linked to earlier onset of sexual activity and increased short-term mating orientation. Daughters of absent fathers are more likely to seek short-term partners, and one theory explains this as a preference for outside (non-partner) social support because of the perceived uncertain future and uncertain availability of committing partners in a high-stress environment. Investment as predictor of mating strategies Concealed ovulation Women can only get pregnant while ovulating. Human ovulation is concealed, or not signaled externally. Concealed ovulation decreases paternity certainty because men are unsure when women ovulate. The evolution of concealed ovulation has been theorized to be a result of altriciality and increased need for paternal investment—if men are unsure of the time of ovulation, the best way to successfully reproduce would be to repeatedly mate with a woman throughout her cycle, which requires pair bonding, which in turn increases paternal investment. Mating orientations Sociosexuality was first described by Alfred Kinsey as a willingness to engage in casual and uncommitted sexual relationships. Sociosexual orientation describes sociosexuality on a scale from unrestricted to restricted. Individuals with an unrestricted sociosexual orientation have higher openness to sex in less committed relationships, and individuals with a restricted sociosexual orientation have lower openness to casual sexual relationships. However, today it is acknowledged that sociosexuality does not in reality exist on a one-dimensional scale. Individuals who are less open to casual relationships are not always seeking committed relationships, and individuals who are less interested in committed relationships are not always interested in casual relationships. Short- and long-term mating orientations are the modern descriptors of openness to uncommitted and committed relationships, respectively. Parental investment theory, as proposed by Trivers, argues that the sex with higher obligatory investment will be more selective in choosing sex partners, and the sex with lower obligatory investment will be less selective and more interested in "casual" mating opportunities. The more investing sex cannot reproduce as frequently, causing the less investing sex to compete for mating opportunities. In humans, women have higher obligatory investment (pregnancy and childbirth), than men (sperm production). Women are more likely to have higher long-term mating orientations, and men are more likely to have higher short-term mating orientations. Short- and long-term mating orientations influence women's preferences in men. Studies have found that women put great emphasis on career-orientation, ambition and devotion only when considering a long-term partner. When marriage is not involved, women put greater emphasis on physical attractiveness.