Lifespan Development

The purpose of this section is to give you a basic introduction to the concepts and theories in different areas of developmental psychology – the study of how people change across the lifespan. I will do my best to keep this section organized, but it can get a little messy.

The study of developmental psychology is a comparatively knew idea. Although antiquated ideas loosely associated things like “bloodlines” with different behaviors, there were no truly cogent investigations into the ways that people and their personalities change over time. For example, we take for granted now that children have different cognitive abilities than adults, not just in terms of knowledge but in terms of cognitive processes. This was not always the case. We also tend to take for granted the idea that events which occur in infancy or childhood can have life-altering effects.

The first real theory of developmental psychology was Freud’s psychosexual stages of personality development, part of his psychoanalytic framework. Freud attempted to create a comprehensive model which would explain how different experiences and relationships would affect each distinct stage of child development, with an eye toward explaining how these events affect adult personality and, in particular, mental illness. We will take a look at that later on in this unit.

 

Heredity: Genetic Contributions

Developmental psychologists have to have a basic understanding of the nature-nurture issue if they are going to create an accurate picture of things. Strictly speaking, heredity and hereditary issues are a one-time, limited event. At the moment of conception your genetic makeup is set in stone – 23 chromosomal pairs which are made up of strands of DNA. Your complete set of chromosomes is called your genotype, and variations in each chromosome from one person to the next are called alleles. When you receive your parents’ DNA, you get two chromosomes per pair – one from each parent. Alleles are differences between the members of each pair – for example, your mother might have given you a gene for red hair, but your father gave you a gene for brown hair.

Whether you will have brown or red hair (or any other trait) depends on the interaction between the members of each chromosomal pair. Alleles can be either dominant or recessive – if you have one dominant and one recessive trait, then you will express the dominant trait. Recessive traits are only expressed if there are two recessive alleles. Take color-blindness, for example. Color-blindness is a recessive, sex-linked trait (meaning that it is encoded onto one of the sex chromosomes, in this case the X). In order for females to be color blind, they need to get the recessive allele on both their mother’s X and their father’s X. If one of their parents is not a carrier, then that X will contain the dominant allele for color vision. On the other hand, male children are only given one X chromosome (from the mother) and a Y chromosome (from the father). This means that there is only one gene for color vision, and if that gene codes for color-blindness, then the child will be color-blind. This, and not the relative size of the X and Y chromosomes, explains why color-blindness is more likely to occur in males than in females.

In contrast to the genotype, which is the code itself, phenotypes are the expression of a genotype which has been acted upon by environmental forces. These environmental forces can be things like malnutrition during fetal development, epigenetic events such as stress or radiation, teratogens such as lead or thalidomide, or even education. Different genotypes respond differently to environmental events, producing genetic predispositions or resistances. For example, a much greater percentage of the population carries the genes for schizophrenia than the percentage who actually have symptoms. Environmental events (such as trauma) can act as triggers for individuals who have this genetic predisposition. Similarly, not all people with genes which predispose them to high blood pressure and high cholesterol actually have those traits – behavioral and environmental changes can either trigger or inhibit these potential genetic expressions.

Another example is that, although individuals who are of ashkenazi jewish lineage have been shown to have a genotype which codes for resistance to certain cancers, diabetes, and premature ageing, exposure to high levels of radiation or toxic substances could still cause cancer. It is less likely to happen, but the expression of the gene’s code can be affected by environmental factors. Evidence also exists which suggests that gene function can be permanently altered. The study of this phenomenon is called epigenetics, and it focuses on the chemical tags which control gene expression. Although the genes themselves are not altered, their function and expression can be.

 

Prenatal Development

Prenatal development is development prior to birth, in utero. We subdivide prenatal development into three stages: germinal/zygotic, embryonic, and fetal.

• In the germinal stage, rapid cell division occurs and begins to form the foundation of mature organ systems. The zygote implants on the uterine wall at this time, and the placenta and umbilical cord begin to form. This will begin the exchange of nutrients and waste via the mother’s blood supply – and subject the developing zygote to potentially harmful substances (teratogens) in the mother’s blood. This occurs during the first two weeks after conception.
• In the embryonic stage, the placenta and umbilical cord are fully formed. Cell differentiation leads to the differentiation of different organ systems. Sexual differentiation also occurs during this period; prior to differentiation, all embryos have female genitalia. The release of testosterone stimulated by the Y chromosome in males begins the process of transforming the embryo from female to male. This period ends at the end of the second month.
• The fetal stage begins in the third month of pregnancy, and it is during this period that differentiated organ systems mature and begin functioning, cartilage ossifies and turns into bone, and sleep-wake cycles are established.
• Despite the fact that the placenta functions as a filter to protect the embryo/fetus from toxic substances in the mother’s bloodstream, many of these teratogens can still get through and cause harm. These include toxic chemicals such as lead, which has been linked to cognitive deficiencies and behavioral problems. The drop in crime rates from their height in the 80’s to their present-day low numbers probably has something to do with the regulation of lead-based paint in the late 70’s – as fewer children in low-income homes were exposed to paint either in utero or after birth, there was also a general decline in violent crimes.
• Teratogens can also include viruses, prescription drugs, nicotine, and even stress hormones. Exposure to stress in the womb is thought to be an epigenetic event which reduces the child’s resistance to stress on a permanent basis.
• Even a mothers’ psychological state can affect the child’s development – mothers who are depressed, anxious, or subject to chronic stress frequently give birth to children with low birth weight, which carries and increased risk of mortality and infant disease as well as premature birth.

The prenatal period is an extremely vulnerable epoch in an individual’s lifespan. One reason for such a long gestation period (9 months) is that vulnerable systems need this time to mature in a safe environment before being exposed to the outside world. Some systems, such as the developing brain, are uniquely vulnerable to environmental changes and teratogens during the prenatal period, but become more resilient with age.

The most dangerous time period in terms of brain development is the first trimester. During this period the neural tube forms and then closes, leaving solid brain matter (the hindbrain, midbrain, and forebrain) enclosing cavities (ventricles) filled with cerebrospinal fluid. Problems in brain development can range from intellectual and cognitive disabilities due to fetal alcohol syndrome, or problems with closure of the neural tube such as spina bifida and anencephaly (do NOT google image search anencephaly, seriously).

 

Early Infancy – Reflexes, Motor Skills, and Sensory Development

Infants are born with rudimentary motor and sensory abilities, but much of their early behavior is reflexive, rather than voluntary. Infant vitality is measured at birth using the Apgar test, and one of those tests looks for the presence of expected reflexes. These include the rooting, sucking, and grasping reflexes. During the first year of life these reflexes are replaced with voluntary behaviors; their continued presence after 1 year is a sign of neurological problems.As motor skills develop they tend to follow a very specific sequence which follows the patterns of cephalocaudal and proximodistal development. Although infants might not all hit their motor milestones at the same time, they generally hit them in the same order.

Newborn sensory abilities are also somewhat rudimentary, particularly vision. Infants are tuned in to faces but are unable to distinguish or see clear detail for a few months after birth. Other senses, particularly smell, are used to recognize and differentiate between people.

 

Early Infancy – Temperament and Personality

Infant personality is a tricky concept because infants display so few voluntary behaviors in the first few months of life. However, researchers including Thomas and Chess or Jerome Kagan have settled on a few basic patterns of infant behavior which we call temperaments. These patterns are relatively stable in infancy, but don’t necessarily endure into early childhood. So we can distinguish temperament from a more mature notion of personality.

Thomas and Chess described four temperaments: easy, slow to warm up, difficult, and average. The average group consisted of infants whose behavioral pattern did not fit in to any of the other categories. The general focus of their theory is how well the child responds to changing situations; basically, measuring infant adjustment. Easy babies are more eager and responsive to new situations, slow to warm up babies adapt very gradually, and difficult babies are irritable, fussy, and resistant. Kagan’s theory focused on reactivity – whether the child was highly-reactive to new situations (resulting in inhibition) or had low reactivity (resulting in calmer, more sociable behaviors).

 

Language Development

Language development is an extremely important process because it facilitates communication and bonding between the child and its caregivers; in addition, there is a relationship between language development and cognitive development. Here are a couple of basic concepts involved in language development:

• the linguistic acquisition device: Noam Chomsky’s nativist theory of language development suggests that we have an innate, biological disposition to learn language and that neurological structures in early childhood are designed for this purpose. These structures possess the framework of language – universal grammar. Chomsky noted that almost all languages have the same basic parts, and once those parts are mastered, mastering a language is really just about memorizing vocabulary. The most difficult step is understanding the fundamental concept of the relationship between words and meaning.
• the LAD may help to explain the ease with which children learn language; compared to adults learning a second language, children engage in “passive mastery” of grammar concepts and fast mapping of word meanings, and they are able to acquire a large number of words in a very short time.
• the linguistic acquisition device is thought to be in place for a limited time period, and those neural networks which support language learning are re-organized between the ages of 7-9. After this re-organization, language learning shifts to less efficient centers of the brain, which is why it is easier to learn a second language as a child than it is as an adult or adolescent.
• the social context: behavioral theories of language development emphasize that a supportive environment is necessary for a child to learn language. Parents must interact with the child and bridge the gap between infant babbling and true speech, usually by speaking “motherese.” Positive responses from parents reinforce language behaviors that are communicative, rather than just random sounds.
• phoneme distinction, the process of selecting and practicing only language sounds used in your parent language, is a clear example of how positive reinforcement loops have an effect on language development.
• evidence suggests some interplay between behavioral and biological factors. Genie and Isabella, two children who were rescued from isolation at the ages of 13 and 6, respectively, demonstrate the interaction between these factors. Both girls were rescued after being isolated for their entire lives, and as a result neither one had learned how to speak or understand language. They also both had sever cognitive deficits. Isabella, who was younger, responded to remedial efforts to teach her how to speak and understand language. Genie, who was older, was unable to do so.
• In both cases we can see the need for a supportive social context for language development, as well as the limited window for learning language predicted by the LAD (Isabella was not too old, but Genie was).
• During the process of language learning, comprehensive vocabulary is more expansive than production vocabulary.

Language development occurs in four stages. The babbling stage, associated with phoneme distinction; the one-word stage, which is exactly what it sounds like; the two-word stage, where we see the first evidence of grammatical mastery; and the complex speech phase, typically between 36-60 months. By 5-7 years of age most of your language development has finished, and most of the vocabulary which you use on a daily basis was already acquired by the time you were 6 or 7.

 

Gender Development

Gender development is the process by which we form an identity surrounding social ideas of maleness and femaleness. Gender is different from biological sex, which is reflected in our genes. Instead, gender is really about a system of norms and expectations which each society or culture attaches to male and female roles. A person’s gender identity can be different from their biological sex, and gender norms of one culture may be very different from the gender norms of another. Theories of gender development are varied, but the general consensus is that there is an interplay between social, behavioral, and cognitive forces which shapes your gender identity, and that the primary matrix for those forces is play.

Gendered play is nothing new, and it has long been recognized as the practice field for gender roles. Children who play “house” will split up based on gender and perform roles reserved for mothers and fathers, respectively. Social factors certainly play a role in the tendency of children to engage in gendered play: social learning theory suggests that children learn gender roles as a result of reinforcement, vicarious reinforcement, and punishment. Often it is parents or teachers, or even other children, who reinforce gendered behavior or tease (and therefore punish) behavior that is gender-atypical. Children also observe their parents’ expression of gender roles and are vicariously reinforced.

Gender schema theory is a cognitive theory which suggests that our observations of others (particularly parents) help us to develop schema or categories by which we organize behaviors as “masculine” or “feminine.”

Another theory of gender development suggests that there are biological differences between males and females which predispose them to stereotypically gendered behaviors. The case of David Reimer, who was born biologically male but reassigned as female in infancy (including surgery and hormone treatments) is particularly illustrative. Reimer’s parents did their best to socialize Reimer as a female, but despite their efforts Reimer continued to identify as male. Later in life, Reimer underwent penis reconstruction surgery and even married, but eventually committed suicide. His case, and some emerging research in the area, suggests that there might be some aspects of gender identity which are biological.

 

Cognitive Development

Cognitive development refers to the process of developing and accessing intellectual and analytical tools. The most prominent (and frequently criticized) theory of cognitive development is that of Jean Piaget. Piaget’s theory has four distinct stages, and he believed that cognitive development along this sequence was biologically programmed. In particular, he emphasized changes in our schema (patterns of thinking) based on a system of assimilating new information and then accommodating our schema when assimilation is no longer possible. The stages are:

• the sensorimotor stage; in this stage (0-2 years) infant cognition is limited to direct sensory contact with objects. For example, an infant cannot “think” about an object verbally, so instead they may pick the object up or (most frequently) put it in their mouths. Mental representation is still a relatively new skill, and faulty schema such as a lack of object permanence represent the primary developmental hurdles in this stage. Object permanence is the understanding that objects which are out of sight continue to have their own independent existence. The child in this video lacks an understanding of object permanence.
• the preoperational stage; in this stage (2-7) the child is capable of object permanence and the basic elements of symbolic thought. This allows for a better understanding of the nature of reality, as well as communication with others and the use of language (rather than sensation) in cognition. Symbolic thinking manifests in the use of language, and also imagination. Hurdles in this stage include egocentrism (difficulty understanding that other people have a unique perspective) centration (focusing only on one feature of a problem), and irreversibility (the inability to mentally un-do an operation).
• Egocentrism is overcome through socialization, as children get used to the idea of “others” who have unique identities and points of view. This is often referred to as a theory of mind, which can be observed though the false-belief test. Social deficits in autism may be because of neurological problems which inhibit the development of theory of mind.
• Centration is overcome through problem testing and the expansion of your ability to analyse problems from multiple points of view, as is irreversibility. Conservation is a mental operation which is only possible once these milestones have been reached.
• the concrete operational stage; in this stage (ages 7-11) children are able to access more advanced mental operations such as logic. The limitation in this stage is that children in this age range conceptualize of things in concrete terms, rather than abstract ones (i.e., a child is more likely to say “he is my friend because we play together” than he is to say “he is my friend because I can trust him.” Children are capable of using their verbal abilities to analyse logic problems where the conditions line up with their experience, but they are unable to think in terms of abstract concepts or hypotheticals.
• the formal operational stage; from adolescence on, Piaget thought that children develop the ability to engage in “formal operations” such as abstract logic. This is more or less adult-quality cognition.

There are some important criticisms of Piaget’s theory that have led cognitive researchers to tweak his initial assumptions. First, Piaget’s theory neglects the role of a supportive social context, an idea expressed by Lev Vygotsky’s zone of proximal development. Second, Piaget assumed that formal operations was the end-point for cognitive development, but evidence suggests that not only do many people never master abstract reasoning, it has limited purpose for the average person anyway.

Lastly, the notion of cognitive development following distinct stages is generally not borne out by research studies. The information processing model of cognitive development is more helpful insofar as it breaks mental processes up into distinct chains which can develop independently of one another.

 

Transitional Issues in Adolescence

The onset of puberty is one of the key transitional moments in human development. Typical age of onset for females (menarche) is 12, and for males it is 13 (if we consider puberty to begin at the moment when sexual reproduction is possible), although there are wide variances due to social, biological, and environmental factors.

Puberty is important because the hormonal changes, physical changes (growth spurts and development of secondary sex characteristics), and neurological changes all have an impact on identity, health, and behavior. In addition, early puberty for girls (and late puberty for males) are associated with specific social and behavioral problems including increased rate of teen pregnancy, lower income and education levels, and higher rates of dependency on state assistance.

During the course of adolescence the prefrontal cortex of the frontal lobe begins the process of maturation. This portion of the brain is responsible for, among other things, emotional regulation and problem solving, critical thinking and planning, and decision making ability. Adolescents are at a unique point in their development where they are given more responsibilities and freedoms (such as driving) but do not yet have a mature cortex, resulting in mistakes, accidents, and teenage foibles. The prefrontal cortex does not finish maturing until you are around 25, but merely waiting until you are 25 to try to make any decisions won’t speed up the process; the trial-and-error of adolescence plays a vital role in training and pruning neural connections in the cortex.

Adolescence is also the period when we begin to evaluate and attempt to forge our own identities. This is accomplished through experimentation, mentoring, looking to role models, and social reinforcement. James Marcia proposed four kinds of identity status:

• foreclosure, where the individual prematurely decides on a ready-made identity without exploration (such as deciding to run your father’s farm or take over your mother’s business).
• moratorium, where the individual does not yet have a solid identity but feels a push (anxiety) to define themselves in a more concrete way.
• diffusion, where the individual does not have a solid identity and is not experiencing any push or motivation to grow and find themselves.
• achievement, where the individual has actually found an identity that works for them, and settled on it.

Most adolescents are actively in moratorium, and remain there until their mid-twenties.

 

Moral Development

Lawrence Kohlberg developed a theory of moral reasoning in an attempt to explain differences in the way people evaluate moral choices, rather than practical ones. This is a cognitive theory because it focuses on the reason for people’s moral choices. There are three categories (pre-conventional, conventional, and post-conventional) which are each divided into two stages. More or less, moral reasoning follows the same trajectory as cognition in general – moving from direct, physical evaluations to more abstract ones.

Although Kohlberg’s theory seems to suggest a linear model, the truth is that healthy people are flexible in their evaluation of moral situations, depending on the needs of the situation.

 

Please see Psychosocial Development for a discussion of Freud, Erikson, attachment theory, and theories of aging.