Emory Report

July 10, 2000

Volume 52, No. 37

Scholarship & Research Whitten studies behavior, hormones in lemurs By Paul Thacker At the last turn of the century, most anthropologists thought human behavior was nothing more than an expression of innate drives. But radicals like Margaret Mead later disputed this theory, claiming that behavior was caused by socialization. What both sides of the debate lacked was convincing either way. To find this evidence, some researchers focus on nonhuman primates. For example, Pat Whitten is currently studying a type of lemur called sifakas to understand how hormones and behavior interact. Historically, people looked at androgens, such as testosterone, to determine rank. A deterministic model arose from these studies claiming that testosterone drove behavior. However, closer examination showed a contradiction. "In fact, testosterone responds as much to social setting as it drives behavior," said Whitten, associate professor of anthropology. This has led to more dynamic research focusing on testosterone level as a mirror of success and defeat in social interactions. Comparisons between different species point to the complex interplay of hormones and behavior. Hamadryas baboons form harems with one male aggressively guarding multiple females. This allows the dominant male sole access to mating rights, ensuring that his genes are passed on to the next generation. A closely related species, the Anubis baboon, lives in a more egalitarian social system with multiple males and females residing in the same troop. Dominant males will only guard a female when she is in estrus and ready to breed. These contrasts in social order are interesting, but there are also telling differences in their hormonal levels. Hama-dryas constantly maintain high levels of testosterone, while the Anubis' levels only increase during female estrus. So the Anubis' testosterone level is much more context dependent. "This is the male perspective of the world-what gets him aggravated," Whitten said. The sifakas Whitten studies are unique primates that live on Madagascar, off the southeastern coast of Africa. Having split from the primate evolutionary tree many millions of years ago, lemurs have diversified and, like monkeys, now occupy many different ecological niches. Whitten's project has four phases, and she just completed the initial study of male behavior and testosterone levels found in the feces. "Our long-term goal is to determine what makes males successful and what their testosterone and aggression have to do with that," she said. Whitten's study covered the period after females had given birth, so she expected male hormonal levels to fall. However males who moved between different groups maintained high testosterone levels, probably because they were experiencing stress. She also noticed one instance of a dominant male responding to a newcomer. When a new male enters a troop, it would be expected for the dominant male to respond aggressively to protect infants. In many species, new males will often kill babies that are not their own. This will cause the mother to go back into heat to be bred by the newcomer, ensuring that his genes are passed along to the next generation. Some would argue that this means evolution favors aggressive males. During the encounter Whitten witnessed, the new male entered a troop and the dominant male remained calm, showing no change in behavior or aggressiveness. But there was an increase in testosterone. "So there's no change in behavior, but their hormones are going nuts," she said. "That suggests that we need to look a little more closely at the subtleties of behavior, since the hormones give clues as to how the animals are interpreting different events." Beyond these issues involving rank and what she describes as "the male perspective of the world," Whitten is beginning to see a new direction for research. She has noticed instances where expected responses do not occur. On certain occasions, only some individuals show the expected response to a stressful event, while others are obviously unconcerned. "What is beginning to show," she said, "is that there are important differences in individual responses that may reflect social skills and temperament and which may have an impact on individual success and reproductive success." Return to July 10, 2000 contents page