Teratology is the study of abnormalities of physiological development. It is often thought of as the study of human birth defects, but it is much broader than that, taking in other non-birth developmental stages, including puberty; and other non-human life forms, including plants. A newer term developmental toxicity includes all manifestations of abnormal development, not only frank terata. These may include growth retardation or delayed mental development without any structural malformations.