Testosterone: an introduction
Today I want to talk about testosterone. I had intended for this post to be a short one, but then I kept digging and digging and, well, it turns out that testosterone is a pretty interesting subject. What I’m going to do today is give a bit of a review on it, and talk about the effect that it has on personal decision-making. In the next post, I’ll relate testosterone to social decision-making.
Testosterone does a lot of things, and most of them seem to revolve around social status effects – although that simplification may end up making things more confusing. What testosterone does do is, over time, enhance muscle performance and redistribute immune resources to prepare for injury (remember my post on social status and healing?). Several things cause increased levels of testosterone, with competition and sex being foremost among them. This isn’t just physically aggressive competition, either; chess will give you bursts of testosterone. Historically, calorically stressed populations will see seasonal variations in testosterone levels when men need to suppress aggressive behaviors during child rearing, or get ready for fighting and healing from fighting for status and mates. But don’t think that testosterone directly will make an individual wildly aggressive. As Robert Sapolsky notes in The Trouble With Testosterone
Round up some male monkeys…number 3, for example, can pass his day throwing around his weight with numbers 4 and 5, ripping off their monkey chow, forcing them to relinquish the best spots to sit in, but, at the same time, remembering to deal with numbers 1 and 2 with shit-eating obsequiousness…Take that third monkey and inject him with testosterone. Inject a ton of it in him…And no surprise, when you check the behavioral data, it turns out that he will probably be participating in more aggressive actions than before…Is he now raining aggressive terror on any and all in the group, frothing in an androgenic glaze of indiscriminate violence? Not at all. He’s still judiciously kowtowing to numbers 1 and 2 but has become a total bastard to numbers 4 and 5.
Males in industrialized societies, however, don’t have any caloric needs causing them to suppress testosterone. In order to examine testosterone in a more ‘natural’ setting, Trumble et al. turned to ‘pathogenically stressed forager-horticulturalists of the Bolivia Amazon’ (ie, poor and hungry people of the Amazon) who do indeed have lower testosterone levels. These tribal people were brought together and organized into teams for a soccer tournament. They found that testosterone was higher after the game in all participants, whether they won or lost. But pay attention to this: the individuals who thought they performed better had larger increases in testosterone immediately following the game. An hour later? The difference disappeared.
It’s this type of effect of confidence that caused (Wright et al. 2012) to examine the effect of testosterone on group collaboration. They put pairs of female subjects in a room and gave them a visual task where they had to decide which of two sets of bars were brighter. When the subjects disagreed, they were allowed to discuss it and then one of the pair had to make a decision based on the joint beliefs. But some of those subjects were given testosterone injections! And the ones who were given testosterone were more likely to trust their own injections. Although this seems like a nice result, we don’t really know what is happening during the verbal discussion. Does the testosteroned subject just verbally browbeat the other subject? What’s going on there?
So testosterone may act to reinforce egocentric behavior. How about risk-taking? That’s a little more complicated. In a gambling game – with the subject only competing against themselves – (Stanton et al. 2011) showed that high risk taking in a gambling task is associated with high testosterone, but the same group later showed that (Stanton et al. 2011 ) there is actually a U-shaped curve. Subjects with intermediate levels of testosterone are actually risk-averse, while low and high levels are risk-neutral. This is an important point, and something to keep in mind; often we are not sampling the whole distribution of testosterone levels, and the simple ‘high’ versus ‘low’ dichotomy may be misleading.
So we have seen that testosterone probably goes up and down based on caloric resources and in the presence of competition and mates (or mating). We’ll conclude next time with a discussion of how testosterone affects sociality, and how things are even more complicated than high/low or U-shaped.
Trumble, B., Cummings, D., von Rueden, C., O’Connor, K., Smith, E., Gurven, M., & Kaplan, H. (2012). Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the ‘challenge hypothesis’ Proceedings of the Royal Society B: Biological Sciences, 279 (1739), 2907-2912 DOI: 10.1098/rspb.2012.0455
Wright, N., Bahrami, B., Johnson, E., Di Malta, G., Rees, G., Frith, C., & Dolan, R. (2012). Testosterone disrupts human collaboration by increasing egocentric choices Proceedings of the Royal Society B: Biological Sciences, 279 (1736), 2275-2280 DOI: 10.1098/rspb.2011.2523
Stanton, S., Liening, S., & Schultheiss, O. (2011). Testosterone is positively associated with risk taking in the Iowa Gambling Task Hormones and Behavior, 59 (2), 252-256 DOI: 10.1016/j.yhbeh.2010.12.003
Stanton, S., Mullette-Gillman, O., McLaurin, R., Kuhn, C., LaBar, K., Platt, M., & Huettel, S. (2011). Low- and High-Testosterone Individuals Exhibit Decreased Aversion to Economic Risk Psychological Science, 22 (4), 447-453 DOI: 10.1177/0956797611401752