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Ear Development

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Ear development, like all other sensory systems, evolved from lesser structures in lesser animals. Research based on the work of Andrea Streit however places the burden of ear development solely on vertebrates (1H). Marine vertebrates evolved the first set of mechanoreceptors that could be classified as detecting sound since sound waves and pressure waves are nearly the same forms of energy. Once animals evolved to the stage where land traversing was possible the receptors were unable to accomplish the same tasks as they once did underwater, leading to the beginning of the development of the ear as we know it today.

The transition from a fluid environment to an air environment triggered the development / enhancement of the middle ear and the external collecting apparatus. In a marine environment, water can carry sound very far and efficiently. In air sound disperses and loses it's energy rapidly, requiring a large collecting apparatus, the external ear. Internally the middle ear was a response to convert air sound energy to an input that could be appropriately scaled and transferred to the fluid medium of the inner ear (2H).

Primitive land animals still retained the structures from their marine counterparts and as such did not have more modern structures specifically adapted for air based hearing; an enclosed middle ear cavity and tympanic membrane(1H). The bones of the middle ear were also not developed to the degree as is seen in later vertebrates, the main difference being the stapes. In humans it is one of 3 middle ear bones that transfer mechanical energy to the fluid of the inner ear. In the early land vertebrates it was integrated into the brain case and acted as a secondary support structure. See Figure 1H for a normal...

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...lia, a deficiency in Clotting Factor VII, a targeted drug can possibly alter that gene and institute partial function and creation of the deficient protein.

As discussed earlier in this paper, Human genes for hearing and Amphibian genes for hearing are remarkably similar and that similarity would only grow closer as one moves up the phylogenetic map as seen in Figure 3H and Figure 4H. The implications for this, at a human level, are that drug trials can be performed using many animals and they will still be relevant to human ear development. The most costly phase of any treatment trial is the clinical testing with humans due to the extreme length of time it requires as well as the man power to coordinate the trial. If this could be shortened through the use of viable animal models, by testing the relevant genes, then drug costs could conceivably drop dramatically.
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