"Population growth results first and foremost from the physical labour that only the biological female can perform. This labour, which is performed by the woman’s body, can be described as reproductive labour and it includes the processes of menstruation, pregnancy, birth, and breastfeeding. These have been defined as natural processes or events, things that just happen, rather than as work performed by the woman, but like all other forms of labour these activities require energy and drain physical resources. The decline in levels of fertility that has taken place throughout much of the world has been decline in the level of this reproductive labour, but most scholars dismiss the notion that women had or have a particular motivation to reduce fertility. The pains and pleasures of the body are assumed to be perennial factors that are always present and therefore do not create change. However, changes in fertility rates show us that the burden of reproductive labour borne by the average woman has risen and fallen sharply over generations."