In 2011 and 2012 scientists working on the banana river in florida recorded a dramatic increase in the number of manatee deaths over the past 50 years this are has also seen the human population increase by more that 500000 people it is beloved that the pollution from numerous sewage tanks leaked into the water eliminating the manatees food source replacing it with an alfa that is toxic to the manatee this is an example of

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?