As we will explore in the human evolution chapters to come, the human line split from a common ancestor that we share with the African apes. Although this split occurred millions of years ago, paleoanthropologists in the mid-20th century were hopeful that observations made among the living apes might shed light on the lifeways of the fossil species they were discovering. Louis Leakey encouraged Jane Goodall to begin her research with chimpanzees in
Combe Stream Chimpanzee Reserve (now a national park) on the eastern shores of Lake Tanganyika in Tanzania for this reason.
But the forest ape behavior model appeared flawed to the paleoan-thropologists of the past.
The fossil evidence indicated that the earliest human ancestors inhabited a grassy savannah environment rather than the tropical forests inhabited by the apes. Instead, paleoanthropologists turned to baboons: a group of Old World monkey species that inhabit the savannah environments of eastern Africa where the richest fossil evidence of our ancestors had also been found. While the savannah environment has certainly been important in human evolution, recent fossil discoveries and analyses have lead paleoanthropologists back into the forest. The earliest twolegged ancestors inhabited a forested environment and have lead paleoanthropologists to investigate the human origins in terms of the transition from forest to savannah.
Though baboons differ considerably from our twolegged ancestors, their survival strategies provide some clues as to how our ancestors adapted to the savannah environment. Members of the genus Papio, baboons are among the largest of the Old World monkeys. Fully terrestrial, troops of baboons can be seen sitting together on the dry savannah earth to forage for corms (thick, nutritious underground reproductive parts of plants). They keep a watchful eye out for predators while feeding. At the first sight or sound of danger, alarm calls by members of the troop will signal for all the individuals to retreat to safety.
Baboons live in groups that vary dramatically in size, from under ten to hundreds of individuals. In some species the groups are multi-male multi-female while others are made up of a series of harems—one male with several females that he dominates. Sexual dimorphism—anatomical differences between males and females—is high in baboons, and therefore males can use their physical advantages to overpower females easily. But the degree to which males choose to do so varies from group to group.
Extrapolating from baboons to theories about our ancestors poses problems. To use the words of primatologists Shirley Strum and William Mitchell, these baboon “models” often became baboon “muddles.”38 Paleoanthropologists
The behavior of baboons, a type of Old World monkey, has been particularly well studied. There are several distinct species of baboon, each with their own social rules. In troops of hamadryas baboons (pictured), the sacred baboons of ancient Egypt, each male has a harem of females over which he dominates. Female hamadryas baboons, if transferred to a troop of olive baboons, where females are less submissive, maintain the passive behaviors learned in their original troop. But a female olive baboon placed in the hamadryas troop quickly learns submissive behaviors in order to survive.
Did not expect our ancestors to possess tails or ischial callosities—the hardened, nerveless buttock pads that allow baboons to sit for long periods of time. Tails are strictly a monkey characteristic, not an ape one, and among the hominoids, only gibbons and siamangs possess ischial callosities. Instead, paleoanthropologists looking for evolutionary information were trying to piece together examples of convergence—of behaviors that might appear in largebodied, dimorphic primates living in large multi-male multi-female groups in a savannah environment.
The upside of paleoanthropology’s “baboon hypothesis” is that it led to many excellent long-term field studies of baboons that have yielded fascinating data on their social organization, omnivorous diet, mating patterns and other reproductive strategies, communication, and so forth. As with most primate field studies, the evolutionary questions remain in the background while the rich repertoire of primate behavior takes center stage.
World History
