Studying the secrets of human evolution requires quite a road trip.

Every summer, Alyssa Crittenden flies into Arusha, Tanzania, loads up a Land Rover with food, water, spare tires, and a machete, and treks into the East African bush. Here, in an area anthropologists call the "Crucible of Human Evolution," she observes the Hadza, one of world's last groups of hunter-gatherers.

Just a few million years ago, our hominid ancestors took a leap forward in brain size. This coincided with changes in diet and reproduction. We're pretty much the only species that cares for offspring years after weaning and that has more babies before that last one is independent. This requires what Crittenden believes is the hallmark of humans: cooperation. "To figure out how nutrition, reproduction, and social behavior interact, I have to go into an area where these things are constantly at play."

The journey takes five hours on a paved road, another few hours on dirt roads, and then five more to hack through undergrowth off road. And that's only if she makes good time by avoiding punctured tires and quicksand -- "Before I went to Tanzania, I really thought that existed only in Tarzan movies."

The Bay Area native had never camped before spending 14 months in Hadza country in 2004 for her doctoral research. "If I'd known how risky it was, maybe I wouldn't have gone," she says. "I was afraid of the wrong things." She feared the bushwhacking but found that broken-down cars and donkey gatherings made the paved roads more treacherous. She was afraid to drink the water but failed to grasp the potential danger that encounters with displaced refugees or illegal poachers could bring.

She is one of only a handful of anthropologists documenting the ways of the Hadza. Through personal observations, she developed a theory on the role that honey, alongside meat, had in boosting our brainpower. Her ability to study the Hadza, however, is changing as they are displaced from their traditional lands. She expects their ways to die out within her lifetime. "With a small population of merely a thousand people, many might think that the importance of the Hadza is negligible compared to our huge society. As an anthropologist, however, I believe it's necessary to document their world before it's gone."

Crittenden's work is featured in the documentary The Hadza: Last of the First, now under consideration for the Sundance Film Festival.