Facial expression responsible for controlling the expression differ in each case. Voluntary facial expressions are often socially conditioned and follow a cortical route in the brain. Conversely, involuntary facial expressions are believed to be innate and follow a subcortical route in the brain. Facial recognition is often an emotional experience for the brain and the amygdala is highly involved in the recognition process. The eyes are often viewed as important features of facial expressions. Aspects such as blinking rate can possibly be used to indicate whether a person is nervous or whether he or she is lying. Also, eye contact is considered
Human skeletal changes due to bipedalism result, in humans the muscles of the forehead (the occipitofrontalis) are only used for facial expressions. Increasing brain size has also been significant in human evolution. It began to increase around 2.4 million years ago but modern levels of brain size were not attained until after 500,000 years ago. Zoological analyses have shown that the size of human brains is significantly larger than what you would expect for our size. The human brain is in fact three to four times larger than its closest relative - the chimpanzee. Even with much modification, some features of the human skeleton remain poorly