What is an advantage of a degenerate genetic code?

mutations are more likely to alter proteins, increasing the rate of evolution.

mutations are less likely to alter protein sequence, decreasing the chances that a mutation will have deleterious consequences to the organism.

it increases the number of different proteins that can be coded by each gene.

it decreases the total number of trnas that have to be made.

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?