[4] In Maboko Island (1988), the lower jaw of a Kenyapithecus was found, and it provides signs of the simian shelf evolution in modern apes.
This sign of evolution was identified as shown through the lower incisors that lean forward and are known to be used to break hard objects.
It was found in a study that the human chin has no true purpose because the simian shelf in chimpanzees is to protect the jaw from the stress of eating and/or chewing.
[11] The shifting that occurs with the simian shelf may show that "the suprahyoid muscles have a significant influence on the anterior growth of the symphysis".
[10] The forming of the simian shelf occurs due to the "basal symphysis [being] modified" as a result of the v-shape being maintained past the fetal stage.