Early studies by Luigi Cavalli-Sforza used polymorphisms from proteins found within human blood (such as the ABO blood groups, Rhesus blood antigens, HLA loci, immunoglobulins, G6PD isoenzymes, amongst others).[1] One of the lasting proposals of this study with regards to Europe is that within most of the continent the majority of genetic diversity may best be explained by immigration coming from the southeast towards the northwest or in other words from the Middle East towards Britain and Ireland. Cavalli-Sforza proposed at the time that the invention of agriculture might be the best explanation for this.