[Continued from part #1]
The specimen they studied was unearthed in Latvia in the 1970s and resides in a museum in Riga. Previous studies of the skull were done before all the rock encasing it was removed. Looking at it in its less-obstructed form, Brazeau said they noticed two things. First, a bony channel leading to a hole in the skull called the spiracle was much wider and straighter than in more primitive fish. Second, a bone called the hyomandibula was much shorter and stubbier. The spiracle is a modified gill slit. Sharks and rays have them on the top of their skulls behind their eyes. They use it for respiration while feeding on the bottom to avoid drawing grit into their gills. Uppsala researchers believe Panderichthys did the same thing. "This fish probably lived on the bottom, probably in shallow water. It was almost a crocodile-like fish," Brazeau said. "It may have inhaled and exhaled through this passageway. It may, in fact, have breathed air through it occasionally." Paleontologists have known for a long time that the hyomandibula -- which helps suspend the jaw in fish -- evolved into the stapes, or "stirrup bone," that helps transmit sound vibrations in the middle ear in reptiles, birds and mammals. [I have no problem with this, except I would not say it "evolved into the stapes" but that God progressively created the mammalian ear from the fish through the reptile jaw.]
When Brazeau and Ahlberg measured this bone in Panderichthys, they discovered it was much shorter than in earlier fish. It also was not directly connected to the jaw joint. It appeared to be in the middle of moving to a different part of the skull where it would become an ear bone -- a migration that would take tens of millions of years to complete. "This stage sets up the skull and makes it possible for this region to be modified into a middle ear. The interesting thing is that at this point it appears to have nothing to do with hearing," Brazeau said. [Which shows that it was not naturally selected for hearing. In discussing the reptilian jaw - ear transition, Gould asks "why should such a transition occur ... since the single-boned stapedial ear seems to function ...every bit as well as the three-boned mammalian ear":
"Embryology and paleontology provide adequate documentation of the `how,' but we would also like more insight into the `why.' In particular, why should such a transition occur-especially since the single-boned stapedial ear seems to function quite adequately (and, at least in some birds, every bit as well as the three-boned mammalian ear)?" (Gould S.J., "An Earful of Jaw", "Eight Little Piggies: Reflections in Natural History," Jonathan Cape: London UK, 1993, p.106. My emphasis)
And, as Hitching points out, if the "why" was for stereophonic hearing, "The stereophonic effect can only work when the inner and outer ears have been fully displaced":
"Darwin wrote: 'Natural selection tends only to make each organic being as perfect as, or slightly more perfect than, the other inhabitants of the same country with which it has to struggle for existence.' [Darwin C.R., "The Origin of Species," , First Edition, Penguin: London, 1985, reprint, p.229] The trouble with the mammal ear is that, in terms of natural selection, it has nothing of enough significance to justify its enormously complex system having emerged by natural selection. Amphibians, reptiles, and birds, all of which have only one earbone, can perceive pitch and volume at least as well as mammals, and in some cases better. The sole possible advantage is that mammals can hear to some extent stereophonically, while it is thought creatures with single earbones cannot do this quite so well. ... In the case of mammals, stereophony happens because our brains receive signals from both the outer and the inner ear, and the fractional delay in the sound impulses may enable us to estimate how far away a sound is coming from. In survival value, this might confer a minimal advantage in, for instance, spotting prey or escaping predators. But even if this ability were proved (for doubts still remain), it is hard to see how the transitional forms leading up to it could have made the ear, in Darwin's words 'slightly more perfect'. The stereophonic effect can only work when the inner and outer ears have been fully displaced." (Hitching F., "The Neck of the Giraffe: Or Where Darwin Went Wrong," Pan: London, 1982, p.93. My emphasis)
I have seen somewhere (but can't find the quote at present) that the reptilian jawbones becoming earbones enabled the mammalian (and ultimately the human) brain to expand, so my mediate creation theory has an answer to Gould's "why" that his naturalistic evolutionary `blind watchmaker' theory cannot give: that a far-sighted Intelligent Designer initiated the changes to as part of the mammalian and human `construction projects.']
Only when the fish's descendants became land-based and breathed through their mouths and nostrils was this passageway "free" to evolve into a sensory organ, he said. There are serious doubters of this interpretation of the fossil, however. Michael LaBarbera, a professor of organismal biology and anatomy at the University of Chicago, is an expert in the functional anatomy of extinct animal. He isn't certain that the key structure that Brazeau and Ahlberg say is a spiracle is, in fact, one. Their theory is "based on the interpretation of a structure that would be completely novel and unprecedented in this lineage," he said. And he's not convinced. ... [I certainly would have no problem with "a structure that would be completely novel and unprecedented in this lineage," but I await the experts thrashing this out.
Here is another quote on the ear by an atheist/agnostic engineer that had a big effect on me when I saw part of it posted on the Calvin Reflector in 1995:
"With all this, of course, went improvements in the brain, most notably the power to compare the times at which signals from one source reach each ear, thus providing a method of estimating the direction in which the source lies. Thus, in the course of evolution, there were six major developments, two of which occurred in the fishes, two in the amphibia and two in mammals. Such, at least, is the account given by people like Willem van Bergeijk, of Bell Telephone Laboratories who is the acknowledged authority. But the eminent morphologist J. W. Torrey is not convinced. 'The evolutionary origin of the inner ear is entirely unknown,' he insists. In contrast with the case of the eye, where undifferentiated cells were specialised into the required forms, here existing structures have been profoundly modified and even shifted to another position in a progressive series of changes which certainly look more like the refinement of a plan than the result of a series of happy accidents. But the insoluble problem is how and why did a balance organ become an organ of hearing? As van Bergeijk pointedly asks: 'What prompts the fish to begin developing a sensory apparatus that will respond to a stimulus about the very existence of which the fish knows nothing?' Van Bergeijk believes that the original balance organ would never have evolved mechanisms for hearing but for the emergence of the swim bladder. The original purpose of this organ is to enable the fish to adjust its density to the density of the ambient water and so control the depth at which it swims. Since the bladder is sensitive to changes in external pressure, it vibrates in harmony with pressure changes in the water. In time these vibrations came to excite the ear. Hearing as distinct from the mere detection of pressure waves, was born. After describing the last part of this process, the adaptation of the bones linking the jaw to the skull into a chain of ossicles linking the eardrum to the inner ear, Ernst Mayr sweepingly remarks: 'Not all the steps in this process are yet entirely apparent, but I think little doubt is left as to the principle involved.' If by 'principle' one means merely progressive remodelling, the statement is a truism. But if 'principle' means that chance selection brought about these elaborate changes, then there must be very great doubt indeed. Like de Beer, Mayr does not seem to appreciate the elementary point that demonstrating the occurrence of a sequence of events does not explain why they happened. But what kind of mutations could bring about the major changes I have described? Could cause a tube to roll up into a helix? Could cause other tubes to form semi-circular canals accurately set at right angles to each other. Could grade sensory hairs according to length? Could cause the convenient deposit of a crystal in the one place it will register gravity? Even more amazingly, some fishes do not trouble to secrete a crystal but incorporate a bit of sand or stone. What kind of mutation could achieve this - when and only when a natural crystal is not formed? The purpose is fulfilled, the means are unimportant. It just doesn't make sense." (Taylor G.R., "The Great Evolution Mystery," Abacus: London, 1983, pp.105-106. My emphasis)
I have added the above quote to my "Problems of Evolution" book outline, section PE 13.8.1. "Mammals ? Reptile jawbone-mammal earbone transition." Again, I agree that it happened-my disagreement with evolution is how it happened.]
AN>Hoping to hear from you,
Thanks again for your question. I am not sure of your position on the creation-evolution spectrum (although your pseudonym suggests you are opposed to atheism), but I hope this has been of helpful, although I am sure you did not expect such a lengthy reply. However, the reply is primarily intended for my blog. I have a long-standing policy not to get involved in private discussions on creation/evolution/design issues.
Stephen E. Jones, BSc (Biol).
"Problems of Evolution"
Post a Comment