Weekly reading: Your Inner Fish

16 Mar

“Carl Sagan once famously said that looking at the stars is like looking back in time.  The stars’ light began the journey to our eyes eons ago, long before our world was formed.  I like to think that looking at humans is much like peering at the stars.  If you know how to look, our body becomes a time capsule that, when opened, tells of critical moments in the history of our planet and of a distant past in ancient oceans, streams and forests.  Changes in the ancient atmosphere are reflected in the molecules that allow our cells to cooperate to make bodies.  The environment of ancient streams shaped the basic anatomy of our limbs.  Our color vision and sense of smell has been molded by life in ancient forests and plains.  And the list goes on.  This history is our inheritance, one that affects our lives today and will do so in the future.”

The overarching story of Your Inner Fish is that of descent with modification.  We are modified descendents of our parents, as were they, as were their ancestors, back to the origin of life.

Neil Shubin, the paleontologist and anatomy professor who co-discovered a significant fossilized “intermediate” between fish and land-dweller, tells this story with humor and grace.  Anecdotes about particular scientists and their historic experiments infuse the whole book with a tone of enthusiastic discovery.

At first glance, parts of our bodies seem to make no sense at all.  Looking at the winding nerves in our heads, or at the circuitous route that sperm takes from scrotum to penis, our bizarre plumbing and circuitry calls to mind the wiring of an old building with new innovations added on or wound around defunct or outdated structures.  That’s exactly because the human body, 3.5 billion years in the making, was built in just that way. 

For example, Shubin tells, us, 3 percent of our entire genome is devoted to genes for detecting various odors, many of which are useless to us but may have been critical to our mammal ancestors’ survival.

Hiccups irk us, but this likely remnant from our amphibious past allows tadpoles to pump water without flooding their lungs.

Shubin tells stories about particular genes—including Sonic hedgehog that is crucial in the development of limbs, or Hox genes that control the organization of the body—which function similarly across various species, from humans to fruit flies, mice to sharks.  Various mad, Frankensteinish experiments have shown amazing results from the swapping of genes among them.

“The best road maps to human bodies lie in the bodies of other animals,” writes Shubin.  “…We are not separate from the rest of the living world; we are part of it down to our bones [and] even our genes.”

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