An adviser to Boris Johnson quit the British Government a few days into the job after amid controversy over his claims that white Americans are more intelligent than their black compatriots.
Andrew Sabisky, who was hired to work in Johnson's Downing Street office last week, said he had joined the government to do "real work" but found himself "in the middle of a giant character assassination."
"The media hysteria about my old stuff online is mad but I wanted to help HMG (Her Majesty's Government) not be a distraction," Sabisky wrote on Twitter. "Accordingly I've decided to resign as a contractor."
A spokeswoman for the prime minister's office confirmed that Sabisky had resigned but declined to comment further.
Sabisky became the focus of intense criticism today, with calls for Johnson to fire him. The row came after a posting on an academic blog in 2014 came to light, in which he said: "You will see a far greater percentage of blacks than whites in the range of IQs 75 or below, at which point we are close to the typical boundary for mild mental retardation."