Timing - retarded language ability between 6 mos. and 3 years interferes with inherited tendency to be a good public speaker. Disease Intrauterine environment . Prenatal environment of the womb is protected and stable, but a number of conditions can affect embryonic or fetal development before birth if mother's health or nutrition is poor, if she contracts certain diseases, such as German measles or syphilis, uses drugs, or is exposed to X-rays or atomic radiation, the fetus may be harmed. Genetic problems are inherited. Social development .
Infants are social creatures from the day they are born.
Examples of their sensitivity to others is their ability to imitate adults and their interest in the human face.