using an fMRI, that cute pictures increased brain activity in the orbital frontal cortex. Growth pattern of children Desmond Collins, who was an Extension Lecturer of Archaeology at London University, said that the lengthened youth period of humans is part of neoteny. Physical anthropologist Barry Bogin said that the pattern of children's growth may intentionally increase the duration of their cuteness. Bogin said that the human brain reaches adult size when the body is only 40 percent complete, when "dental maturation is only 58 percent complete" and when "reproductive maturation is only 10 percent complete". Bogin said that this allometry of human growth allows children to have a "superficially infantile" appearance (large skull, small face, small body and sexual underdevelopment) longer than in other "mammalian species". Bogin said that this cute appearance causes a "nurturing" and "care-giving" response in "older individuals". Gender differences The perceived cuteness of an infant is influenced by the gender and behavior of the infant. In the Koyama et al. (2006) research, female infants are seen as cute for the physical attraction that female infants display more than male infants; whereas research by Karraker (1990) demonstrates that a caregiver's attention and involvement in the male infant's protection could be solely based on the perception of happiness and attractiveness of the child. The gender of an observer can determine their perception of the difference in cuteness. In a study by Sprengelmeyer et al. (2009) it was suggested that women were more sensitive to small differences in cuteness than the same aged men. This suggests that reproductive hormones in women are important for determining cuteness. This finding has also been demonstrated in a study conducted by T.R. Alley in which he had 25 undergraduate students (consisting of 7 men and 18 women) rate cuteness of infants depending on different characteristics such as age, behavioral traits, and physical characteristics such as head shape, and facial feature configuration. Preference in young children Borgi et al. stated that young children demonstrate a preference for faces with a more "infantile facial" arrangement i.e. a rounder face, a higher forehead, bigger eyes, a smaller nose and a smaller mouth. In a study that used three- to six-year-old children, Borgi et al. (2014) asserted that the children showed a viewing time preference toward the eyes of "high infantile" faces of dogs, cats and humans as opposed to "low infantile" faces of those three species.