sagging breasts) is perceived as less attractive and attributed to a woman of older age. These findings are coherent with previous research that link breast attractiveness with female youthfulness. Unlike breast size, breast ptosis seems to be a universal marker of female breast attractiveness. A study showed that men prefer symmetrical breasts. Breast symmetry may be particularly sensitive to developmental disturbances and the symmetry differences for breasts are large compared to other body parts. Women who have more symmetrical breasts tend to have more children. Historical literature often includes specific features of individuals or a gender that are considered desirable. These have often become a matter of convention, and should be interpreted with caution. In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to have small breasts. In Persian literature, beautiful women are said to have breasts like pomegranates or lemons. In the Chinese text Jeweled Chamber Secrets () from the Six Dynasties period, the ideal woman was described as having firm breasts. In Sanskrit literature, beautiful women are often said to have breasts so large that they cause the women to bend a little bit from their weight. In Middle English literature, beautiful women should have small breasts that are round like an apple or a pear. Buttocks Biological anthropologist Helen E. Fisher of the Center for Human Evolution Studies in the Department of Anthropology of Rutgers University said that, "perhaps, the fleshy, rounded buttocks... attracted males during rear-entry intercourse." In a recent study, using 3D models and eye-tracking technology Fisher's claim was tested and was shown that the slight thrusting out of a woman's back influence how attractive others perceive her to be and captures the gaze of both men and women. Bobbi S. Low et al. of the School of Natural Resources and Environment at the University of Michigan, said the female "buttocks evolved in the context of females competing for the attention and parental commitment of powerful resource-controlling males" as an "honest display of fat reserves" that could not be confused with another type of tissue, although T. M. Caro, professor in the Center for Population Biology and the Department of Wildlife, Fish, and Conservation Biology, at University of California, Davis, rejected that as being a necessary conclusion, stating that female fatty deposits on the hips improve "individual fitness of the female", regardless of sexual selection. In a