The process of growth and development in living organisms is termed ontogeny. Ontogeny encompasses the series of changes that occur from a single fertilized egg to a mature organism, including cellular differentiation, tissue formation, and organ development. It involves both genetic factors and environmental influences, guiding the organism's adaptation and survival. This process varies significantly across species and is essential for understanding developmental biology. The study of ontogeny also provides insights into evolutionary changes and the origins of complex life forms.