Sort the different barriers into their modes of reproductive isolation.
a snail with a flat disc-like shell
will not be able to mate with a
snail having a conical shell.
the reproductive organs of
male bush babies do not
match with the reproductive
organs of females of other
bush baby species
the mating call of a cricket is not
recognized by a cricket of other
species
the signals sent by a male firefly
are not recognized by the female
firefly of other species.
mechanical isolation
behavioral isolation
for

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?