Through the analysis we realized that some of the private antigens were shared between very distant populations in the first place, but we were also able to type different subspecies and even species of the mouse, and it turned out that these subspecies had antigens that we could not distinguish. They were... they seemed to be identical. So by that time I was in Germany. In Germany there are in... well, yes in Germany and in Europe there are two different species of a mouse. One is called domesticus and the other musculus.. or musculus, and they have very distinct areas where they live. Across Europe, across Germany, down from the Baltic down to the Mediterranean Sea runs a line which the mice respect. On one... well, it's a line that's almost political because at that time it divided... it ran across Germany and separated Eastern and Western Germany, by chance, totally by chance, and on the one... so on the one side is the western form of the wild mice, on the other side is the eastern form. The line runs near Munich, which was not too far for us, so we could collect mice on both sides.  And it is a line, it's a hybrid zone which means that the mice that meet there can occasionally breed.  The western and the eastern mice didn't mind breeding together, but studies showed that the number of progeny of these mice is reduced, dramatically reduced, so that there is some barrier... reproductive barrier emerging between the two forms of mice, the Eastern and the Western. So they were evolving if they were not already two different species.

By comparing the Western and the Eastern H2 type, we found that the same type appears to be present... in the same alleles by this definition... present in both forms. Now as far as it's known, the species have separated from each other about one to two million years ago, so this indicated that unless they exchanged these genes, that the genes were separated for one and two million years, and yet they appeared to be very similar. So that was strange because on the one hand there was tremendous variability in the H2 antigens in the mice, a very high number of different alleles, and on the other hand some of the alleles appeared to be constant for a long period of time.