Monkeys and apes, like humans, mate in all months of the year instead of in a rutting season. Unlike humans, however, female apes experience unusually strong sexual desire for a few days shortly before and during the oestrus periods, and have intensive sexual relations at that time. The males are attracted to the females by their scent or by brightly colored swellings in the sexual region
. Oestrus-mating appears to be especially pronounced in primate species more remote from humans. The apes and some monkeys carry on less intensive, monthround sexuality in addiction (addition)
to oestrus-mating, approaching human patterns more closely. In humans, sexual desires and relations are regulated less by hormonal changes and more by mental images, emotions,cultural rules and individual preferences.
According to the passage
, primates' sexual activities are carried_____.
a. less by the demand of females than by that of males
b. more by physical desire than by nonphysical factors
c. more frequently than human beings'
d. less frequently than human beings'