Explain the regional differences

Question: Gene frequencies for the ABO alleles vary geographically. For example the I^A allele makes up nearly 50% of the genes for blood type among Australian Aborigines, about 25% in Central Asian populations, and 0% in peoples native to South America. No blood type has sufficient selective advantage over another to explain these regional differences. From these facts, what can you infer about the history of our species? Did humanity develop as a large and continuos population spreading out across the planet, or did we disperse while still living in small scattered groups?

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