Humans are not fish. But the two very different species share a genetic toolkit that determines all sorts of crucial traits. So studying fish can teach us important things about ourselves.
David Kingsley is a geneticist at Stanford University. He’s interested in how genes changed over the course of human evolution.
Kingsley says it’s important to think of humans as part of a bigger picture.
Humans, says Kingsley, are part of “the large branching set of relationships that is what’s produced all the organisms we see around us.”
Humans Came From Fish
To get a better idea of how humans emerged out of these branching relationships, Kingsley has turned to fish, and to one fish in particular: the stickleback.
“We didn’t choose them because we wanted to understand sticklebacks themselves,” says Kingsley. “We chose them because they’re a model that makes the process of evolution something that can be dissected and taken apart in the lab.”
Until about 15,000 years ago, sticklebacks lived in the ocean, and they all pretty much looked the same. But 15,000 years ago an ice age was ending and glaciers were receding, creating a variety of new environments for the fish. The sticklebacks evolved a variety of new colors and shapes as they adapted to their new homes.
Kingsley figured if he could find the genes that caused those changes to take place, that might tell him how human color and shape evolved.
To find the genes, he breeds the small fish in 30-gallon tanks in the basement of the Stanford Medical School. Kingsley has collected sticklebacks from around the world – big ones, small ones, brown ones, white ones. By breeding big ones with small ones, white ones with green ones, he can follow genes for color and size through successive generations and zero in on the ones he’s interested in.
Recently, Kingsley says, he found the genes responsible for stickleback color. And that’s an important step, because when humans left Africa about 100,000 years ago, they too started evolving new colors.
And humans, as it turns out, have very similar versions of each of these genes.
“Fish are not humans, but humans came from fish,” says Kingsley. “And that relationship is probably the reason that the mechanisms discovered in one organism are often predictive of what happens in other organisms.”
So Kingsley looked to see if the same genes played the same role in human coloration. Early results suggest they do. Like fish, humans have also evolved a variety of skin colors that are striking and easy to recognize.
“And it turns out to involve exactly the same genes and exactly the same mechanisms that are involved in the stickleback,” Kingsley says.
This is a theme in Kingsley’s work, and in evolution in general.
If something works in one organism – say the genes for controlling skin color – it tends get passed on to that organism’s evolutionary descendants. So it’s not surprising the same genes play the same role in humans and fish. We all share a genetic toolkit that gets used over and over, just in slightly different ways. Not just for skin color, but for all sorts of crucial traits.
But somehow, these small changes in our genes, and the way they switch on and off, can result in big effects. For us, it meant language and big brains. And that lets us do things other species can’t.
“We build the cities, we do radio shows, we have the technology and the ability to communicate and interact and study ourselves and where we came from,” says Kinglsey.
“That’s unique to humans. We’re studying the sticklebacks, the sticklebacks aren’t studying us.”
At least we don’t think they are.