The shape of evolution.

Thin may be in for many women, but when men appraise a woman's figure, the guiding principle may be "waist not, want not." Men consider a relatively thin waist set against full hips to be a cardinal sign of female attractiveness, regardless of changing cultural conventions about bust size, body weight, or other physical features, contends Devendra Singh, a psychologist at the University of Texas at Austin.

Several million years of evolution may have primed men to perk up at the sight of a curvaceous waist because this aspect of female shape serves as a cue to fertility and health, Singh holds. For instance, evidence now suggests that women whose waists are significantly narrower than their hips (a low waist-to-hip ratio) get pregnant more easily and tend to give birth to their first child at a younger age than women whose waists are closer in size to their hips (a high waist-to-hip ratio).

As with other evolved mental rules-of-thumb that may influence behavior (SN: 10/12/91, p.232), the male preference for slender female waists operates unconsciously within a larger cultural context, the Texas psychologist asserts. Thus, men rate a female "hourglass figure" as sexy or attractive rather than extolling its implications about fertility.

Both Miss America winners and Playboy centerfolds have displayed virtually the same low waist-to-hip ratio for decades, Singh reports in the August JOURNAL OF PERSONALITY AND SOCIAL PSYCHOLOGY. Data for the beauty contestants extended from 1923 to 1987; centerfold measurements existed for 1955 to 1965 and 1976 to 1990. Narrow waists as markers of female attractiveness also appear in Stone Age figurines, early Greek paintings, and fashions emphasizing corsets, bustles, and girdles, Singh argues. Even Twiggy, the 1960s model renowned for her slenderness, had a low waist-to-hip ratio that nearly matched those of the Miss Americas and centerfolds.

Singh also reports that 106 college-age men rated women with a low waist-to-hip ratio as more attractive, healthier, and better able to bear children than women with a high waist-to-hip ratio. Volunteers ranked drawings of four normal-weight (120 pounds) women, four overweight (150 pounds) women, and four underweight (90 pounds) women, all 5 feet 5 inches tall. In each group, waist-to-hip ratios ranged from low to high. Other facial and bodily features stayed the same.

Men most often chose normal-weight figures with narrow hips as most attractive and gave higher overall attraction ratings to normal-weight figures. Men apparently do not equate a thin figure with beauty, Singh contends.

Similar responses to the 12 female figures emerged among 89 men ranging in age from 24 to 85.

These findings must be extended to other cultures, Singh says. She theorizes that a woman's waist-to-hip ratio affects a man's decision to initiate contact with her. Other factors, such as facial attractiveness and compatibility, then come into play.