Andrew Sabisky – already under fire for attacking women’s sport and backing a risky mind-enhancing drug – also suggested more black people are “close to mental retardation”.
Downing Street refused to comment on the controversy provoked by the recruitment of Mr Sabisky, which followed Dominic Cummings’s call to sign up “misfits and weirdos”.
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But there were signs of a revolt by special advisers, some of whom said they would refuse to attend meetings with him, or respond to any requests he made.
And Jon Trickett, Labour’s Cabinet Office spokesman, said: “There are really no words to describe Boris Johnson’s appointment, as one of his senior advisers, of a man who is on record as supporting the forced sterilisation of people he considers not worthy.
“He must of course be removed from this position immediately.”
Calling himself a “super-forecaster”, he also said richer people are more intelligent, telling an interviewer: “Eugenics are about selecting ‘for’ good things.”
And he argued for giving all children modafinil, a drug that cuts the need for sleep by two-thirds, even at the cost of “a dead kid once a year”.
It has now emerged that Mr Sabisky wrote on Mr Cummings’s website in 2014: “One way to get around the problems of unplanned pregnancies creating a permanent underclass would be to legally enforce universal uptake of long-term contraception at the onset of puberty.
“Vaccination laws give it a precedent, I would argue.”
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In another blogpost, discussing female genital mutilation, he claimed: “It is still unclear to what extent FGM represents a serious risk to young girls, raised in the UK, of certain minority group origins. Much of the hue and cry looks more like a moral panic.”
And, also, in 2014, he said a higher rate of black Americans suffered from “intellectual disability” saying: “It [is] simply a consequence of the normal distribution of cognitive ability.”
No 10 has declined to say which policy area Mr Sabisky is working in, but confirmed he was a contractor working on specific projects.
Aged 27, he joined the administration following Mr Cummings’s rambling 3,000-word new year blogpost urging “misfits and weirdos” to help him transform government.
One source told The Times he had already made his mark, saying: “He dresses just like Dom in a scruffy jumper and jeans.
“He’s incredibly cocky and isn’t afraid of telling everyone what he thinks, however senior they are.”