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Letter to the editor

'Your Inner Fish' reveals the finned fossil in all humans

By Shary Lyssy Marshall, Special to the Times
Published March 9, 2008

Your Inner Fish: A Journey Into the 3.5 Billion-Year History of the Human Body
By Neil Shubin
Pantheon Books, 230 pages, $24 

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Which came first in human history - teeth or skulls?

In Your Inner Fish: A Journey Into the 3.5 Billion-Year History of the Human Body, paleontologist and anatomy professor Neil Shubin brings us back to the swamp where, evolutionarily speaking, it all went down.

"All animals are the same but different," he writes. "Like a cake recipe passed down from generation to generation - with enhancements to the cake in each - the recipe that builds our bodies has been passed down, and modified, for eons. We may not look much like sea anemones and jellyfish, but the recipe that builds us is a more intricate version of the one that builds them."

Among the surprises Shubin's book offers for nonscientists are explanations of common ailments. Hiccups, for example, which we share with other mammals such as cats and dogs, seem to be controlled by a small patch of tissue in the brain stem. The pattern generator responsible for hiccups is identical to the one in tadpoles. A bother for us, this process allows tadpoles to use both gills and lungs to breathe.

Speaking by phone from his office at the University of Chicago recently, Shubin said that as he wrote, he imagined his father, who is well educated but not a scientist, sitting with him. "I had him sort of at the end of the table. I wanted to explain this to him."

Shubin, a rare beast himself, moves easily between the worlds of scientist and regular Joe. He brings readers from paleontology digs to the laboratory, exploring why humans are prone to sleep apnea and hemorrhoids, and probing the cellular relationship between teeth and skin.

"Typical summers of my adult life are spent in snow and sleet, cracking rocks on cliffs well north of the Arctic Circle," he writes in Chapter 1. "Most of the time I freeze, get blisters, and find absolutely nothing. But if I have any luck, I find ancient fish bones. That may not sound like buried treasure to most people, but to me it is more valuable than gold."

Shubin's gold made headlines in spring 2006 with the discovery of a 375-million-year-old fish fossil named Tiktaalik. Tiktaalik, which means freshwater fish in Inuit, filled a link previously missing in the fossil record, connecting water and land animals.

"Tiktaalik's message is so simple, even preschoolers can see it," Shubin writes, describing how he took a cast of Tiktaalik to his son's preschool classroom. Upon studying it, they could see it had a flat head and eyes on top like an alligator, but scales and fins like a fish. "Maybe it's both," one child suggested.

Shubin recalls his development as a paleontologist, including some of his earliest experiences as a young graduate student walking the Arizona desert.

Unlike the rest of the team, he couldn't find anything. At the end of each day, "my empty bag (was) a sad reminder of how much I had to learn," he writes.

After weeks of tagging along with a more experienced and very patient mentor, "All of a sudden, the desert floor exploded with bone; where once I had seen only rock, now I was seeing little bits and pieces of fossil everywhere."

Readers might be surprised to learn that teeth appear in the fossil record before bones. Shubin tells the story of how conodonts, the plentiful fossil from ancient oceans, puzzled 19th century scientists who debated whether they were animal, vegetable or mineral.

One day a paleontologist discovered what looked like a lamprey fossil. Inside the mouth of this primitive, jawless fish were rows of conodonts - teeth! Those teeth, the earliest on record, had been observed 150 years before anyone realized what they were. It turns out that multiple rows of teeth formed the building blocks of skulls, pushing back - eon upon eon - to cover the brain.

Those first bony-head skeletons, which belonged to a group of fish called ostracoderms, looked "like hamburgers with fleshy tails," writes Shubin. The fossilized skulls of these fish are shiny, like teeth or fish scales. When this skull is studied under a microscope, "the whole shield is made up of thousands of small teeth fused together."

Shubin's story is about the odyssey of how we grew into bodies - teeth, skull, brains and bones - that began as fish.

He hopes it won't be seen as kindling for the debate over evolution vs. creationism.

"I didn't want to write an angry book," Shubin said. "I wanted to write a happy book. A book about the beauty of science."

Shary Lyssy Marshall is a former elementary school teacher and administrator. She lives and writes in the Tampa Bay area.

[Last modified March 6, 2008, 12:02:34]