Book Review: Your Inner Fish

This past week I finished Neil Shubin's book Your Inner Fish. It was a book that I was highly looking forward to reading, as I had heard a lot about it and thought it was a really good idea. The basic premise of the book is to look at our present day physiology and trace aspects of it back through the fossil record using all the tools of modern evolutionary science (from the fossils themselves to comparative DNA studies and developmental biology).

I think my expectations may have originally been overly high, considering that the book combined many things that I am a big fan of: comparative anatomy and physiology, paleontology, and evolution. What I failed to realise was that this was a fairly short, well-written popular science book, and therefore did not go nearly into the detail that I wanted. Despite Shubin's general skirting of complex details in lieu of making general points, the latter half of the book I found to be highly engaging, as there were a number of fascinating factual gems and I felt he started to feel more comfortable expanding the detail of his discourse, given the basic knowledge set he had introduced in the first half.

Thus, my biggest criticism of the book is that it could easily have been longer and more detailed. As it stands, it is a well-written and easily accessible overview of how our bodies are shaped by our evolutionary history. It is interesting, being about a subject that we are all aware of (the human body), with an interesting perspective that not a lot of people acknowledge or think about. I hope every school library gets at least a copy or two, and I think biology teachers would do well to point them out to their students.

Edit: I just wanted to point out that the first half of the book was good too! I simply found the second half engaged me more, but I realise that my initial wording of this post made it seem like that was the only good part of the book.

Quick Shot of Physiology

One thing that I remember always puzzling me as a kid was why my voice sounded different to me when played back on a recording device than when I spoke, but everyone else's voices sounded pretty much the same. While I am sure there are likely other factors to this auditory dichotomy, while studying for my physiology exam I realised I had one of the reasons in front of me. I also decided it was interesting enough to share.

In order to transfer sound waves from the air to the liquid inside the cochlea (the inner ear structure which actually contains the nerve cells of the auditory system), there is a rather interesting structure called the middle ear. The primary components of the middle ear are the tympanic membrane (commonly called the ear drum), which vibrates in response to sound, and the three smallest bones in the human body. These bones are collectively called the ossicles, and individually are (in order from outside to inside) the malleus, incus, and stapes. The ossicles form a chain linking the tympanic membrane to the cochlea, thereby transferring vibrations from the air to the liquid inside. Due to the physical limitations of the middle ear, not all frequencies of sound are transferred equally. There is an upper frequency limit bounded by the mass of the ossicles (they can only vibrate so fast) and a lower frequency limit bounded by the stiffness of the system (as an interesting aside, one of the main reasons smaller creatures like cats and mice can hear higher frequencies than humans is because they have smaller and lighter ossicles than we do).

In addition to the membrane and the bones, there is also a pair of muscles: the tensor tympani which attaches to the malleus, and the stapedius which attaches to the stapes. These muscles can contract and increase the stiffness of the system, thereby reducing overall sound transmission and protecting the inner ear from possible damage due to loud noises (this only works effectively, however, on either loud noises which are expected or long-term noise due to the time latency of the muscle reflex). Increasing the stiffness of the system, however, does not reduce the level of sound transmission equally across all frequencies. Since this protective muscular reflex engages in an individual person when he talks, a person consistently has different frequency transmission properties when he speaks versus listening to an auditory playback of his own voice.

Now it is time to get back to studying.