Hockenbury Discovering Psychology 5th txtbk

370 CHAPTER 9 Lifespan DevelopmentTable 9.1Major Stages of the LifespanStagePrenatalInfancy andtoddlerhoodEarly childhoodMiddle childhoodAdolescenceYoung adulthoodMiddle adulthoodLate adulthoodAge RangeConception tobirthBirth to 2 years2 to 6 years6 to 12 years12 to 18 years18 to 40 years40 to 65 years65 years to deathThe Chapters in Your Life Story If youthink of your life as an unfolding story,then the major stages of the human life -span represent the different “chapters” ofyour life. Each chapter is characterized byfundamentally different physical, cognitive,and social transitions, challenges andopportunities, demands and adjustments.Comparing different life stories revealsmany striking similarities in the developmentalthemes of any given stage. Butbeyond those similarities, every life storyis also characterized by considerable variationsin the timing of life events and thepathways that are ultimately followed. Inthat sense, every life story is unique.stories. As we’ll note several times in this chapter, the typical, or “normal,” patternof development can also vary among cultures.Developmental psychologists often conceptualize the lifespan in terms of basicstages of development (see Table 9.1). Traditionally, the stages of the lifespan aredefined by age, which implies that we experience relatively sudden, age-relatedchanges as we move from one stage to the next. Indeed, some of life’s transitionsare rather abrupt, such as entering the workforce, becoming a parent, or retiring.And some aspects of development, such as prenatal development and languagedevelopment, are closely tied to critical periods, which are periods during which achild is maximally sensitive to environmental influences.Still, most of our physical, mental, and social changes occur gradually. As we tracethe typical course of human development in this chapter, the theme of graduallyunfolding changes throughout the ages and stages of life will become more evident.Another important theme in developmental psychology is the interaction betweenheredity and environment. Traditionally, this was called the nature–nurture issue.Although we are born with a specific genetic potential that we inherit from our biologicalparents, our environment influences how and when that potential isexpressed. In turn, our genetic inheritance influences the ways in which weexperience and interact with the environment (Diamond, 2009).Developmental psychology is a broad field, covering a wide range of topics frommany different perspectives. Our goal in this chapter is not to try to survey theentire field of lifespan development. Rather, we’ll focus on presenting some of themost influential theories in developmental psychology and the key themes that haveguided research on each stage of the lifespan. As we do so, we’ll describe the typicalpatterns of development while noting the importance of individual variation.Genetic Contributions to Your Life StoryKey Theme• Your genotype consists of the chromosomes inherited from your biologicalparents, but your phenotype—the actual characteristics you display—results from the interaction of genetics and environmental factors.zygoteThe single cell formed at conception fromthe union of the egg cell and sperm cell.chromosomeA long, threadlike structure composed oftwisted parallel strands of DNA; found inthe cell nucleus.deoxyribonucleic acid (DNA)The double-stranded molecule that encodesgenetic instructions; the chemical basis ofheredity.geneA unit of DNA on a chromosome thatencodes instructions for making a particularprotein molecule; the basic unit of heredity.genotype(JEEN-oh-type) The genetic makeup of anindividual organism.Key Questions• What are DNA, chromosomes, and genes?• What role does the environment play in the relationship betweengenotype and phenotype?• What is epigenetics?You began your life as a zygote, a single cell no larger than the period at the end ofthis sentence. Packed in that tiny cell was the unique set of genetic instructions thatyou inherited from your biological parents. Today, that same set of genetic informationis found in the nucleus of nearly every cell of your body.What form does that genetic data take? The genetic data you inherited from yourbiological parents is encoded in the chemical structure of the chromosomes that arefound in the cell nucleus. As depicted in Figure 9.1, each chromosome is a long,threadlike structure composed of twisted parallel strands of deoxyribonucleic acid,abbreviated DNA. Put simply, DNA stores the inherited information that guidesthe development of all living organisms.Each of your chromosomes has thousands of DNA segments called genes that arestrung like beads along its length. Each gene is a unit of DNA code for making a particularprotein molecule. Interestingly, genes actually make up less than 2 percentof human DNA (Human Genome Program, 2008). Determining the functionsof the rest of the DNA is an active area of investigation. This DNA was once