Benefit 3 Greater Opportunities for Naturalistic Observations

The observational opportunities afforded by animal research are far greater than those available in human research. Relative to humans, animals can be observed for greater periods of time, in more detail, and in more contexts. These greater observational benefits are particularly true of captive animals, which can be closely monitored in some cases from conception until death. However, scientists can also observe wild animals living in natural habitats and collect voluminous behavioral and physiological data. Consequently, questions about how behavior and physiology change over time, across seasons, or in response to environmental triggers can be addressed. Equivalent opportunities for detailed and extensive naturalistic observations are rarer in human research. The relative ease with which naturalistic observations can be performed in animals means that more clues can be collected about the biological correlates and environmental factors that influence personality traits.

Research by Wingfield, Hegner, Dufty, and Ball (1990) in a variety of bird species illustrates the benefits of naturalistic observations of animals. These investigators recorded data on testosterone levels as well as aggressive and paternal behaviors in a wide variety of monogamous and polygynous bird species. Wingfield and colleagues proposed the "challenge hypothesis" to account for the relationship between testosterone levels and aggressive behavior in birds. The challenge hypothesis posits that fluctuations in testosterone levels during the breeding season are more closely related to aggressive behavior than to sexual behavior. Specifically, testosterone levels seem to rise as the mating season commences but peak during periods of intermale competition, suggesting that the increases in testosterone levels facilitate aggression. In addition, this theory suggests that testosterone only relates to aggression when there is competition over mates or territory. Thanks to Wingfield and colleagues' research in birds, the challenge hypothesis has been studied and validated in other animal species (e.g., male chimpanzees; Muller & Wrangham, 2004). Unfortunately, this hypothesis has been overwhelmingly overlooked by human researchers of testosterone and dominance (e.g., Mazur & Booth, 1998).

Other researchers have also profited from the naturalistic observational opportunities afforded by animal studies. By studying freely roaming baboons living in the Masai Mara National Reserve in Kenya, Virgin and Sapolsky (1997) uncovered links among testosterone levels, glucocorticoid levels, social status, and aggression. These researchers found that when the status hierarchy was stable, subordinate baboons had elevated glucocorticoid levels and suppressed testosterone levels, relative to dominant baboons. However, they also found individual differences in aggressive behavior and stress responses among subordinate baboons. The subordinate baboons that aggressed against other baboons after losing a fight had higher testosterone levels and lower glucocorticoid levels than did the ones that did not aggress after losing. This finding suggests that individual differences in aggression affect stress responses (Virgin & Sapolsky, 1997). These naturalistic observations shed light on the relationships between endocrinological patterns and individual differences in aggression. Moreover, the finding that displaced aggression is related to lower stress hormone levels suggests that social status and variations in aggression may have health implications for humans.

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