Variability hypothesis - Wikipedia

Toggle the table of contents Variability hypothesis 6 languages العربية Español فارسی 한국어 עברית Svenska Edit links Article Talk English Read Edit View history Tools Tools move to sidebar hide Actions Read Edit View history General What links here Related changes Upload file Permanent link Page information Cite this page Get shortened URL Download QR code Print/export Download as PDF Printable version In other projects Wikidata item Appearance move to sidebar hide From Wikipedia, the free encyclopedia Hypothesis that human males have more variance in certain traits compared to females Two distribution curves with identical means but different variabilities. The curve with the greater variability (green) yields higher values in both the lowest and highest ends of the range. The variability hypothesis , also known as the greater male variability hypothesis , is the hypothesis that human males generally display greater variability in traits than human females do. It has often been discussed in relation to human cognitive ability , where some studies appear to show that males are more likely than females to have either very high or very low IQ test scores . In this context, there is controversy over whether such sex-based differences in the variability of intelligence exist, and if so, whether they are caused by genetic differences, environmental conditioning, or a mixture of both. Sex-differences in variability have been observed in many abilities and traits – including physical, psychological and genetic ones – across a wide range of sexually dimorphic species. On the genetic level, the greater phenotype variability in males is likely to be associated with human males being a heterogametic sex, while females are homogametic and thus are more likely to display averaged traits in their phenotype. [ 1 ] History [ edit ] The notion of greater male variability—at least in respect to physical characteristics—can be traced back to the writings of Charles Darwin . [ 2 ] When he expounded his theory of sexual selection in The Descent of Man and Selection in Relation to Sex , Darwin cites some observations made by his contemporaries. For example, he highlights findings from the Novara Expedition of 1861–1867 where "a vast number of measurements of various parts of the body in different races were made, and the men were found in almost every case to present a greater range of variation than the women" (p. 275). To Darwin, the evidence from the medical community at the time, which suggested a greater prevalence of physical abnormalities among men than women, was also indicative of men's greater physical variability. Although Darwin was curious about sex differences in variability throughout the animal kingdom, variability in humans was not a chief concern of his research. The first scholar to carry out a detailed empirical investigation on the question of human sex differences in variability in both physical and mental faculties, was the sexologist and eugenecist Havelock Ellis . In his 1894 publication Man and Woman: A Study of Human Secondary Sexual Characters , Ellis dedicated an entire chapter to the subject, entitled "The Variational Tendency of Men". [ 3 ] In this chapter he posits that "both the physical and mental characters of men show wider limits of variation than do the physical and mental characters of women" (p. 358). Ellis documents several studies that support this assertion (see pp. 360–367), and "By the 1890s several studies had been conducted to demonstrate that variability was indeed more characteristic of males...The biological evidence overwhelmingly favored males as the more variable sex." [ 4 ] Early controversies in the 20th century [ edit ] The publication of Ellis's Man and Woman led to an intellectual dispute about the variability hypothesis between Ellis and the statistician Karl Pearson , whose critique of Ellis's work was both theoretical and methodological. After Pearson dismissed Ellis's conclusions, he then "presented his own data to show that it was the female who was more variable than the male" [ 4 ] Ellis wrote a letter to Pearson thanking him for the criticisms which would allow him to present his arguments "more clearly & precisely than before", but did not yield his position regarding greater male variability. [ 4 ] Support for the greater male variability hypothesis grew during the early part of the 20th century. [ 2 ] During this period, the attention of researchers shifted towards studying variability in mental abilities partly due to the advent of standardised mental tests (see the history of the Intelligence quotient ), which made it possible to examine intelligence with greater objectivity and precision. One advocate of greater male variability during this time was the American psychologist Edward Thorndike , one of the leading exponents of mental testing who played an instrumental role in the development of today's Armed Services Vocationa...