it is true that those with lower IQ and less education are producing more offspring, then they are fitter than those of higher IQ and more education". According to Mackintosh, eugenicist arguments are not based on a "biological imperative, but rather on a particular set of value judgements". In Eugenics: A Reassessment (2001), Lynn claimed that embryo selection as a form of standard reproductive therapy would raise the average intelligence of the population by 15 IQ points in a single generation (p. 300). If couples produce a hundred embryos, he argues, the range in potential IQ would be around 15 points above and below the parents' IQ. Lynn argues that this gain could be repeated each generation, eventually stabilising the population's IQ at a theoretical maximum of around 200 after as little as six or seven generations. Race and national differences in intelligence In the late 1970s, Lynn wrote that he found the average IQ of the Japanese to be 106.6, and that of Chinese people living in Singapore to be 110. Lynn's psychometric studies were cited in the 1994 book The Bell Curve and were criticised as part of the controversy surrounding that book. In his 2002 article, "Skin color and intelligence in African Americans", published in 2002 in Population and Environment, Lynn concluded that lightness of skin color in African Americans is positively correlated with IQ, which he claims derives from the higher proportion of Caucasian admixture. However, Lynn failed to control for childhood environmental factors that are related to intelligence, and his research was criticised by a subsequent article published in the journal by Mark E. Hill. The article concluded that "...[Lynn's] bivariate association disappears once childhood environmental factors are considered". In his response to Hill, Lynn wrote that "The conclusion that there is a true association between skin color and IQ is consistent with the hypothesis that genetic factors are partly responsible for the black–white difference in intelligence… the evidence that a statistically significant correlation is present confirms the genetic hypothesis". This statement was described by Marcus Feldman as "nonsensical". In 2010 Earl B. Hunt summarized Lynn's research in this area along with that of Tatu Vanhanen, that he is "highly critical of their empirical work, and even more so of their interpretations," but that they "do deserve credit for raising important questions in a way that has resulted in interesting and important findings." Lynn proposed