Do Polish Tracks Trump Tiktaalik?

A bit of a firestorm with local significance was stirred up this week when a paper published in Nature purported to reset the clock on when marine animals took their first step out of water. Grzegorz Niedzwiedzki and colleagues from Warsaw and Sweden presented a fossil “trackway” made up of what the team identified as several hand and footprints from a tetrapod four-limbed vertebrates thought to be a key step in evolution from marine animals to land dwellers. The tracks, found in south-eastern Poland in a layer dated as 395 million years old (video), reveal some fascinating details in the authors’ analysis, including distinct hand and foot prints, toes and ankles - all critical aspects of the transition from fin to limb. It’s also the earliest known evidence for a tetrapod, predating fossil findings of “fish-with-limbs” such as Tiktaalik by nearly 20 million years.

While some are convinced of these conclusions, others are skeptical. Tiktaalik, discovered in 2004 in far northern Canada by a team led by University of Chicago paleontologist Neil Shubin, remains the earliest known tetrapod fossil, a remarkably complete specimen that clearly shows limb-like bone structure. Footprints, on the other hand, are acceptable as paleontological evidence, but much more open to question. Indeed, no tetrapod fossils - or any fossils, for that matter - were found near the trackway, which the authors attribute to the soil being a poor environment for preserving skeletons. Nevertheless, in a news article accompanying the Nature paper, other paleontologists express caution in accepting the veracity of the trackway fossil, and Phillippe Janvier of the Muséum National d’Histoire Naturelle in Paris suggested “a risk” that natural processes could have produced track-like markings.

Shubin, currently on sabbatical writing the follow-up to this award-winning Your Inner Fish, wasn’t immediately available for comment. But when he’s back, ask him what he thinks of the new discovery and how it changes our view of early tetrapod evolution.

The Cell Phone Treatment

In an almost too-weird-to-be-true piece of science news this week, a story started kicking around that the type of electromagnetic fields (EMFs) generated by cell phones was found to be effective at protecting against or even reversing the effects related to Alzheimer’s disease in mice. Studies of cell phone radiation - usually focused on proving that the phones’ electromagnetic waves cause harm - are notoriously unreliable. Time and again, studies have shown these waves do not cause brain tumors or other diseases…but in looking for damage from cell phone use, were scientists overlooking benefits?

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4:15 p.m. - Of Mice and Mammoths

The last talk of the day (for me, as I had to leave before the final, final talk) made for a great reminder of how far the field of evolutionary biology, wrapped in a relatively simple story told engagingly by Hopi Hoekstra of Harvard. Hoekstra described her research quest as “the hunt for genes that make a difference,” and she uses a really nice model system - the oldfield mice of the southern United States. These mice typically are brown in color, but they have migrated in the recent (meaning thousands) of years to the gulf and atlantic coasts and taken up residence, like a retired couple, on the beach. But a brown mouse on a beach is a target, and their predators, which include birds and coyotes, find it all to easy to locate their brown fur on white sand and make a beachside snack out of them.

Cue natural selection - soon you have brown oldfield mice inland, and predominantly white oldfield mice that live on the beach. Hoekstra tested whether the fur color really does construe an evolutionary advantage with a simple experiment - make a bunch of clay mice colored brown or white, and leave them out on the beach. Sure enough, the brown clay mice quickly showed divots and bitemarks left by attacks from (presumably very frustrated) predators.

That would have been a fine experiment for the 1959 conference, but Hoekstra’s next step was pure 2009 - she took examples of brown and white mice back to the lab, bred them, and searched for the genes that determined fur color. Her laboratory narrowed the gene candidates down to three genes, and in one of them - a receptor called Mc1r - the substitution of a single amino acid flipped the switch from brown fur to white fur. Amazingly, when another group of scientists sequenced the genome of extinct mammoths in 2006, they found the same amino-acid substitution in the same gene, implying that mammoths, like the oldfield mice, came in different color varieties.

After so much high theory and methodological complexity, Hoekstra’s experiment sent all of us (or at least me) home with a warm feeling - not only was her experiments a beautiful example of evolutionary biology that would have been impossible in 1959, it was a great example of teachable science, the kind of story that a 3rd-grader could wrap their head around and begin to see the truth of evolution. The cloud hanging over Darwin/Chicago 2009 was the uneasy feeling that all this scientific progress was still losing out in the arena of public opinion, but Hoekstra’s work and charismatic speaking style (on the heels of similar ambassador figures Neil Shubin and Michael Shue) chased away some of the pessimism, and left me confident that the more examples we find of Darwin’s elegant theory at work in nature, the easier it will be to convince the world that it is true.

And with that, we’re finished. Happy Halloween to those of you who have followed me this far, and thanks very much for reading and perhaps linking to the posts. I’ll be back Monday with a digest post to help navigate the coverage of the last few days, and Jeremy Manier will be here Tuesday with his own thoughts on the conference.

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Whenever I see a drawing of Tiktaalik like the one above, I always think “Man, that walking fish sure looks snooty.” But Tiktaalik roseae, discovered in 2004 by University of Chicago evolutionary biologist Neil Shubin and his team in the Canadian Arctic, is worthy of its haughty air. For one thing, the “fishapod” had a neck, a feature you don’t typically find on a fish, and the explanation for its stuck-up posture. Tiktaalik’s limbs were even more unusual and exciting, as Shubin found bones that were more like fingers than the tiny bones typically seen in fish fins. These structures meant Tiktaalik held a very important place in the tree of life, one of the elusive transitional species (in this case between fish and amphibians) that evolutionary biologists dream of discovering.

Shubin’s book about Tiktaalik and how it demonstrates the process of evolution, Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body, was released almost two years ago. Perhaps it takes scientists a while to squeeze in some non-journal reading time, because the book (now in paperback, cough plug cough) was today named as the 2009 book of the year by the National Academy of Sciences. Here’s what they said:

Neil Shubin for his delightful, intellectually challenging view of evolution from primitive fish to humans by a scientist who finds fossils in the most uncomfortable places and chronicles it all in Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body (Pantheon Books).

Your Inner Fish was also on the shortlist for this year’s Royal Society Prize for Science Books, in the esteemed company of science writers such as Carl Zimmer, Leonard Mlodinow and Ben Goldacre.

UPDATE: You can read an online excerpt from Your Inner Fish, thanks to University of Chicago Magazine!

Shubin is as good a public speaker as he is a writer. As probably the only fish paleontologist who teaches anatomy to medical students (here at the Pritzker School of Medicine), Shubin uses evolutionary theory to explain the stranger features of the human body. I caught an excellent lecture from him at the AAAS Meeting this past February (my favorite quote: “When I look at a human being, what I see is a giant, morphed-up fish.”), and he came off like a seasoned television pro on the Colbert Report. If you’d like to see Shubin live and in person, he is one of several speakers at the star-studded Darwin Conference taking place October 29-31 at the University of Chicago to celebrate the 150th anniversary of The Origin of the Species.

For a little teaser, here’s some video taken by Jeremy Manier earlier this year of Shubin talking about how cartoons and toys mischaracterize the process of evolution.

This blog will cover a lot of research that happens beyond the walls of this university, but with some of the world’s leading authorities on Darwin and evolutionary biology just a short walk away, I wanted to collect some of their thoughts about Darwin Day.

Here’s Neil Shubin, bestselling author of “Your Inner Fish” and leader of a team that made one of the great paleontological finds in recent history - Tiktaalik roseae, also called the ”fishapod.” Neil keeps a funny little Darwin toy in his office that he uses to explain a central misconception about evolution - the idea that evolution always progresses toward ever greater complexity.