Females chimps usually have their first baby when they are about 11 or 12 years old. Their gestation lasts for 7 or 8 months,and they usually only have a single baby at a time,although twins are born occasionally. The female has sole responsibility for raising the infant,which she will seldom allow out of her arms. The baby will ride in a cradled position as the mother travels until it is about 5 months old;then will ride piggyback for several more months. It will then get to scamper about in the trees with other young chimps but will remain with its mother until it is about six.