“tribe. Several studies”: McCutcheon, R., Bloomfield, M., Dahoun, T.,…& Howes, O., “Amygdala Reactivity in Ethnic Minorities and Its Relationship to the Social Environment: An fMRI Study,” Psychological Medicine 48, no. 12 (2018), and Hart, A. J., Whalen, P. J., Shin, L. M., McInerney, S. C., Fischer, H., & Rauch, S. L., “Differential Response in the Human Amygdala to Racial Outgroup vs Ingroup Face Stimuli,” Neuroreport 11, no. 11 (August 2000): 2351–55.

“preparation for a fight”: Javanbakht, A., & Saab, L., “The Science of Fright: Why We Love to Be Scared,” The Conversation, October 26, 2017, https://theconversation.com/the-science-of-fright-why-we-love-to-be-scared-85885?xid=PS_smithsonian.

“sex as they get older”: Telzer, E. H., Flannery, J., Humphreys, K. L., Goff, B., Gabard-Durman, L., Gee, D. G., & Tottenham, N., “The Cooties Effect: Amygdala Reactivity to Opposite- Versus Same-sex Faces Declines from Childhood to Adolescence,” Journal of Cognitive Neuroscience 27, no. 9 (April 7, 2015): 1685–96.

“exhibits less empathy”: Meyer, M. L., Masten, C. L., Ma, Y., Wang, C., Shi, Z., Eisenberger, N. I., & Han, S., “Empathy for the Social Suffering of Friends and Strangers Recruits Distinct Patterns of Brain Activation,” Social Cognitive and Affective Neuroscience 8, no. 4 (2013): 446–54.

“outside our own”: Cikara, M., Bruneau, E., & Saxe, R., “Us and Them: Intergroup Failures of Empathy,” Current Directions in Psychological Science 20, no. 3 (2017): 149–53.

“rival sports teams”: Hein, G., Silani, G., Preuschoff, K., Batson, C. D., & Singer, T., “Neural Responses to Ingroup and Outgroup Members’ Suffering Predict Individual Differences in Costly Helping,” Neuron 68, no. 1 (October 2010): 149.

“were of their same race”: Avenanti, A., Sirigu, A., & Aglioti, S. M., “Racial Bias Reduces Empathic Sensorimotor Resonance with Other-Race Pain,” Current Biology 20, no. 11 (June 2010): 1018–22, and Xu, X., Zuo, X., Wang, X., & Han, S., “Do You Feel My Pain? Racial Group Membership Modulates Empathic Neural Responses,” Journal of Neuroscience 29, no. 26 (2009): 8525–29.

“more like schadenfreude”: Molenberghs, P., “The Neuroscience of In-Group Bias,” Neuroscience and Biobehavioral Reviews 37, no. 8 (September 2013): 1530–36.

“an overflowing toilet”: Harris, L. T., & Fiske, S. T., “Dehumanizing the Lowest of the Low: Neuroimaging Responses to Extreme Out-Groups,” Psychological Science 17, no. 10 (October 2006): 847–53.

“their same unique trait”: Nelson, L. J., & Miller, D. T., “The Distinctiveness Effect in Social Categorization: You Are What Makes You Unusual,” Psychological Science 6, no. 4 (1995): 246–49.

“In a 2002 article”: Fiske, S. T., “What We Know Now About Bias and Intergroup Conflict, the Problem of the Century,” Current Directions in Psychological Science 11, no. 4 (August 2002): 123–28.

“seem fair-minded”: Molenberghs, P., “The Neuroscience of In-Group Bias,” Neuroscience and Biobehavioral Reviews 37, no. 8 (September 2013): 1530–36.

“wrote in 2016”: The Conversation, Gelfand, M., Jackson, J. C., Harrington, J. R., “Trump Culture: Threat, Fear and the Tightening of the American Mind,” Scientific American, April 27, 2016, https://www.scientificamerican.com/article/trump-culture-threat-fear-and-the-tightening-of-the-american-mind/#.

“support for Trump”: Lopez, G., “The Past Year of Research Has Made It Very Clear: Trump Won Because of Racial Resentment,” Vox, December 15, 2017, https://www.vox.com/identities/2017/12/15/16781222/trump-racism-economic-anxiety-study.

“The Atlantic in 2018”: Khazan, O., “People Voted for Trump Because They Were Anxious, Not Poor,” Atlantic, April 23, 2018, https://www.theatlantic.com/science/archive/2018/04/existential-anxiety-not-poverty-motivates-trump-support/558674/.

“Wall Street Journal analysis”: Adamy, J., & Overberg, P., “Counties That Experienced Rapid Diversification Voted Heavily for Donald Trump,” Wall Street Journal, November 9, 2016, https://www.wsj.com/articles/counties-that-experienced-rapid-diversification-voted-heavily-for-donald-trump-1478741076.