the human edge - finding our inner fish

NPR | It took him years of searching in the Canadian Arctic, but in 2004, Neil Shubin found the fossilized remains of what he thinks is one of our most important ancestors.

Turns out, it's a fish.

Shubin says his find, which he named Tiktaalik, represents an important evolutionary step, because it has the structures that will ultimately become parts of our human bodies. Shoulders, elbows, legs, a neck, a wrist — they're all there in Tiktaalik.

"Everything that we have are versions of things that are seen in fish," says Shubin.

Of course, there are things that we have that Tiktaalik doesn't.

"We have a big brain, and portions of that big brain are not seen in Tiktaalik," says Shubin. "But the template, all the way down to the DNA that builds it, is already present in creatures like this."

Inside this fish, Shubin sees us.

"It's like peeling an onion," he says. "Layer after layer after layer is revealed to you. Like in a human body, the first layer is our primate history, the second layer is our mammal history, and on and on and on and on, until you get to the fundamental molecular and cellular machinery that makes our bodies and keeps are cells alive, and so forth."

Our Inner Yeast
In fact, not only are we related to an ancient fish, but many of the parts critical for making yeast are also critical for making us, says Gavin Sherlock, a geneticist at Stanford University.

"About one-third of the yeast genes have a direct equivalent version that still exists in humans," he says.

Sherlock says that not only do many of the same genes still exist in humans and yeast, but they're so similar that you can exchange one for the other.

"There are several hundred examples where you can knock out the yeast gene, put in the human equivalent, and it restores it back to normal," he says.

Think about it, he says: We have a lot in common with yeast. Yeast consume sugars like we do, yeast make hormones like we do, and yeast have sex — not quite like we do, but sex.

Sex isn't just fun and games. Sexual reproduction is critical for stirring the genetic pot, speeding the evolution of endless forms most beautiful, from fruit flies to blue whales to humans.

Now yeast is a single-celled organism. We have trillions and trillions of cells in our bodies — different kinds of cells, all fitting together. How did that happen?

The answer is at the Field Museum in Chicago.