to the occasion and answer them. Who will be first? Isn’t there someone? Isn’t there anyone? Goliath, how about you? Pretty please? No fair hiding in that coffin we built for the creationists.
The ancient biosphere was more diverse and ecologically rich than our modern world. Many extinct species are found in the record. Undoubtedly these can be arranged and rearranged into all kinds of imaginary ancestral relationships. Evolutionists have a bad habit of arranging only the similarities that fit their preconceived imaginary trees into homologous groupings, and calling other similarities analogous. Why shouldn’t a school kid look at a proboscis monkey, a tapir and an elephant and use similar reasoning to think this is a transition from nose to trunk? Or a jellyfish to sea slug to a jelly sandwich? Maybe mudskippers and walking catfish are evolving into lizards or salamanders, or butterflies into birds, or penguins and seals into whales. Sea stars have five fingers like a human hand. Octopi have eight tentacles and spiders have eight legs. Similarities are everywhere; why get worked up about a select few? Could it be because they reinforce a favorite story?
For more on problems with the fish-to-tetrapod transition in evolutionary theory, see the review of the evidence by Paul Garner from the Creation Technical Journal.