What role does apoptosis play in normal development and differentiation?

Apoptosis, or programmed cell death, also plays a crucial role in development.

For example, more neurons are produced during development of the vertebrate nervous system than exist in the adult. That is because neurons survive if they make connections with other neurons during development and self-destruct if they do not.

Also, during early embryonic development, cells that make up webbing between fingers and toes undergo apoptosis. The webbing is eliminated, so fingers and toes can separate. However, some human babies are born with residual webbing, the result of incomplete apoptosis during embryonic development.