Final answer:
Neurons may die during development through apoptosis, a planned process during growth, or due to genetic and environmental factors that affect brain development and lead to developmental disorders like ASD.
Step-by-step explanation:
Some neurons die during development due to a process known as programmed cell death, or apoptosis. This is a normal part of development, where cells that are only temporarily required for maturation processes are systematically removed when no longer necessary. Factors contributing to neuronal cell death can be genetic defects or adverse environmental conditions during development.
In developmental disorders, like autism spectrum disorder (ASD), the brain regions may not be visibly damaged but could be improperly connected to other regions, affecting their function. On the other hand, neurogenesis, the production of new neurons from undifferentiated neural stem cells, is very limited in adult humans, so the loss of neurons is not easily compensated.