S. dumicola. (Credit: Bernard DUPONT via Wikimedia Commons)
Spiders have helped scientists debunk the Great Man Theory, a 19th-century notion positing that highly influential individuals use their power—be it personal charisma, intelligence, wisdom, or political skill—to maximize their impact in shaping the course of history.
“We wanted to see whether the presence of these particularly bold individuals changed how a society behaves collectively…”
Working with the African social spiders Stegodyphus dumicola in their native habitats, evolutionary ecologist Jonathan Pruitt created a model for exploring leadership dynamics and social susceptibility—the tendency of individuals to change their behavior in response to interactions with influential group members.
Pruitt found that the social susceptibility of the population majority—and not the influence of key individuals—is what drives leadership. The results appear in the journal Current Biology.
“We knew from previous studies that in a social group, the rare presence of bold individuals—who constitute between 1 and 5 percent of a population—radically changes collective behavior,” says Pruitt, an associate professor in the University of California, Santa Barbara’s department of ecology, evolution, and marine biology.
“This new research evaluates whether the rise and fall of societies could be contingent on having just one or a few of these key individuals and whether the profitability of their presence might change based on the environment.”
Researchers hand-painted Stegodyphus dumicola to keep track of individuals. (Credit: Jonathan Pruitt/UCSB)
Pruitt and his team set up 240 experimental societies across two different precipitation gradients in Africa: one in the Namib Desert heading north to Angola and a second from the Kalahari Desert heading east to Lesotho. Some of these colonies contained particularly bold spiders (putative leaders) and some did not. The researchers then monitored these colonies’ behavior and survival for the next six months.
The scientists determined the boldness of individual spiders by exposing them to a directional jet of air. Because S. dumicola cannot see well, they interpret air movement as a predator such as a bird, bat, or wasp. They respond with a death-feigning posture wherein they tuck their legs and huddle into a ball. Bold individuals don’t hide for long, but shy ones can take 20 minutes to an hour to recover.
“We wanted to see whether the presence of these particularly bold individuals changed how a society behaves collectively, and whether the aggressiveness of a society determined the likelihood of its members surviving or dying together in a sudden extinction event,” Pruitt explains.
“We found no association between how a society behaved and whether it lived or died at wet sites; nor did bold individuals have a large effect on colony behavior at these sites. However, we found a very tight association between the presence of bold individuals and societal aggressiveness at arid sites, and colonies containing bold individuals were far more likely to survive in these habitats.”
The fact that the same rare personality types existed at both dry and wet sites, but varied in their degree of apparent social influence across these habitats, allowed the investigators to decipher, for the first time, whether it is the traits of the leaders or the social context in which they reside that truly drives their influence.
As it turned out, the population majority determined whether these key group members could emerge at all, thus debunking the Great Man Theory and its parallel hypotheses regarding “keystone individuals” in a variety of animal societies. Instead, social influence appears to emerge from shy, generic spiders.