February 18, 2008
The Evolution of Humans From the Sea to Couch Potatoes
Even before they are born, all people carry genetic baggage, genes that were useful to distant, non-human ancestors but are hopelessly outdated, even harmful, to humans as they live today.
Chicago scientist Neil Shubin calls this inheritance our "inner fish."
People hiccup, he explains, because of a design malfunction in a nervous system and breathing apparatus passed down from fish and tadpoles. Human males are vulnerable to hernias because of their awkward setup for toting around sperm-producing gonads, which developed in fish.
"In a perfectly designed world -- one with no history -- we would not have to suffer everything from hemorrhoids to cancer," Shubin writes in his new book, "Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body."
A dean at the University of Chicago and provost of the Field Museum, Shubin is part of a pioneering field that uses traditional paleontology and molecular biology to study evolution. At 47 he is already something of a science celebrity for helping discover what may be one of history's most important fossils: a "missing link" from the time animals first crawled out of the sea 370 million years ago.
The book may make him even more famous. Pantheon Books seems to have high hopes for "Your Inner Fish," with an announced first printing of 50,000 books, a coast-to-coast author tour and foreign publication rights sold to 13 nations so far. It even placed Shubin on the red-hot "Colbert Report," comedian Stephen Colbert's television show, the night before the book's Jan. 15 release.
While religious creationists doubt evolutionary theory and abhor the suggestion that humans are descended from apes, "Your Inner Fish" traces human evolution far beyond early primates.
"I wanted to tell the story of the human body from the really deep, ancient stuff -- fish, worms, jellyfish, sponges and those sorts of simpler, more primitive life forms," Shubin said recently as he showed off his genetic laboratory on the U. of C. campus.
Although his writing underscores the evidence for evolutionary theory, Shubin does not directly tackle the ongoing argument between scientists and those who say "intelligent design" is a credible alternative.
"I wanted to take the high road and show the joy, beauty and power of science," he said. "I didn't want to write a diatribe condemning creationists.
"I see science and religion being in two different spheres, so I am very careful that I never, ever tell people what to believe in. Of course I believe nobody should dictate their beliefs to me either."
'His success is no surprise'
Shubin, the son of noted crime novelist Seymour Shubin, graduated from high school in Philadelphia. He planned to become a veterinarian but then, as a freshman at Columbia University, took a class taught by British paleoanthropologist Ian Tattersall, a renowned expert on human evolution.
He was so intrigued, Shubin said, that he became "a real pain in the butt" to Tattersall, hanging around after class and showing up during Tattersall's office hours to badger him with questions.
"Of all the students in that class," Tattersall said in a telephone interview, "Neil is really the one I remember. It was unusual to have an undergraduate so deeply interested, and he was so busy on his own with so many projects. His success is no surprise at all to me."
Shubin went into developmental biology, a then-emerging field involving the use of powerful new, laboratory-based tools to follow evolutionary pathways of modern living organisms by studying their DNA. His doctoral thesis was on how cells come together to make a limb, a hand or a foot.
"But I loved expeditionary paleontology, too, going out searching for fossils, so I always made time for that," Shubin said.
On his first teaching job at the University of Pennsylvania, he pursued field expeditions and laboratory bench work.
"It was often hard for me to do both things," he said. "When I joined the faculty at Penn, I was told to lose paleontology and stick to developmental biology, that I'd be spread too thin doing both and wouldn't be taken seriously in either field."
But Tattersall said Shubin's dual approach now is fast becoming the norm for scientists tracking evolution.
"They are just tools, really," Tattersall said of fossil and molecular studies. "Everybody should have all those tools in his kit."
The U. of C. hired Shubin as chair of its organismal biology department in 2000, when the Field Museum also made him a research associate. In 2006 the university elevated him to associate dean of biological sciences, and the Field made him head of its science staff.
The 'missing link' fossil
That same year, Shubin cemented an international reputation when he and a group of young colleagues he had co-led since the early 1990s reported that they had found the "missing link" fossil.
For decades, paleontologists had speculated that ancient fish living in the Devonian period 415 million to 365 million years ago must have grown limbs to climb out of the water to become the first vertebrate land animals.
Unable to command much grant money when they started, Shubin and his colleagues first searched for fossil evidence of transitional water-to-land animals by following road-building crews that were cutting through 365 million-year-old Devonian formations in Pennsylvania.
They found a lot of fossils of early land animals but no fish with feet, so they decided to look a little earlier in time. A map turned up just what they wanted -- deposits 370 million to 375 million years old -- on islands far beyond the Arctic Circle in northern Canada.
In 1999, Shubin and his colleagues began looking. For several summers they found only fossil fish, but in 2004 they dug out several skeletons of a creature that had the gills and scales of a fish but also a neck and shoulders, arms, wrists and fingers.
This was the transitional animal they had been seeking. It could raise its head out of water, maybe even propel itself out of water onto land to chase insects to dine upon. Called Tiktaalik, the creature made front-page news in 2006.
Suited for hunter-gatherers
Fossil findings like Tiktaalik help map out the evolutionary changes that led from fish to early amphibians to dinosaurs, mammals and humans. But, as Shubin points out in his book, the evidence is also right under our noses.
"We can see in our own bodies the evidence of how evolution took twists and turns that leave us with a body that makes us vulnerable to disease and damage," he said.
Our physiological design, Shubin added, is for the constant, strenuous physical activities of our hunter-gatherer forebears, while modern society has humans living "the lifestyle of a spud."
In the "feast-or-famine" days of early humans, a tendency to store fat in bodies was beneficial. But in modern times of constant bounty, it just makes people obese and vulnerable to fatal heart diseases, cancers and strokes, not to mention bad backs and blown knees.
Hunter-gatherers may not have suffered many hemorrhoids, but truck drivers and desk jockeys who spend eight or more hours a day sitting suffer from them plenty.
"We were not designed to live past the age of 80, sit on our keisters for 10 hours a day, and eat Hostess Twinkies," Shubin writes.