Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult organism, except notably among certain eusocial species (mostly haplodiploid insects). In humans, infertility may describe a woman who is unable to conceive as well as being unable to carry a pregnancy to full term. There are many biological and other causes of infertility, including some that medical intervention can treat. Infertility rates have increased by 4% since the 1980s, mostly from problems with fecundity due to an increase in age. About 40% of the issues involved with infertility are due to the man, another 40% due to the woman, and 20% result from complications with both partners. Women who are fertile experience a natural period of fertility before and during ovulation, and they are naturally infertile during the rest of the menstrual cycle. Fertility awareness methods are used to discern when these changes occur by tracking changes in cervical mucus or basal body temperature.