Theorists and researchers who explain criminal behavior by reference to the offender's own biological, physiological or psychological makeup, beginning with the nineteenth century positivist school, which broke from the classical school's assumption of free rational choice to argue that criminality could be studied scientifically as a determined trait, and continuing through modern biosocial criminology, which studies how genetics, brain structure and other biological factors interact with the social environment to shape antisocial behavior. This group gathers the positivist school's own founders and their immediate critics and successors in criminal anthropology, along with contemporary biosocial researchers studying the neurobiology, genetics and psychology of offending, and it excludes researchers whose central claim is about the offender's social environment, economic position or life-course development rather than an individual biological or psychological trait, who belong instead under Chicago School and Social Disorganization Theory, Strain, Anomie and Subcultural Theory or Developmental and Life-Course Criminology.