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Humans pressed 2 buttons for points that were exchangeable for money. Pressing 1 of the buttons, the impulsive choice, produced 2 points over 4 s. Pressing the other button, the self-controlled choice, produced 10 points over 4 s after a 16-s delay. Each point was exchangeable for 1 cent ($0.01). All subjects earned 1 cent ($0.01) for every 3 s they kept their right hand immersed in water. All subjects made 30 choices. In the experimental, pain, condition the water contained ice and was maintained at approximately 5 °C. In the control condition the water temperature averaged 33 °C. Subjects in the pain condition made fewer self-controlled responses, rated the water as more painful and more distracting, and kept their hands in the water for shorter durations than subjects in the control condition. The results have evolutionary and societal implications and suggest that variables affecting subjects' physiological state, or least their subjective physiological state, need to be taken into account for a complete understanding of human "self-control." Impulsiveness may be an evolutionary adaptation to aversive stimulation.