Ear­li­er this week, Har­ry Ostr­er wrote about a series of sci­en­tists who con­tributed to our con­tem­po­rary under­stand­ing of Jew­ish­ness. He will be blog­ging here all week for Jew­ish Book Coun­cil and MyJew­ish­Learn­ing.

If being Jew­ish were in the blood, then what bet­ter way to find the mark­ers of Jew­ish­ness then by study­ing blood itself? In his 1977 book The Genet­ics of the Jews, Arthur Mourant, one of the fore­most cat­a­loguers of blood groups dur­ing the 20th cen­tu­ry, explained the advan­tages to this approach, ​“In pop­u­lar anthro­pol­o­gy since time immemorial…the vis­i­ble and phys­i­cal­ly mea­sur­able body char­ac­ter­is­tics pre­ced­ed the hered­i­tary blood char­ac­ter­is­tics as the prin­ci­pal human tax­o­nom­ic mark­ers. Because of the pre­cise­ly known mode of inher­i­tance of blood char­ac­ters, the lat­ter have now super­seded them… The hered­i­tary dis­eases are, in gen­er­al, too rare to be of val­ue in stud­ies of lim­it­ed pop­u­la­tion sam­ples…” So mea­sur­ing blood groups is more pre­cise than mea­sur­ing heads and eas­i­er than iden­ti­fy­ing rare genet­ic dis­eases.

Mourant’s jour­ney to Jew­ish pop­u­la­tion genet­ics was long. As an Oxford-trained geol­o­gist, he joined the Geo­log­i­cal Sur­vey of Great Britain dur­ing the 1920s to cat­a­log the coal deposits in Lan­cashire. Unable to obtain an aca­d­e­m­ic post in geol­o­gy in Depres­sion-era Britain, he returned to his native island of Jer­sey and set up a lab­o­ra­to­ry offer­ing med­ical tests. But run­ning that lab­o­ra­to­ry was not sat­is­fy­ing, so in 1939, he entered St. Bartholomew’s Med­ical Col­lege in Lon­don. Upon his grad­u­a­tion with a med­ical degree in 1943, he became a Med­ical Offi­cer in the Nation­al Blood Trans­fu­sion Ser­vice. The demand for blood prod­ucts was great dur­ing the war and Mourant became a leader in the field. After the war, he direct­ed the UK Med­ical Research Council’s new­ly estab­lished Blood Group Ref­er­ence Lab­o­ra­to­ry, the inter­na­tion­al stan­dard for the World Health Organization.

A blood group is deter­mined by the pres­ence or absence of cer­tain sug­ars, pro­teins, or fats on the sur­faces of blood cells and oth­er types of cells. Dif­fer­ences in blood groups lim­it the pos­si­bil­i­ties for blood trans­fu­sions — blood can be trans­fused only for a com­pat­i­ble type. Trans­fu­sions among indi­vid­u­als of non­com­pat­i­ble types result in trans­fu­sion reac­tions in which anti­bod­ies in the recipient’s blood break down the trans­fused red cells.

The pres­ence of these anti­bod­ies was rec­og­nized first in 1901 by Karl Land­stein­er, a Vien­nese pathol­o­gist. As he not­ed lat­er in his Nobel Prize lec­ture of 1930, ​“My exper­i­ment con­sist­ed of caus­ing the blood serum and ery­thro­cytes (red blood cells) of dif­fer­ent human sub­jects to react with one anoth­er. The result was only to some extent as expect­ed. With many sam­ples there was no per­cep­ti­ble alter­ation, in oth­er words the result was exact­ly the same as if the blood cells had been mixed with their own serum, but fre­quent­ly a phe­nom­e­non known as agglu­ti­na­tion — in which the serum caus­es the cells of the alien indi­vid­ual to group into clus­ters – occurred.” Fol­low­ing Landsteiner’s lead, serum banks were cre­at­ed that col­lect­ed serum from indi­vid­u­als of known blood groups and used these sera to test new indi­vid­u­als to deter­mine their types. It was just such a lab­o­ra­to­ry that Mourant head­ed after the Sec­ond World War.

In the ABO sys­tem, there are four genet­i­cal­ly encod­ed blood groups: A, B, AB, and O — O rep­re­sents the absence of A or B. Peo­ple with the O group are also known as ​“uni­ver­sal donors,” because they can give blood to any­one. The study of ABO blood groups made it imme­di­ate­ly clear that there are dif­fer­ent fre­quen­cies among dif­fer­ent peo­ples. In Europe, the aver­age fre­quen­cy is 40 per­cent O, 40 per­cent A, 15 per­cent B, and 5 per­cent AB. In oth­er pop­u­la­tions, the bal­ance changes.

Mourant was among the first to appre­ci­ate the util­i­ty of using blood groups as pop­u­la­tion genet­ic mark­ers and the first to apply these to Jews. His cat­a­log had vary­ing data for the dif­fer­ent blood groups and for oth­er genet­ic mark­er sys­tems (includ­ing G6PD). He con­clud­ed that the blood group data cor­re­lat­ed with the known facts of Jew­ish his­to­ry – although pop­u­la­tion geneti­cists at the time and today would agree that it is hard to draw major con­clu­sions from a sin­gle genet­ic mark­er system.

The major Jew­ish com­mu­ni­ties were rel­a­tive­ly homo­ge­neous, yet dis­tinct from one anoth­er. Each of the com­mu­ni­ties bore some resem­blance to the local, non-Jew­ish pop­u­la­tion. In Mourant’s words, ​“Each major Jew­ish com­mu­ni­ty as a whole bears some resem­blance to indige­nous peo­ples of the region where it first devel­oped.” Recent stud­ies in Jew­ish pop­u­la­tion genet­ics have drawn upon analy­sis of the whole genome and have tend­ed to con­firm what Mourant observed – rel­a­tive homo­gene­ity with­in Jew­ish groups, dis­tinc­tive­ness between Jew­ish groups and some resem­blance with local, non-Jew­ish pop­u­la­tions. But Mourant was the first to study what was in the blood.

Dr. Har­ry Ostr­er is the author of Lega­cy: A Genet­ic His­to­ry of the Jew­ish Peo­ple. He is a med­ical geneti­cist who inves­ti­gates the genet­ic basis of com­mon and rare dis­or­ders. He is also known for his study, writ­ings, and lec­tures about the ori­gins of the Jew­ish peo­ple. He is a pro­fes­sor of Pathol­o­gy and Genet­ics at Albert Ein­stein Col­lege of Med­i­cine of Yeshi­va Uni­ver­si­ty and Direc­tor of Genet­ic and Genom­ic Test­ing at Mon­te­fiore Med­ical Cen­ter.