Tiffany Field,

Touch has been called "the mother of the senses": perhaps because it was the first to develop in evolution. Touch is defined as "the most general of the bodily senses, diffused through all parts of the skin, but in humans, especially developed in the tips of the fingers and the lips." The fingers and lips have a disproportionately large number of neurons that travel to and from the brain. Thus they are the means by which the infant does most of its early learning; hence the need for “baby-proofing.” Touch is the earliest sensory system to develop. When a human embryo is less than an inch long and less than two months gestation, the skin is already highly developed. For example, when the palm is touched at two months gestation, the fingers grasp the palm. The fingers and thumb will close at three months when the palm is touched. Touch can have strong effects on our physiology. When the skin is touched, that stimulation is quickly transmitted to the brain, which in turn regulates our physiology.