When given a choice between steady rewards and the chance for more, monkeys will gamble, a new study found. And they’ll keep taking risks as the stakes rise and dry spells get longer. The research, in which scientists also pinpointed brain activity during the gambling, could provide insight into the human penchant for risk. In humans, it’s thought that low levels of the neurotransmitter serotonin might make one more risk-prone and impulsive. Perhaps, the scientists say, future work will shed light on the source of pathological gambling, obsessive-compulsive disorder and even depression.