By DAVID DOBBS  l  National Geographic January 2013

Not all of us ache to ride a rocket or sail the infinite sea. Yet as a species we’re curious enough, and intrigued enough by the prospect, to help pay for the trip and cheer at the voyagers’ return. Yes, we explore to find a better place to live or acquire a larger territory or make a fortune. But we also explore simply to discover what’s there.

“No other mammal moves around like we do,” says Svante Pääbo, a director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, where he uses genetics to study human origins. “We jump borders. We push into new territory even when we have resources where we are. Other animals don’t do this. Other humans either. Neanderthals were around hundreds of thousands of years, but they never spread around the world. In just 50,000 years we covered everything. There’s a kind of madness to it. Sailing out into the ocean, you have no idea what’s on the other side. And now we go to Mars. We never stop. Why?”

Why indeed? Pääbo and other scientists pondering this question are themselves explorers, walking new ground. They know that they might have to backtrack and regroup at any time. They know that any notion about why we explore might soon face revision as their young disciplines—anthropology, genetics, developmental neuropsychology—turn up new fundamentals. Yet for those trying to figure out what makes humans tick, our urge to explore is irresistible terrain. What gives rise to this “madness” to explore? What drove us out from Africa and on to the moon and beyond?

If an urge to explore rises in us innately, perhaps its foundation lies within our genome. In fact there is a mutation that pops up frequently in such discussions: a variant of a gene called DRD4, which helps control dopamine, a chemical brain messenger important in learning and reward. Researchers have repeatedly tied the variant, known as DRD4-7R and carried by roughly 20 percent of all humans, to curiosity and restlessness. Dozens of human studies have found that 7R makes people more likely to take risks; explore new places, ideas, foods, relationships, drugs, or sexual opportunities; and generally embrace movement, change, and adventure. Studies in animals simulating 7R’s actions suggest it increases their taste for both movement and novelty. (Not incidentally, it is also closely associated with ADHD.)

Most provocatively, several studies tie 7R to human migration. The first large genetic study to do so, led by Chuansheng Chen of the University of California, Irvine in 1999, found 7R more common in present-day migratory cultures than in settled ones. A larger, more statistically rigorous 2011 study supported this, finding that 7R, along with another variant named 2R, tends to be found more frequently than you would expect by chance in populations whose ancestors migrated longer distances after they moved out of Africa. Neither study necessarily means that the 7R form of the gene actually made those ancestors especially restless; you’d have to have been around back then to test that premise with certainty. But both studies support the idea that a nomadic lifestyle selects for the 7R variant.

Another recent study backs this up. Among Ariaal tribesmen in Africa, those who carry 7R tend to be stronger and better fed than their non-7R peers if they live in nomadic tribes, possibly reflecting better fitness for a nomadic life and perhaps higher status as well. However, 7R carriers tend to be less well nourished if they live as settled villagers. The variant’s value, then, like that of many genes and traits, may depend on the surroundings. A restless person may thrive in a changeable environment but wither in a stable one; likewise with any genes that help produce the restlessness.

So is 7R the explorer’s gene or adventure gene, as some call it? Yale University evolutionary and population geneticist Kenneth Kidd thinks that overstates its role. Kidd speaks with special authority here, as he was part of the team that discovered the 7R variant 20 years ago. Like other skeptics, he thinks that many of the studies linking 7R to exploratory traits suffer from mushy methods or math. He notes too that the pile of studies supporting 7R’s link with these traits is countered by another stack contradicting it.

“You just can’t reduce something as complex as human exploration to a single gene,” he says, laughing. “Genetics doesn’t work that way.”

Better, Kidd suggests, to consider how groups of genes might lay a foundation for such behavior. On this he and most 7R advocates agree: Whatever we ultimately conclude about 7R’s role in driving restlessness, no one gene or set of genes can hardwire us for exploration. More likely, different groups of genes contribute to multiple traits, some allowing us to explore, and others, 7R quite possibly among them, pressing us to do so. It helps, in short, to think not just of the urge to explore but of the ability, not just the motivation but the means. Before you can act on the urge, you need the tools or traits that make exploration possible.

Fortunately for me, I had to wander only a floor down from Kidd’s office to find someone who studies such tools: developmental and evolutionary geneticist Jim Noonan. His research focuses on the genes that build two key systems: our limbs and our brains. “So I’m biased,” he says, when I press him about what makes us explorers. “But if you want to boil this down, I’d say our ability to explore comes from those two systems.”

The genes that build our human limbs and brains, Noonan says, are pretty much the same as those that build the same parts of other hominids and apes. Each species’ limbs and brains end up different largely because the construction projects directed by these developmental genes start and stop at different times. In humans the result is legs and hips that let us walk long distances; clever, clever hands; and an even cleverer brain that grows far more slowly but much larger than other ape brains. This triad separates us from other apes and, in small but vital developmental details, from other hominids.

Together, says Noonan, these differences compose a set of traits uniquely suited for creating explorers. We have great mobility, extraordinary dexterity, “and, the big one, brains that can think imaginatively.” And each amplifies the others: Our conceptual imagination greatly magnifies the effect of our mobility and dexterity, which in turn stirs our imaginations further.

“Think of a tool,” says Noonan. “If you can use it well and have imagination, you think of more applications for it.” As you think of more ways to use the tool, you imagine more goals it can help you accomplish.

This feedback loop, Noonan points out, helped empower the great Anglo-Irish explorer Ernest Shackleton—and saved him when he and his crew were stranded on Elephant Island in 1916. After polar ice crushed their ship, Shackleton, 800 miles from anywhere with 27 exhausted men, little food, and three small open boats, conceived an insanely ambitious sea voyage. Using a handful of basic tools to modify a 22-foot lifeboat, the James Caird (another tool), for a task absurdly beyond its original design, he gathered his navigational instruments and five of his men and executed a trip that few would dare imagine. He reached South Georgia, then returned to Elephant Island to rescue the rest of the crew.

Shackleton’s adventure shows starkly, says Noonan, a dynamic that has driven human progress and exploration from the start: As we leverage dexterity with imagination, we create advantages “that select for both traits.”

Noonan makes a good case that our big brain and clever hands build a capacity for imagination. Alison Gopnik, a child-development psychologist at the University of California, Berkeley, says humans also possess another, less obvious advantage that fosters that imaginative capacity: a long childhood in which we can exercise our urge to explore while we’re still dependent on our parents. We stop nursing roughly a year and a half sooner than gorillas and chimps, and then take a far slower path to puberty—about a decade, compared with the three to five years typical for gorillas and chimps. Dental evidence from Neanderthals suggests they too grew up faster than we do. As a result, we have an unmatched period of protected “play” in which to learn exploration’s rewards.

Many animals play, says Gopnik. Yet while other animals play mainly by practicing basic skills such as fighting and hunting, human children play by creating hypothetical scenarios with artificial rules that test hypotheses. Can I build a tower of blocks as tall as I am? What’ll happen if we make the bike ramp go even higher? How will this schoolhouse game change if I’m the teacher and my big brother is the student? Such play effectively makes children explorers of landscapes filled with competing possibilities.

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