Discussions of race and intelligence – specifically, claims of differences in intelligence along racial lines – have appeared in both popular science and academic research since the modern concept of race was first introduced. With the inception of IQ testing in the early 20th century, differences in average test performance between racial groups were observed, though these differences have fluctuated and in many cases steadily decreased over time. Further complicating the issue, modern science has shown race to be a social construct rather than a biological reality, and intelligence has no undisputed definition. The validity of IQ testing as a metric for human intelligence is itself disputed. Today, the scientific consensus is that genetics does not explain differences in IQ test performance between groups, and that observed differences are environmental in origin. Pseudoscientific claims of inherent differences in intelligence between races have played a central role in the history of scientific racism. The first tests showing differences in IQ scores between different population groups in the United States were the tests of United States Army recruits in World War I. In the 1920s, groups of eugenics lobbyists argued that these results demonstrated that African Americans and certain immigrant groups were of inferior intellect to Anglo-Saxon white people, and that this was due to innate biological differences. In turn, they used such beliefs to justify policies of racial segregation. However, other studies soon appeared, contesting these conclusions and arguing instead that the Army tests had not adequately controlled for environmental factors, such as socioeconomic and educational inequality between black people and white people. Later observations of phenomena such as the Flynn effect and disparities in access to prenatal care also highlighted ways in which environmental factors affect group IQ differences. In recent decades, as understanding of human genetics has advanced, claims of inherent differences in intelligence between races have been broadly rejected by scientists on both theoretical and empirical grounds. History of the controversy Claims of differences in intelligence between races have been used to justify colonialism, slavery, racism, social Darwinism, and racial eugenics. Racial thinkers such as Arthur de Gobineau relied crucially on the assumption that black people were innately inferior to white people in developing their ideologies of white supremacy. Even Enlightenment thinkers such as Thomas Jefferson, a slave owner, believed black people to be innately inferior to white people in physique and intellect. At the same time, prominent