Which of the following examples results from disruptive selection? a. the birth weight at which newborn humans are most likely to survive and the average weight of newborn humans are about the same. b. there is an increase in antibiotic-resistant strains of bacteria. c. there is an increase in the number of different breeds of dog. d. garter snakes with different coloration patterns behave differently when threatened.

Astudy by solloch and et. al., in 2017, gives the map above which shows the frequency of alleles with a ccr5-delta32 mutations over 87 different countries. this mutation deletes the presence of a co-receptor (ccr5) on the outside of human t-cells (lymphocytes). some viruses, such as the one responsible for the black death and human immunodeficiency virus (hiv), require this receptor for attachment to host cells during the infection process. the black death was an epidemic that passed over northern europe during the 14th century killing nearly 60% of europeans. according to this information, which explanation best explains why northern europeans show a greater immunity for hiv than some other parts of the world?