The competition will be for the sex with the greater parental investment. Similar phenomena occurs in bird species where males account for the majority of egg-hatching time in the nests. Another salient characteristic in humans is the ratio of the circumference of the hips to the waist. Singh found that a small waist set against full hips was a consistent feature of female attractiveness, while bustline, overall body weight, and physique varied over the years. This universal preference has selected for men who are able to provide for potential offspring through the resources they are able to devote.
Men then have to be more competitive with each other for access to women.
This has created a strong demand for men who are able to provide valuable resources, resulting in the characteristics of assertiveness, aggressiveness, and sensitivity to hierarchy found in men. Dominant behavior in females was not related to sexual attraction in males. Although male dominance enhanced their sexual attractiveness, it did not improve their general likability. For men who were high in agreeableness, dominance enhanced their physical attractiveness significantly. The authors cautioned that overt mate choices made in one context may reflect social coercion.