INTRODUCTION

The door to the study of genetically based variation in humans cracked open at the beginning of the twentieth century with the discovery by Landsteiner (1901) of ABO blood group substances whose Mendelian mode of inheritance was later established by Bernstein (1924). Needless to say, an early trickling of discoveries has led to a flood over the past century of new and important revelations concerning the nature and significance of human genetic variation. This chapter will cover approximately three-fourths of that history as it unfolded via the discovery and elucidation of a host of markers. A helpful review of genetic markers known as of the early 1970s and their role in the study of human evolution can be found in Crawford (1973). Another recent review of classic markers and their contribution toward understanding North American Native genetic variation appeared in O'Rourke (2006). Two current textbooks that provide substantial coverage of traditional markers, along with DNA markers and other topics relevant to human biological variation, are Mielke et al. (2006) and Molnar (2006).

Over the years markers have come to mean fairly consistently defined hereditary units. An early reference to the use of the term is found in Race and Sanger (1962) who discuss markers, in their case human blood groups, as characters that help to locate genes on chromosomes. This was, of course, early in any attempts to construct physical gene maps. Sometime later, genetic markers were associated with specific polymorphic loci that defined particular segments of chromosomes (Cavalli-Sforza et al.,1994).