Indeed, according to the research of American scientists, no matter how much a woman weighs, men like women with a waist circumference of 70% of the hip circumference best. In the eyes of men, a woman with a thin waist can be called a real beauty. Why do men like women with thin waists? This is an innate instinct, because waist circumference is the most easily recognized signal, from which a woman's fertility and health can be seen. In the evolution of thousands of years, men naturally like women with strong fertility and good health, while girls with thin waists have strong fertility. This is because women with thin waists have higher estrogen. A girl may have a thick waist in childhood, but once she reaches puberty, after puberty, the girl's estrogen secretion will be strong, her waist will be thin, but her hips will be big, so she looks thin and fat. After middle age, estrogen drops, and the waist circumference will gradually expand, which is why the waist of young girls is very thin, but once they reach middle age, the waist bulges like a bucket. Obesity means low estrogen levels, which also indicates high risk of illness. Imagine, which man has a soft spot for a woman with low fertility and poor health? Of course, modern medicine can accurately identify women's fertility and health problems, but in ancient times when medicine was underdeveloped, British, American and Asian writers could intuitively know the biological relationship between beauty and health. It can be said that a thin waist is the standard of beauty, which is almost determined by human instinct. In all animals, for the sake of population reproduction and inheritance of excellent genes, females always look for the strongest males to mate with, while males also try to find the healthiest females, which is consistent with Darwin's theory of evolution. Women with thin waist will send a valuable message to men, that is, such women are more likely to have healthy offspring and inherit excellent genes from men, which will give men an instinctive attraction. Therefore, men in every era like women with thin waists, and thin waists have thus become the eternal standard for beautiful women.