The aim of facial feminization surgery (FFS) is to eliminate or reduce many of the cross-gender-related deformities of the facial bones caused by late-pubertal testosterone masculinization in MtF transsexuals. facial masculinization effects in male-to-female (MtF) transsexuals can be every bit as disfiguring and socially damaging to them as are the effects of severe facial disfigurement in accident victims and genetic facial deformities in children. In the case of transsexual women, Dr. Pichet focusses on how to adjust the dimensional parameters of each face towards the normal female range, based on certain physical anthropological measurements. Survival requirements over evolutionary time have adapted human males' faces for protection in hunting and fighting, providing them with protruding browridges and heavy jaws/chins. However, human females' faces have evolved (as have childrens' faces) for better hiding/fleeing by having better unobstructed peripheral vision (with the eyes more forward in the facial structure, and with no browridge). These differences in secondary sex characteristics are caused by the different sex hormones present in the bodies of boys and girls after puberty.