Communing with your inner fish

Continuing (and concluding) my series entitled “Books I Bought in Seattle,” I will now regale the reader with my impressions of Neil Shubin’s recent book, Your Inner Fish.

The book is an exploration of the history of human evolution, in the only place available to us: the bodies of other animals, extand and ancient. Shubin points out the one-to-one correspondence between the bones in our limbs, and the limbs of all other tetrapods, to those of the Devonian fish he helped discover, Tiktaalik. He describes how the general body plan of vertebrates was in place 550 million years ago in the Cambrian, and perhaps even in the Precambrian, as evidenced by the famous Ediacaran fossils. He similarly explores the evolution of vision, of hearing, of the sense of smell, and points out how all our wonderfully complex sense organs have analogues in far more (seemingly) humble creatures.

Shubin’s lively and playful writing captures the breathless excitement that surrounds each new scientific discovery, and I delighted in his accounts of the findings that shaped our knowledge of evolution. He succeeds in portraying scientists as ordinary people, whose job happens to be probing the underlying nature of the universe. I have to thank him also for his clear explanation of the gene Sonic hedgehog. The only complaint I would level against it is that I fear he sometimes dumbs down his accounts too much; there was more than one place in the book that I felt would benefit from the actual terminology, rather than a more general explanation by analogy. But this is a minor complaint, as evidenced by the fact that I did not provide an example.

The fundamental theme of the book is that, as remarkable as we are, we are an inextricable part of the tapestry of life, no more and no less remarkable than anything else that lives. Everything that makes us what we are is derived from something that ran or flew or swam upon the Earth before. Within each of us is an inner fish, and an inner ape, and an inner reptile, and an inner bacterium (trillions of these, actually); reading Shubin’s book is an excellent way to gain acquaintance with them. (Richard Dawkins’ The Ancestor’s Tale is another.)

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Most primitive tetrapod found

Today’s edition of Nature carries an article describing the most primitive tetrapod (four-legged creature) ever discovered. The creature, thought to have lived 365 million years ago, is ten years younger than the infamous Tiktaalik, but while Tiktaalik is thought to have more characteristics of fish than of tetrapods, the new discovery is thought to be a true tetrapod.

Some interesting notes:

The creature, named Ventastega curonica, is not the oldest tetrapod ever discovered, but it is the most primitive. This means that its features are more similar to fish (the ancestors of all land animals) than any other known tetrapod. This seems out of sequence with the usual trend in the fossil record, where more primitive animals are found in older rocks, and more complex creatures are found in newer ones. Because of this, the study’s lead author, Per Ahlberg, does not think that Ventastega is an ancestor of modern tetrapods, but rather an evolutionary branch that died out sometime in the past. That would have made it something of an evolutionary holdover in its time, somewhat like horseshoe crabs and egg-laying mammals today.

At the site in Latvia, no legs were found, but researchers were able to deduce that Ventastega had four legs through the shape of the pelvis and of other joints. Parts of the skull, shoulders and pelvis were all that was turned up.

Ventastega was probably three to four feet in length, and probably ate fish. It probably lived in shallow water, where its legs allowed it to move more efficiently than fins would have done. (Scientists say “probably” a lot.)

I love stories like this! Let’s hope paleontologists keep unearthing these key bits of the story of life.