Summary

1. The study of human development is a science that seeks to understand how people change or remain the same over time. A scientist begins with curiosity and questions, refines them into hypotheses, then gathers empirical data, and finally draws conclusions that are shared (usually published) with other scientists. A crucial step before the conclusions are accepted is that the research be replicated, to confirm, modify, or refute the conclusions.
2. Nature and nurture always interact. Each human characteristic is affected by the interaction of both genes (nature) and environment (nurture). Gene expression is affected by the environment, beginning at the moment of conception, in a process called epigenesis.

3. Development is multidirectional: Gains and losses are apparent throughout life, and change can be rapid, slow or imperceptible.
4. A multicontextual approach is ecological. That means it takes into account immediate contexts (family, school) as well as broader contexts (historical conditions, socioeconomic status). When a person is born determines their cohort, which influences development lifelong. Poverty also affects development at every age.
5. As the multicultural aspect of the life-span perspective stresses, each culture embraces values and assumptions about human life. Culture, ethnicity, and race are social constructions, that is, concepts created by society. Culture includes beliefs about life and patterns of behavior. Some social scientists want to abandon concerns about race and national origin, while others want to use those concepts to combat racism and cultural prejudice.
6. As emphasized by multidisciplinary concerns, development needs to be understood using the methods and viewpoints of many areas of study. For example, to understand the cause of psychological depression, at least a dozen factors from a dozen disciplines are helpful. Always genes, past history and current age of the person are relevant, so a particular person may be better understood via the perspective of one discipline more than another.
7. Development is plastic, which means that, although inborn traits and childhood experiences affect later development, patterns and possibilities can change throughout life. Further, in differential sensitivity, some people are particularly vulnerable, for better and for worse, to particular genes or experiences.

8. Several specific research designs help scientists understand human development. Scientific observation, the experiment, and the survey each provide insights and discoveries that were not apparent before the research. Each also has liabilities; before conclusions are accepted by the scientific community, several methods are typically used. Statistics, and research on dozens, sometimes hundreds, of individuals are useful in reaching objective conclusions.
9. An additional challenge for developmentalists is to study change over time. Two traditional research designs are often used: cross-sectional research (comparing people of different ages) and longitudinal research (studying the same people over time). A third method, cross-sequential research (combining the two other methods) is more complicated, expensive, and time-consuming, but many developmentalists believe it allows more reliable conclusions.

10. A correlation shows that two variables are related. However, it does not prove that one variable causes the other: The variable thought to be the cause may actually be the consequence, or both variables may be the result of a third variable.
11. Ethical behavior is crucial in all the sciences. Not only must participants be protected and data be kept confidential, but results must be fairly reported, honestly interpreted, and replicated. Scientists must be especially mindful of the implications of their research.
12. Appropriate application of scientific research depends partly on the training and integrity of the scientists. One very important ethical question is whether scientists are designing, conducting, analyzing, publishing, and applying the research needed to help the entire human family develop well.