London (CNN) A recently hired adviser to British Prime Minister Boris Johnson has resigned, after backlash grew against his controversial past comments -- notably for claims that black Americans have lower IQs than white Americans and that compulsory contraception could prevent the creation of a "permanent underclass."

Andrew Sabisky, a self-described "superforecaster," announced his resignation as a "contractor" on Twitter Monday, saying that he did not want the "media hysteria about my old stuff online" to be a distraction for Johnson's government.

"I know this will disappoint a lot of ppl but I signed up to do real work, not be in the middle of a giant character assassination: if I can't do the work properly there's no point, & I have a lot of other things to do w/ my life," he said in another tweet.

Hey all,

The media hysteria about my old stuff online is mad but I wanted to help HMG not be a distraction. Accordingly I've decided to resign as a contractor. I hope no.10 hires more ppl w/ good geopolitical forecasting track records & that media learn to stop selective quoting — Andrew Sabisky (@AndrewSabisky) February 17, 2020

The 27-year-old was hired by Johnson's most senior adviser, Dominic Cummings, who advertised earlier this year for "weirdos and misfits with odd skills" to work alongside him.

Critics of the appointment singled out past comments made by Sabisky in support of eugenics and giving children mind-enhancing drugs for their educational benefits. "From a societal perspective the benefits of giving everyone modafinil once a week are probably worth a dead kid once a year," he said in a 2016 interview.

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