Why is the adaptation in the previous question an advantage in hot, dry climates? (Think about photosynthesis, sun exposure, transpiration rate...) Answers:
A. Small leaves are less susceptible to water loss through evaporation, but photosynthetic rate can improve by increasing leaf density.
B. Large leaves hold on to large amounts of water and the weight of the plant will be too great for small plants to withstand.
C. Small leaves prevent animals from nesting in the plant structure preventing plants from being eaten.

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?