Developmental psychology tries to understand how people change over time. People come fully assembled but not fully operational. We are not prepackaged as a completely formed being. We develop strength and skills. We gain an understand of the world around us and our place within that context.
Lifespan development looks at how people change through their lifespans. It tracks human progress from birth to death. The best developmental research does the same thing: it track people over their lifetimes. This longitudinal research is expensive, difficult to conduct and hard to fund. Often the researchers who start a longitudinal study die before the study is complete. They simply age out.
