### Becoming a Benign Dominant

To track how humans became Earth's dominant animal, Ehrlich began with a photo of a tarsier in a tree. The little primate had a predator's binocular vision and an insect-grabber's fingers. When (possibly) climate change drove some primates out of the trees, they developed a two-legged stance to get around on the savanna. Then the brain swoll up, and the first major dominance tool emerged--language with syntax.

About 2.5 million years ago, the beginnings of human culture became evident with stone tools. "We don't have a Darwin of cultural evolution yet," said Ehrlich. He defined cultural evolution as everything we pass on in a non-genetic way. Human culture developed slowly-the stone tools little changed from millennium to millennium, but it accelerated. There was a big leap about 50,000 years ago, after which culture took over human evolution--our brain hasn't changed in size since then.

With agriculture's food surplus, specialization took off. Inuits that Ehrlich once studied had a culture that was totally shared; everyone knew how everything was done. In high civilization, no one grasps a millionth of current cultural knowledge. Physicists can't build a TV set.

Writing freed culture from the limitations of memory, and burning old solar energy (coal and oil) empowered vast global population growth. Our dominance was complete. Ehrlich regretted that we followed the competitive practices of chimps instead of bonobos, who resolve all their disputes with genital rubbing.

"The human economy is a wholly-owned subsidiary of the Earth's natural systems," said Ehrlich, and when our dominance threatens the ecosystem services we depend on, we have to understand the workings of the cultural evolution that gave us that dominance. The current two greatest threats that Ehrlich sees are climate change (10 percent chance of civilization ending, and rising) and chemical toxification of the biosphere. "Every cubic centimeter of the biosphere has been modified by human activity."

The main climate threat he sees is not rising sea levels ("You can outwalk that one") but the melting of the snowpack that drives the world's hydraulic civilizations-- California agriculture totally dependent on the Sierra snowpack, the Andes running much of Latin America, the Himalayan snows in charge of Southeast Asia. With climate in flux, Ehrlich said, we may be facing a millennium of constant change. Already we see the outbreak of resource wars over water and oil.

He noted with satisfaction that human population appears to be leveling off at 9 to 10 billion in this century, though the remaining increase puts enormous pressure on ecosystem services. He's not worried about depopulation problems, because "population can always be increased by unskilled laborers who love their work."

The major hopeful element he sees is that cultural evolution can move very quickly at times. The Soviet Union disappeared overnight. The liberation of women is a profound cultural shift that occurs in decades. Facing dire times, we need to understand how cultural evolution works in order to shift our dominance away from malignant and toward the benign.

In the Q & A, Ehrlich described work he's been doing on cultural evolution. He and a graduate student in her fifties at Stanford have been studying the progress of Polynesian canoe practices as their population fanned out across the Pacific. What was more conserved, they wondered, practical matters or decoration? Did the shape of a canoe paddle change constantly, driven by the survival pressure of greater efficiency, or did the carving and paint on the paddles change more, driven by the cultural need of each group to distinguish itself from the others.

Practical won. Once a paddle shape proved really effective, it became a cultural constant.