Handy Genes
w hile my colleagues and I were digging up the first Tiktaalik in the Arctic in July 2004, Randy Dahn, a researcher in my laboratory, was sweating it out on the South Side of Chicago doing genetic experiments on the embryos of sharks and skates, cousins of stingrays. You've probably seen small black egg cases, known as mermaid's purses, on the beach. Inside the purse once lay an egg with yolk, which developed into an embryonic skate or ray. Over the years, Randy has spent hundreds of hours...
The development of a limb in this case a chicken wing All of the key stages in
To study how this pattern emerges, we need to look at embryos and sometimes interfere with their development to assess what happens when things go wrong. Moreover, we need to look at mutants and at their internal structures and genes, often by making whole mutant populations through careful breeding. Obviously, we cannot study humans in these ways. The challenge for the pioneers in this field was to find the animals that could be useful windows into our own development. The first experimental...
Seeing The Fish
In Owen and Darwin's day, the gulf between fins and limbs seemed impossibly wide. Fish fins don't have any obvious similarities to limbs. On the outside, most fish fins are largely made up of fin webbing. Our limbs have nothing like this, nor do the limbs of any other creature alive today. The comparisons do not get any easier when you remove the fin webbing to see the skeleton inside. In most fish, there is nothing that can be compared to Owen's one bone-two bones-lotsa blobs-digits pattern....
Digging Fossilsseeing Ourselves
I first saw one of our inner fish on a snowy July afternoon while studying 375-million-year-old rocks on Ellesmere Island, at a latitude about 80 degrees north. My colleagues and I had traveled up to this desolate part of the world to try to discover one of the key stages in the shift from fish to land-living animals. Sticking out of the rocks was the snout of a fish. And not just any fish a fish with a flat head. Once we saw the flat head we knew we were on to something. If more of this...
Chapter Two
I mages of the medical school anatomy lab are impossible to forget. Imagine walking into a room where you will spend several months taking a human body apart layer by layer, organ by organ, all as a way to learn tens of thousands of new names and body structures. In the months before I did my first human dissection, I readied myself by trying to envision what I would see, how I would react, and what I would feel. It turned out that my imagined world in no way prepared me for the experience. The...
This is where we work southern Ellesmere Island in Nunavut Territory Canada
Failure again all the fish we were finding were well-known species that had been collected in sites of a similar age in Eastern Europe. To top it off, these fish weren't very closely related to land-living animals. In 2004, we decided to give it one more try. This was a do-or-die situation. The Arctic expeditions were prohibitively expensive and, short of a remarkable discovery, we would have to call it quits. Everything changed over a period of four days in early July 2004. I was flipping rock...
This figure says it all Tiktaalik is intermediate between fish and primitive
As the discoverers of the creature, Ted, Farish, and I had the privilege of giving it a formal scientific name. We wanted the name to reflect the fish's provenance in the Nunavut Territory of the Arctic and the debt we owed to the Inuit people for permission to work there. We engaged the Nunavut Council of Elders, formally known as the Inuit Qaujimajatuqangit Katimajiit, to come up with a name in the Inuktitut language. My obvious concern was that a committee named Inuit Qaujimajatuqangit...
Tracing arm bones from fish to humans
I can do a similar analysis for the wrists, ribs, ears, and other parts of our skeleton all these features can be traced back to a fish like this. This fossil is just as much a part of our history as the African hominids, such as Australopithecus afarensis, the famous Lucy. Seeing Lucy, we can understand our history as highly advanced primates. Seeing Tiktaalik is seeing our history as fish. So what have we learned Our world is so highly ordered that we can use a walk through a zoo to predict...
Along the roads in Pennsylvania we were looking at an ancient river delta much
After the discovery of Hynerpeton and other fossils from these rocks, Ted and I were champing at the bit for better-exposed rock. If our entire scientific enterprise was going to be based on recovering bits and pieces, then we could address only very limited questions. So we took a textbook approach, looking for well-exposed rocks of the right age and the right type in desert regions, meaning that we wouldn't have made the biggest discovery of our careers if not for an introductory geology...
Finding Your Inner Fish
T ypical summers of my adult life are spent in snow and sleet, cracking rocks on cliffs well north of the Arctic Circle. 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. Ancient fish bones can be a path to knowledge about who we are and how we got that way. We learn about our own bodies in seemingly bizarre places, ranging from...