Sampson’s knees are tucked into his chest. Beneath muscular legs, nimble toes wrap around a branch no more than four inches in diameter. Several feet away, Ferdinand rests with a leg outstretched, drawing lazy circles through his bushy hair. The valley is silent, save for the soft, breathy pant grunts that Sampson emits between nervous glances at the group’s alpha. At nineteen years of age, Sampson is experiencing the dual-edged sword of excitement and insecurity that accompanies a male chimpanzee’s transition into early adulthood. Unlike his younger brother, Siri, Sampson no longer relies on the comfort of his mother’s company, and many of his days are spent traveling or foraging in isolation. Fostering a relationship with the alpha may be a crucial step towards Sampson’s successful integration into the social world of Gombe’s adult males. When the seasons change and groups begin to form, Ferdinand has the social power to intervene on behalf of the young up-and-comer in any squabbles that might befall him. Anxious to approach, Sampson’s pant grunts become deeper in sound and more rapid. Like an established older gentleman, Ferdinand looks over as if to communicate the much-relished Go ahead, kid, take a seat, and it is Sampson’s opportunity to make an impression.
Sampson saunters forward and perches on the branch beside the foremost male in the Kasekela community. Watching Sampson maneuver about the ectoparasite removal process, the primate version of “schmoozing” , is almost as painful as witnessing happy hour in a financial district. Sampson’s false bravado is so strikingly familiar that I begin picturing him in a necktie. His weight is centered with a steady grip but despite his best efforts to appear nonchalant, his quivering fingers are a tell, and it’s obvious that the young male’s interest in ascending the social hierarchy may be more difficult than he had originally imagined. Before Sampson has a chance to settle in next to the alpha, a sound is heard from below. Both males peer forward to see who approaches, and slowly a figure emerges from the brush. It is Eliza, a young female carrying a new infant, who quickly climbs up to the males with her own set of pant grunts, though they are meant mostly for Ferdinand. As Sampson’s spotlight moment is infringed upon by another chimp (a non-conceptive female, no less!) his muddled state of insecurity and agitation gets the better of him. Eliza takes one step too close, and Sampson lashes out.
Given the circumstances, this outburst, in addition to being uncalled for, is risky. Sampson has attacked a group mate in the presence of the alpha, an action that Ferdinand is liable to rebuke with his own set of force. As an observer, it is easy to roll one’s eyes at Sampson’s impulsive behavior, and attribute his lack of foresight to the unattractive avarice of a would-be social climber. But Sampson’s hazardous decision making process poses an interesting question: why didn’t he just play it cool?
While we cannot rule out the possibility that Eliza recently scoffed at one of Sampson’s pick up lines, it seems more likely that Sampson’s impetuous behavior is liked to other aspects of his biology. One of the more compelling explanations may relate to the steroid hormone testosterone and its reported effects on emotions and risk preferences. Testosterone plays an important role in the mediation of aggressive behavior, mating, and dominance negotiation: males maintain minimal levels testosterone to facilitate sexual behaviors, and experience spikes when they face competitive disputes. Elevated levels of testosterone can prompt aggression, and facilitate successful outcomes in competitive situations . Evidence also suggests that when males walk away from contests as winners, testosterone levels are often elevated, which in turn can facilitate winning again in the future. In a sense, the perceived challenge that increases testosterone, that stimulates aggression, that facilitates winning (stick with me here), that further increases testosterone and risk-prone behavior, that stimulates further aggression, may create a feedback loop from which young risers like Sampson find it difficult to break [See 3 for a graphical representation of this run-on sentence]. But for a newly adult male looking to roll his way up the dominance hierarchy, this type of feedback loop may serve an advantage. And nowhere are the profits of testosterone and risk-prone behavior more apparent than (you guessed it!) happy hour in a financial district.
The trading floor of a London investment firm provides one of the most convincing examples of the relationship between testosterone and its competitive payouts . In one study, researchers set up shop on a mid-sized trading floor, requesting saliva samples from professional traders as they made large exchanges (between £100,000 and £500,000,000!) at high frequencies, principally in German interest rate futures. “At 11:00 AM and 4:00 PM, subjects deposited 3 ml of saliva into a polystyrene vial,”  a.k.a., the nice business men took turns spitting into plastic tubes before lunch and dinner. Results demonstrated that on days when traders had elevated morning testosterone, afternoon profits were significantly higher than on days of low morning testosterone. This pattern was particularly pronounced in traders who had more than two years of experience, implying that testosterone may actually be a performance enhancer when operating at moderate levels . But just like any hormone, moderation is the key to optimal functioning, as the over-production of testosterone can have deleterious effects on what is arguably the most important tool at a trader’s disposal: the brain. Specifically, if testosterone remains at elevated levels as opposed to adaptive, respond-and-release peaks, it can over-activate areas of the brain involved in economic decision-making and rational choice . Being up to one’s eyeballs in testosterone, while great for chest-beating, cat-calling, and tossing back Jägerbombs, can actually interrupt the neural systems required to generate logical thought.
Now before you run off to demand a spit sample from your portfolio manager, allow me to tie this all together. Sampson, not unlike a young trader eager to make his stake in the world, is stuck in the difficult balancing act of maintaining a competitive edge without being… well… too much of a jerk. Flying off the handle is never a desirable quality in human or chimpanzee, but it may be the unfortunate tradeoff of a neuroendocrine process that helps young males in other ways, like rising to the social demands of adulthood. Luckily for Sampson, his little tantrum was a much needed sample in my dissertation data, so his bad behavior is forgiven. Unluckily for humans, we have the cognitive capacity to discern correlation from causation, and thus excuses such as But my chronically elevated levels of endogenous testosterone made me do it! do not suffice when trying to explain bar fights, and other hormone-related mishaps.
 Dunbar, R. I. 1991. Functional significance of social grooming in primates. Folia primatologica, 57, 121-131.
 Wingfield, J. C., Hegner, R. E., Dufty, A. M. & Ball, G. F. 1990. The ‘challenge hypothesis’: theoretical implications for patterns of testosterone secretion, mating systems, and breeding strategies. American Naturalist, 136, 829–846.
 Coates, J. M., Gurnell, M. & Sarnyai, Z. 2010. From molecule to market: steroid hormones and financial risk-taking. Philosophical Transactions of the Royal Society of Britain, 365, 331–343.
 Coates, J. M. & Herbert, J. 2008. Endogenous steroids and financial risk taking on a London trading floor. Proceedings of the National Academy of Science, USA, 105, 6167–6172.