to Arthur Jensen's 1969 article, "How Much Can We Boost IQ and Academic Achievement?" Paternal age effect on DNA Crow also did research and writing in how DNA in sperm degrades as men age, through repeated copying, and can then be passed along to children in permanently degraded form, which they likely then pass on as well. As a result, he said in 1997 that the "greatest mutational health hazard to the human genome is fertile older males". He described mutations that have a direct visible effect on the child's health and also mutations that can be latent or have minor visible effects on the child's health; many such mutations allow the child to reproduce, but cause more serious problems for grandchildren, great-grandchildren and later generations A 2009 review prematurely concluded that the absolute risk from paternal age for genetic anomalies in offspring was low, and stated that "there is no clear association between adverse health outcome and paternal age but longitudinal studies are needed." However, newer studies supported Crow's claims. A study in 2006 of 132,000 Israeli adolescents discovered men in their 30s are 1.6 times as likely to have a child with autism as men under 30, with men in their 40s having a sixfold increase in risk Further studies in Sweden (2.6 million children), Denmark (2.98 million), and an international dataset of 5.7 million children showed a definite link between increased paternal age and autism risk. A widely-referenced Icelandic whole-genome sequencing effort led by Kári Stefánsson of DEcode Genetics and published in Nature also concluded similarly. Research Much of Crow’s research was in the area of theoretical population genetics, but he has often ventured into the laboratory. Over a career that spanned more than 50 years, Crow and his collaborators studied a variety of traits in Drosophila, dissected the genetics of DDT resistance, measured the effects of minor mutations on the overall fitness of populations, described the behavior of mutations that do not play the selection game by Darwin’s rules, and investigated many other subjects. His theoretical work has touched virtually every important subject in population genetics. Crow developed the concept of genetic load, has contributed to the theory of random drift in small populations, has studied the effects of non-random mating and age-structured populations, and has considered the question, “What good is sex?” He also developed ways to estimate inbreeding in human populations by making use