es and the presence of female sex hormones, which are a necessary prerequisite for reproduction. Thus, markers of high estrogen may reliably signal an immune system of such high quality that it can deal with the handicap of high estrogen. Also, there is evidence that estrogen's by-products are toxic in the body. Thus, markers of estrogen may honestly signal ability to cope with toxic metabolites. Sexual dimorphic traits in the human body can be found in the distribution of body fat (breast and buttocks), the general structure of the skeleton, that is bigger and more massive shoulders in males, and bigger pelvis in females, and finally muscle build. Male muscle build is probably the main differences. Again muscles are built up under the influence of male sex hormones, and muscles will be of use for males in male-male competition. The signaling value of body features in the case of females seems to be linked to reproductive stage. Sex differences in our bodies depend on fat distribution. The amount of fat in the female body is responsible for a stable household of female sex-steroids. Thus the amount of visible fat can predict if a female is receptive or not. The idea is that body fat must be distributed over prominent places like breasts and buttocks in order to strengthen signal value and not restrict the body's ability to move and function. Indeed, for example breast size correlates with overall body fat. Furthermore, overall weight is linked to fertility: thick mothers have more children. Women presented with a hyper-male face judged its owner as uncaring, aggressive and unlikely to be a good father. Female preference in male faces oscillate in tandem with the menstrual cycle, David Perett Nature June 1994, when a woman is ovulating she tend to prefer men with more masculine features; at less fertile times in her monthly cycle, she favors male faces with a softer, more feminine look....
