For the year from July 1, 2011, to June 30, 2012 (the latest year for which statistics are available), exactly 16 PhDs in the mathematical sciences were awarded to black/African-American women in the entire U.S. Evelyn Thomas, now a postdoctoral fellow at the University of Maryland, Baltimore County, is one of them. UMBC mathematician and novelist Manil Suri profiles her for SIAM News, with the aim of shedding light on challenges and opportunities she has encountered along her career path.
UMBC postdoc Evelyn Thomas hopes “to communicate to everyday people that if there are problems they see in their communities: HIV/AIDS, gun violence, racism, sexism, homophobia—anything—a solution does lie within mathematics.”
The first defining event in Evelyn Thomas’s career was 9/11, when she was a sophomore at Spelman College. She spent all morning with her friends, watching the grim events unfold on TV. Most professors cancelled classes or held discussions to address the emotional trauma of students. But Thomas’s set theory professor conducted his afternoon class as usual, without the slightest reference to the attacks. It felt so surreal that Thomas decided never again to let her love for mathematics cut her off from the real world like this. She began to envisage a research career in mathematics rooted in the humanistic field of sociology, which was her minor.
The second defining moment came in April 2004. Thomas was watching Oprah Winfrey interview the writer J.L. King, who announced that he was on the “down low.” This is the term used of African-American men who secretly engage in sex with other men, without telling their wives or girlfriends. Her friends were as shocked as she was. “What if a partner or spouse was having unprotected sex with a man? The level of deception would be amazing,” Thomas says. Back then, she decided to do something unusual about it—make it the topic of her Ph.D. thesis.
The idea of choosing one’s own thesis topic in mathematics is almost unheard of. Thomas’s quest eventually led her to enlist Katharine Gurski of Howard University as her adviser. Gurski suggested bringing in Kathleen Hoffman of UMBC as co-adviser. “Both had expertise in applied mathematics,” Thomas says, “but each offered a different perspective, adding to the substance of the work.” Thomas successfully defended her thesis, The Effect of Bisexual Males on the Spread of Incurable Sexually Transmitted Diseases, in April 2012.
Perhaps more than any other factor, Thomas attributes her success to her parents: “Both their families realized education was the great equalizer—my maternal grandmother even obtained a college degree in the 1940s.” It helped that Thomas grew up in a stable middle-class family in Washington, DC, and attended public schools in relatively affluent areas. Still, she recalls feeling odd as the only black girl from her grade level enrolled in most of her advanced math courses.
Spelman College, one of the HBCUs (historically black colleges and universities), changed that. Suddenly, she was surrounded by black women with similar backgrounds, freeing her from the distractions of race and gender. “I could no longer simply define myself as the ‘smart black girl’—I had to find my own identity.” The “outstanding” mentorship there was matched by high standards: “Women were expected to pursue graduate and professional degrees.” Black female role models (like Monica Stephens Cooley) on the mathematics faculty offered living proof of a waiting world of possibility. “I absolutely think if I had not gone to an HBCU for my undergraduate degree, I would not have earned a PhD,” Thomas says.
She continued to experience the benefits of HBCUs at Howard University. The mathematics department (under the leadership of Aziz Yakubu) was creating partnerships within mathematical biology, specifically with DIMACS (the Center for Discrete Mathematics and Theoretical Computer Science at Rutgers) and MCMSC (the Mathematical, Computational and Modeling Sciences Center at Arizona State). Under a DIMACS initiative to forge relations between American and African students, Thomas was selected to visit mathematical conferences in both Johannesburg and Cape Town. (She also went to one in Israel.) In addition, she participated in an REU at Arizona State run by Carlos Castillo-Chavez, which specifically targeted Hispanics and Latinos. “It gave me a different perspective: conducting research at a predominantly white institution under a program aimed at other minorities,” she says.
The HIV modeling talks at the Cape Town conference were particularly compelling to Thomas. For the first time, she saw the urgency of the problem: Some of the African researchers spoke movingly of relatives they’d personally lost to AIDS. “They weren’t just creating HIV models for the sake of doing cool math, but to really solve problems that impacted their families and communities.” Back at Howard, Thomas began studying a paper* written by a group of African mathematicians describing the effect of bisexuals on the dynamics of HIV/AIDS spread. The authors’ SI (susceptible–infectious) model contained a crucial simplification: Bisexuals appeared in it only as infected individuals. At the point of infection, a certain proportion of both heterosexual and homosexual men were assumed to “switch” into this infected bisexual category.
Thomas believed that this dynamic was at odds with human sexuality. In her thesis, she therefore modeled the interactions between four distinct groups: heterosexual, homosexual, and bisexual males, and heterosexual females (see diagram below). New analytic techniques were needed to investigate a system with so many parameters. One of Thomas’s novel ideas was to use reduced models in which the value of the epidemic equilibrium of one subpopulation could be entered as a forcing term acting on other subpopulations. She was able to characterize precise conditions under which HIV would permeate the full system. To this end, she mathematically established something that might have been only suspected so far: The bridge between heterosexual females and bisexual males (in particular the down-low population) was the key determining factor.
Effects of bisexuals on the spread of HIV/AIDS: A simplification in a model she studied led Evelyn Thomas to construct a model for her PhD thesis that included the four distinct populations shown here.
Issues related to homosexuality can evoke strong reactions, but Thomas has encountered generally positive responses to her work. “People are surprised that math could be applied to such a sociological and topical problem,” she says. “If I know I am speaking with someone who is homophobic, I try to avoid any confrontation and find common ground.” A related question is how she feels working on mathematics that might affect people’s lives. Given the sad state of LGBT rights in many countries, what if her results were used as a justification to persecute gay or bisexual people?
“If anything, the takeaway should be the consequences of oppressing people for being simply who they are innately. For countries like Uganda, Russia, or Nigeria, my study shows how their anti-gay policies can have a negative trickle-down effect on their heterosexual populations.”
Since arriving at UMBC for her postdoc, Thomas has started a new epidemiological project based on the rise of cholera in Haiti after the devastating earthquake of 2010. She is also exploring the addition of age structure to her down-low model, which would make it a more computationally intensive PDE investigation. Her goal is to continue working on projects with social engagement. “I hope to communicate to everyday people that if there are problems they see in their communities: HIV/AIDS, gun violence, racism, sexism, homophobia—anything—a solution does lie within mathematics.”
*Z. Mukandavire et al., Assessing the effects of homosexuals and bisexuals on the intrinsic dynamics of HIV/AIDS in heterosexual settings
, Mathematical and Computer Modelling, 49 (2009), 1869–1882.