Article: In the wake of the racially-motivated" church shooting in Charleston, South Carolina, Yale was under criticism again in the summer of 2015 for Calhoun College, one of 12 residential colleges, which was named after John C. Calhoun, a slave-owner and strong slavery supporter in the nineteenth century. In July 2015 students signed a petition calling for the name change. They argued in the petition that—while Calhoun was respected in the 19th century as an "extraordinary American statesman"—he was "one of the most prolific defenders of slavery and white supremacy" in the history of the United States. In August 2015 Yale President Peter Salovey addressed the Freshman Class of 2019 in which he responded to the racial tensions but explained why the college would not be renamed. He described Calhoun as a "a notable political theorist, a vice president to two different U.S. presidents, a secretary of war and of state, and a congressman and senator representing South Carolina." He acknowledged that Calhoun also "believed that the highest forms of civilization depend on involuntary servitude. Not only that, but he also believed that the races he thought to be inferior, black people in particular, ought to be subjected to it for the sake of their own best interests." Racial tensions increased in the fall of 2015 centering on comments by Nicholas A. Christakis and his wife Erika regarding freedom of speech. In April 2016 Salovey announced that "despite decades of vigorous alumni and student protests," Calhoun's name will remain on the Yale residential college explaining that it is preferable for Yale students to live in Calhoun's "shadow" so they will be "better prepared to rise to the challenges of the present and the future." He claimed that if they removed Calhoun's name, it would "obscure" his "legacy of slavery rather than addressing it." "Yale is part of that history" and "We cannot erase American history, but we can confront it, teach it and learn from it." One change that will be issued is the title of “master” for faculty members who serve as residential college leaders will be renamed to “head of college” due to its connotation of slavery.

Question: Whose comments increased racial tension in the Fall of 2015?
Nicholas A. Christakis and his wife Erika