Wesley Elsberry has a post up that he touts whenever something negative is posted about me on the internet, I wanted to examine some of Elsberry's claims. He writes:
I pointed out that the mammalian middle ear ossicular chain is an IC system providing an impedance-matching function, and that the impedance-matching goes away if you remove any of the parts. Nelson tried to deny that this qualified as IC, at least in part because the fossil record is clear that the system evolved.
Not surprisingly, that is completely false.
In the forum I had made it as clear as I possibly could that the theory that this transition had no possible intermediates was a purely creationist claim with not-so-much importance to the concept of irreducible complexity, due to the differences in concepts that exist for the evolution of molecular machines vs. morphological characters.
It's not that I agree with everything I have written on the internet (people change). However, I have no idea where Elsberry gets the notion that my argument that the middle ear bone system is not IC was due to the fossil record being clear that the system evolved. In fact, Behe was very clear in his book that IC systems, can evolve, through circuitous routes, something that Elsberry, to this day, is quite obviously ignorant of. So that was never the issue. Nonetheless, I was arguing in the thread Wesley links to, against PvM, who claimed quite explicitely that hearing itself was the function of the higher middle ear system. And PvM was ( and is) quite wrong.
My argument was very simple, the middle ear bone system, with respect to hearing, does not require every component and therefore it is not irreducibly complex. I've said this several times within the same post.
Elsberry , in the same post, kept harping on impedance matching:
My point was not that impedance-matching in the middle ear is
*necessary* to any amount of hearing, but rather that trying
to dismiss the impedance-matching function on the basis that
hearing itself is not completely eliminated is a digression.
However, it is not a "digression", as the same argument is employed against the irreducible complexity of the eubacterial flagellum, and has been for years. That the flagellum can lose various parts and still function as a type III secretory system has been used by anti-ID activists for over a decade, especially at the recent ID trial. And rightly so , not a digression in this context, because it is relevant when thinking about how it might have developed. Thus, I was employing the same reasoning for the middle ear system.
Given that the eardrum and the three middle ear bones are mechanically coupled in a serial fashion, impedance matching will be compromised if any part of the path is disrupted. However the hearing loss is not infinite due to interruption. This is because when sound reaches the oval and round windows it can still excite the cochlea leading to the perception of sound. With this direct acoustic route, the hearing sensitivity is compromised due to the impedance mismatch. In such a case a respective animal (no matter if lizard or mammal) would then be able to 'hear' if only vibrations in the ground or very deep sound.
It might be, however, that low frequencies, for example received by the lungs, would have alternate, non-tympanic pathways. This is certainly the case in frogs, where frequencies below 3-400 Hz apparently are received by 'extratympanic' pathways. This may be similar to bone-conduction, i.e. sound-induced vibrations of the skull. There are many species of 'earless' frogs that have secondarily lost their middle ear, and they have reduced sensitivity at higher frequencies compared to 'normal' frogs, but essentially unchanged sensitivity at lower frequencies.
In lizards, the situation seems to be the same. Since the ear is a pressure-gradient ear, the tympanic response at low frequencies is very small, that part of the low frequency sensitivity is extratympanic. However, at higher freqs hearing clearly depends on the eardrum and its impedance matching.
Regardless, one other point needs to be discussed, and this is with regards to fundamentals. Evolutionary changes around the ear are usually attributed to developmental 'regulatory' changes. In an evolutionary context, to understand how change in development leads to change in character states that can be selected for (ie, evolve) we need 1) to understand how development works, how developmental events actually yield character states, 2) be clear on how we identify a character state, and 3) formulate an ordering mechanism to describe the correlations of 1 and 2. Historically, developmental changes leading to morphological changes were thought to occur through changes in the timing or rates of a developmental event. More recently, workers in the field have considered changes in the relative positioning of a developmental event.
I would expect ear-bone evolution to involve developmental regulatory changes. Any change in the place or time of development of a structure is regulatory in nature. Changes in proteins are less likely to underlie such changes because most regulatory proteins are constrained due to their pleiotropic roles in the development of different structures. This is not to say, of course, that such changes are irrelevant, morphological evolution can also be affected by protein sequence changes. Thus, protein sequence change in a trans-regulatory molecule, (eg coding changes in a transcription factor) would affect downstream regulation of downstream genes. Gene duplication and divergence allows both regulatory changes in a copy, and changes in coding sequence to some modified activity of one of the copies, with the other maintaining its former activity. But certainly more important when it comes to molecular machines, which is the focus of Behe's first book.