Why are lemurs in the class mammalia? other than because they have hair?

Agene editing technology called crispr-cas9 uses cellular machinery to change the cell's genetic material. how might this technology be useful in treating diseases like cancer?

How do all types of diffusion/passive transport actually ‘work’ without using even the smallest amount of cellular energy?

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?