Introduction to Human Development

Nature vs. Nurture

Developmental psychology seeks to understand the influence of genetics (nature) and environment (nurture) on human development.

Developmental Psychology

Developmental psychology is the scientific study of changes that occur in human beings over the course of their lives. This field examines change and development across a broad range of topics, such as motor skills and other psycho-physiological processes; cognitive development involving areas like problem solving, moral and conceptual understanding; language acquisition; social, personality, and emotional development; and self- concept and identity formation. Developmental psychology explores the extent to which development is a result of gradual accumulation of knowledge or stage-like development, as well as the extent to which children are born with innate mental structures as opposed to learning through experience.

Nature Versus Nurture

A significant issue in developmental psychology is the relationship between the innateness of an attribute (whether it is part of our nature) and the environmental effects on that attribute (whether it is influenced by our environment, or nurture). This is often referred to as the nature vs. nurture debate, or nativism vs. empiricism. 

• A nativist ("nature") account of development would argue that the processes in question are innate and influenced by an organism's genes. Natural human behavior is seen as the result of already-present biological factors, such as genetic code.
• An empiricist ("nurture") perspective would argue that these processes are acquired through interaction with the environment. Nurtured human behavior is seen as the result of environmental interaction, which can provoke changes in brain structure and chemistry. For example, situations of extreme stress can cause problems like depression.

The nature vs. nurture debate seeks to understand how our personalities and traits are produced by our genetic makeup and biological factors, and how they are shaped by our environment, including our parents, peers, and culture. For instance, why do biological children sometimes act like their parents? Is it because of genetic similarity, or the result of the early childhood environment and what children learn from their parents?

Interaction of Genes and the Environment

Today, developmental psychologists rarely take such polarized positions (either/or) with regard to most aspects of development; instead, they investigate the relationship between innate and environmental influences (both/and). Developmental psychologists will often use the biopsychosocial model to frame their research: this model states that biological, psychological, and social (socio-economical, socio-environmental, and cultural) factors all play a significant role in human development.

We are all born with specific genetic traits inherited from our parents, such as eye color, height, and certain personality traits. Beyond our basic genotype, however, there is a deep interaction between our genes and our environment: our unique experiences in our environment influence whether and how particular traits are expressed, and at the same time, our genes influence how we interact with our environment (Diamond, 2009; Lobo, 2008). There is a reciprocal interaction between nature and nurture as they both shape who we become, but the debate continues as to the relative contributions of each.

Heritability refers to the origin of differences among people; it is a concept in biology that describes how much of the variation of a trait in a population is due to genetic differences in that population. Individual development, even of highly heritable traits such as eye color, depends not only on heritability but on a range of environmental factors, such as the other genes present in the organism and the temperature and oxygen levels during development. Environmental inputs can affect the expression of genes, a relationship called gene-environment interaction. Genes and the environment work together, communicating back and forth to create traits.

Some concrete behavioral traits are dependent upon one's environment, home, or culture, such as the language one speaks, the religion one practices, and the political party one supports. However, some traits which reflect underlying talents and temperaments—such as how proficient at a language, how religious, or how liberal or conservative—can be partially heritable.

This chart illustrates three patterns one might see when studying the influence of genes and environment on individual traits. Each of these traits is measured and compared between monozygotic (identical) twins, biological siblings who are not twins, and adopted siblings who are not genetically related. Trait A shows a high sibling correlation but little heritability (illustrating the importance of environment). Trait B shows a high heritability, since the correlation of the trait rises sharply with the degree of genetic similarity. Trait C shows low heritability as well as low correlation generally, suggesting that the degree to which individuals display trait C has little to do with either genes or predictable environmental factors.

Diathesis-Stress Model

The diathesis–stress model is a psychological theory that attempts to explain behavior as a predispositional vulnerability together with stress from life experiences. The term diathesis derives from the Greek term for disposition, or vulnerability, and it can take the form of genetic, psychological, biological, or situational factors. The diathesis, or predisposition, interacts with the subsequent stress response of an individual. Stress refers to a life event or series of events that disrupt a person’s psychological equilibrium and potentially serve as a catalyst to the development of a disorder. Thus, the diathesis–stress model serves to explore how biological or genetic traits (diatheses) interact with environmental influences (stressors) to produce disorders, such as depression, anxiety, or schizophrenia.

Methods for Researching Human Development

Developmental psychology uses scientific research methods to study the changes that occur in human beings over the course of their lives.

Research Methods

Developmental psychology employs many of the research methods used in other areas of psychology; however, infants and children cannot be tested in the same ways as adults. To study changes in individuals over time, developmental psychologists use systematic observation, including naturalistic or structured observation; self-reports, which could be clinical interviews or structured observation; clinical or case study methods; and ethnography or participant observation. Three research methods used include the experimental, correlational, and case study approach.

Experimental Research

The experimental method involves actual manipulation of treatments, circumstances, or events to which the participant or subject is exposed. This design points to cause-and-effect relationships and thus allows for strong inferences to be made about causal relationships between the manipulation of one or more independent variables and subsequent subject behavior. A limit to this method is that the artificial environment in which the experiment is conducted may not be applicable to the general population.

Correlational Research

The correlational method explores the relationship between two or more events by gathering information about these variables without researcher intervention. The advantage of using a correlational design is that it estimates the strength of a relationship among variables in the natural environment. However, the limitation is that it can only indicate that a relationship exists between the variables; it cannot determine which one caused the other.

Case Study

In a case study, developmental psychologists collect a great deal of information from one individual in order to better understand physical and psychological changes over his or her lifespan. Data can be collected through the use of interviews, structured questionnaires, observation, and test scores. This particular approach is an excellent way to better understand individuals who are exceptional in some way, but it is especially prone to researcher bias in interpretation, and it is difficult to generalize conclusions to the larger population.

Research Designs

Regardless of whether studies employ the experimental, correlational, or case study methodology, they can use research designs or logical frameworks to make key comparisons within research studies. These include longitudinal, cross-sectional, sequential, and microgenetic designs.

Longitudinal Design

In a longitudinal study, a researcher observes many individuals born at or around the same time (a cohort ) and carries out new observations as members of the cohort age. This method can be used to draw conclusions about which types of development are universal (or normative ) and occur in most members of a cohort. Researchers may also observe ways that development varies between individuals and hypothesize the causes of such variation. Longitudinal studies often require large amounts of time and funding, making them unfeasible in some situations. Also, because members of a cohort all experience historical events unique to their generation, apparently normative developmental trends may only be universal to the cohort itself.

Cross-Sectional Design

In a cross-sectional study, a researcher observes differences between individuals of different ages at the same time. This generally requires fewer resources than the longitudinal method, and because the individuals come from different cohorts, shared historical events are not as unique. However, this method may not be the most effective way to study differences between participants, as these differences may result not from their different ages but from their exposure to different historical events.

Cross-Sequential Design

Cross-sequential designs combine both longitudinal and cross-sectional design methodologies. A researcher observes members of different birth cohorts at the same time, and then tracks all participants over time, charting changes in the groups. While much more resource-intensive, this method results in a clearer distinction between changes that can be attributed to individual or historical environment and changes that are truly universal.

Microgenetic Design

Microgenetic design studies the same cohort over a short period of time. In contrast to longitudinal and cross-sectional designs, which provide broad outlines of the process of change, microgenetic designs provide an in-depth analysis of children's behavior while it is changing.