“If race is a cultural category, why can’t you choose your identity?” my students asked over dinner last Wednesday. They were thinking through the news from Spokane, where it was revealed that the president of the NAACP did not have African American heritage.

Then, the next morning, we woke up to the news that a white man shot nine people at Emanuel AME Church in Charleston. For the people who died because this man hated and feared black people, race was clearly not a flexible identity, something you can choose to wear or not depending on how well it fits.

This juxtaposition, of a minor scandal and a major act of racially motivated terrorism, makes me ask myself what science can teach us about our country’s long history and present reality of racism. Here are three examples that help me think about race.

Race is a poor category for understanding the genetic variation within our species. Human populations mix constantly, and genes quickly jump over the social boundaries we create of ethnicity and race. Very few individuals in a diverse country like ours have genes from only one ancestral group. Yet the study of patterns of ancestry within the genome can still be useful, showing us the ways that our social categories have shaped that mixing. For example, the frequent presence of genes that mark European ancestry in the genomes of the descendants of enslaved Africans points to the widespread practice of rape of black women by the white men who owned them.

Another use of DNA, to establish the identity of perpetrators in crimes, underscores the terrible power of the white supremacist myth that black men are “raping our women.” Of the first 250 convictions overturned by DNA evidence in the United States, 70% involved a black or Latino defendant. 89% of the wrongful convictions involved sex crimes, which is striking when you consider that only 10% of all prisoners have been convicted of sexual offenses. This myth is not just deadly when it motivates dangerous vigilantes to carry out modern day lynchings. It permeates our criminal justice system, and frequently condemns innocent men to death or to long years in prison.

The researchers at Project Implicit and other neuroscientists have developed tools for revealing the hidden biases that are outside our conscious control.  Despite our best intentions, most white people’s brains easily connect a black face with something negative. Our response time lags when we try to put that same face together with a positive word. This does not mean that we are all doomed to be racists forever. Once we acknowledge the power these social categories have over us, we can start working to change them. We can intentionally expose ourselves to positive images of people who are different from us. This week, I have been reading the short biographies in the news of the nine remarkable people we lost in Charleston. I hope their courage will teach my brain a few things about love.