Asked by: Suttiwit Sukpinit, Thailand
Most animals time their reproductive season so that young are born or hatch when there is more food available and the weather isn’t so harsh. There are exceptions, though. Most dog breeds go into heat twice a year and many rodents reproduce almost continuously through the year. In some primates, social factors are more important than food availability.
Female chimpanzees don’t advertise when they are fertile and have promiscuous sex, regardless. This is thought to reduce the rate of infanticide from unrelated males, by making it hard for them to be sure whether or not they are the father of any offspring and this may have been important in humans too.
Human sexual behaviour does vary subtly throughout the menstrual cycle, though. A 2007 study at the University of New Mexico found that lap dancers earned more money when they were fertile; perhaps because they were unconsciously acting sexier.