Pruetz Presidential Lecture explores human evolution through savanna chimps

AMES, Iowa -- As an anthropologist, Jill Pruetz says she is gaining a unique insight into human evolution through her study of savanna chimpanzees in southeastern Senegal. And she's not alone.

Her discovery that the chimps at her Fongoli site are the first non-humans to routinely use primitive spear-shaped tools to hunt other vertebrates rocked the science world two years ago.

In a new paper, the Iowa State University associate professor reports that the same chimps are now sharing food and hunting tools -- documenting another uncommon chimpanzee behavior previously considered by many scholars to be a defining human characteristic.

Pruetz will discuss those discoveries and more in the Spring 2009 Presidential University Lecture at Iowa State on Monday, March 2. Her presentation, titled "Savanna Chimpanzees and Our Understanding of Human Evolution," will begin at 8 p.m. in the Memorial Union Sun Room. The event is free and open to the public. A reception and poster display of student research will precede the lecture at 7 p.m. in the South Ballroom.

"Anthropologists study primates to get a better understanding of human evolution," said Pruetz. "So by comparing the chimps I study with the chimps in the forest and seeing those differences -- especially where they coincide with human behavior -- leads you to think that this (savanna) environment can produce some changes that take them in a human-like direction. No one ever assumes that chimps will become human, but these stresses (from the extreme hot, arid environment) result in things that are along the lines of what we predict happened with early hominids -- apes that lived six million years ago."

Sharing the news on sharing chimps

In her latest study, which she'll discuss in the lecture, Pruetz reports that male chimpanzees shared plant foods and tools with an unrelated female, who was not looking to mate. Both the males and females also shared their meat, an uncommon sharing behavior when dominant males are involved.

"With chimps, you do see sharing with meat. But at other sites, if females have the meat -- and they don't hunt at others' sites like they do mine -- males will take it (the meat) away from them," Pruetz said. "So really it's more tolerance and affiliation in this case."

Pruetz documents a number of plant sharing events between a young adult female, Tumbo, and dominant males at her Fongoli site. She reports that passive sharing occurred in all cases, with Tumbo approaching the males and taking the fruit from them without the males attempting to stop her.

Nineteen meat-sharing events were also documented by Pruetz in her paper, as well as two cases of tool sharing between Tumbo and adolescent males.

Previous research, including a 1986 book by famed primatologist Jane Goodall, reported that meat-sharing among chimps is thought to benefit the donor through reciprocity or trade -- such as the "meat for sex" hypothesis. But that couldn't be the case at the Fongoli site.

"She (Tumbo) was not in estrus when this (the food-sharing) was going on, so you can't say that she was using her state, or her pheromones. It was past that (period)," she said. "If anything, she was coming down off of that status. To me, it reflects the relationship they have with her, or she has with them."

Other "hot" talking points

In her lecture, Pruetz will also report on another paper she's authored on the chimpanzees' reaction to fire. And she plans to share the heartwarming story and video that she shot earlier this month when she helped to reunite a 9-month-old chimpanzee -- who had been taken by hunters at her Fongoli site -- with her mother.

"I plan to share an overview of what I've observed in the chimpanzees from my Fongoli site, including pictures and some video clips," said Pruetz, a National Geographic Emerging Explorer for 2008. "It should highlight some of the near- human behavior we've reported seeing the chimps exhibit."

Her discovery that chimps are using spear-shaped tools to hunt smaller primates (bush babies) was ranked second among Wired News' "Top 10 Scientific Breakthroughs of 2007," and featured prominently last year in "Ape Genius," a Nova/National Geographic Television Special that aired on PBS on the Nova series. It also was the subject of a feature story in National Geographic magazine.

Pruetz recently founded "Neighbor Ape," a nonprofit dedicated to the conservation of chimpanzees in Senegal. She has also conducted fieldwork with other primates such as spider monkeys, howling monkeys and tamarins in such countries as Peru, Costa Rica, Nicaragua and Kenya.

Her research is supported by grants from the National Geographic Society, National Science Foundation, Leakey Foundation, U.S. Fish and Wildlife Great Ape Conservation Grant, Great Ape Trust of Iowa, Primate Conservation Inc. and Iowa State University.

ISU President Gregory Geoffroy created the Presidential University Lecture Series in 2003 to highlight the expertise and excellence of Iowa State faculty.