Practice Paragraph 2
The Indian tribes of North and South America do not contain all the blood groups that are found in populations elsewhere. A fascinating glimpse into their ancestry is opened by this unexpected biological quirk. For the blood groups are inherited in such a way that, over a whole population, they provide some genetic record of the past. The total absence of blood group A from a population implies, with virtual certainty, that there was no blood group A in its ancestry; and similarly with blood group B. And this is in fact the state of affairs in America(Bronowski 92).
Bronowski, J. The Ascent of Man. Boston: Little Brown and Company, 1973