who has coined the concept of in group and out group
Ingroups and outgroups The terminology was made popular by Henri Tajfel and colleagues during his work in formulating social identity theory. The significance of ingroup and outgroup categorization was identified using a method called the minimal group paradigm. Tajfel and colleagues found that people can form self-preferencing ingroups within a matter of minutes and that such groups can form even on the basis of seemingly trivial characteristics, such as preferences for certain paintings.[1][2][3][4][5]
ABO blood group system It was subsequently found that the Czech serologist Jan Janský had independently pioneered the classification of human blood into four groups in 1907,[8] but Landsteiner's independent discovery had been accepted by the scientific world while Janský remained then in relative obscurity. However, in 1921 an American medical commission acknowledged Janský's classification. Jan Janský is nowadays credited with the first classification of blood into the four types (I, II, III, IV).