EDUC 107 Chapter 2: [Development - Steinberg] Nature with Nurture

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EDUC 107

Development (Steinberg et al.) Chapter 2: Nature with Nurture DID YOU GET IT • How views of ways in which genetic and environmental forces influence development have changed over time, and how contemporary scientists think about this issue • What genes are, and how they influence development • The difference between mitosis and meiosis • Why a genotype and phenotype can differ • The various levels of context as described in the ecological perspective on development • The different ways in which genetic and environmental influences interact to influence development • In February 2001, scientists published a map of the human genome, the complete set of genes for the creation and development of the human organism o The goal now is to determine which genes influence which characteristics o The hope is that the genome will provide insights into even complex behavior and enable us to prevent or reverse diseases with a genetic component • New research has revealed that genes are more variable and complex than anyone imagined 25 years ago o One cannot understand genes without considering their surroundings • Four main questions: o How have ideas about nature and nurture changed? o What are genes? What exactly do they do? o What is the “environment”? o How do the genetic code and environmental contexts interact in development? Perspectives on Nature and Nurture • Four main views have been put forward about how and why people turn out the way they do, what roles nature/nurture/heredity/experience play in who we become o Development is driven by nature o Development is driven by nurture o Development is part nature, part nurture o Development results from the interaction of nature with nurture • All of these views are still alive in popular culture o Many people believe intelligence is innate (the nature view) o Some people hold that intelligence is more a result of experience, of having well- educated parents, going to good schools, etc. (the nurture view) o Others feel that intelligence is a little bit of both; that is, brains plus upbringing contribute (the nature + nurture position) Development is Driven by Nature • The idea that intelligence and other characteristics are innate, or inborn, not acquired or learned, is called nativism Preformationism • In the 17 century, biologists and others took the concept of inborn traits quite literally o Prevailing view that the embryo was preformed, a miniature adult whose future anatomy was already determined ▪ Some held that the “little person” was in the father’s sperm or the mother’s egg, assuming preformation o Preformationism is the seventeenth-century theory of inheritance that hypothesized that all the characteristics of an adult were prefigured in miniature within either the sperm or the ovum • Accompanied by beliefs about human nature o In general, Western culture has viewed children as innately bad ▪ This outlook comes from the biblical concept of “original sin” ▪ The Puritans, for example, believed that children were by nature evil and vulnerable to temptation • Parents had an obligation to teach children morality, by whatever means necessary, for the child’s own good Rousseau’s Innocent Babes • Jean Jacques Rousseau rejected both preformationism and the idea that children need to be broken like wild horses, rather believing that children are innocent at birth and develop according to nature’s plan o Environment matters, but nature plays the leading role o Infants are not miniature adults and are not rife with temptation, but innocent at birth and the parent’s job is to protect the child from harmful interference and let the child’s development unfold • The open school movement, carried forward today by Montessori schools, hold that children should follow their own interests and not be bound by rigid curricula Genetic Determinism and Eugenics • Genetic determinism is the idea that human qualities are genetically determined and cannot be changed by nurture or education o Preformation and genetic determinism share a central assumption in internal factors controlling development and external factors having little impact th • Carried to an extreme, led to one of the most disturbing chapters in the early 20 century science, the eugenics movement o Eugenics is a philosophy that advocates the use of controlled breeding to encourage childbearing among individuals with characteristics considered “desirable” and to discourage (or eliminate) childbearing among those with “undesirable” traits o (e.g.) Hitler’s effort to “purify” the Aryan race by exterminating Jews, gypsies (or Romany), Poles, homosexuals, and other “undesirables” in Nazi Germany during WWII o (e.g.) advocates of forced sterilization of people who were mentally challenged and other groups in the US as well Development is Driven by Nurture • Environmentalists hold that the newborn is unformed, like a lump of clay, and the individual’s characteristics are entirely the product of experience, upbringing, and learning o External forces are believed to be entirely responsible for development The Blank Slate • John Locke introduced the environmentalist view in “Concerning Human Understanding” o At the time, it was assumed that human nature was predetermined o Locke argued that an infant’s mind is a tabula rasa, or a “blank slate” ▪ Usually associated with Locke, this is the notion that nothing about development is predetermined, and that the child is entirely a product of his or her environment and experience ▪ Childhood is a formative period, and parents have responsibility for teaching children reason, self-restraint, and respect for authority • Whatever successes or failings children exhibit are the result of their experiences • One social consequence of the idea that nurture was the driving force behind development was the mental hygiene movement o Until this time, the “insane” were believed to be possessed by demons and their psychological condition was considered irreversible and threatening o Advocates of mental hygiene took an environmentalist view and held that insanity was an illness that, like other illnesses, could be treated and cured ▪ The first step was “cleaning up” the environment in which disturbed people were housed Watson’s Behaviorism • In academic circles, the two dominant views of development during the first half of the 20 century – learning theory and psychoanalytic theory – saw development primarily as the product of experience, not nature • Watson’s theory of behaviorism was a revival of Locke’s tabula rasa, a strict, “fundamentalist” version of environmentalism o “Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select – doctor, lawyer, artist, merchant- chief, and, yes, even beggarman and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors” • By extension, anyone can become anything if s/he is rewarded (reinforced) o Nurture is everything Development is Part Nature, Part Nurture • By the mid 20 century, many developmental scientists were dissatisfied with botht he nativist and environmentalist views because evidence collected in many fields convinced them that both nature and nurture were critical to development o The central question changed from whether nature or nurture drove development to how much each contributed to different traits o This led to attempts to measure their relative contributions Heritability • Developmentalists began attempting to calculate the degree to which different traits were influenced by genetic factors, or the heritability of the trait o The extent to which a phenotypic trait is genetically determined • This measurement was called the heritability quotient o (e.g.) right- or left-handedness vs. Spanish-speaking • Studies of heritability employed one of several research designs o Twin studies, a method for estimating heritability in which the degree of similarity in a trait that is observed among identical twins is compared with that observed among fraternal twins, took advantage of a “natural experiment” ▪ Identical twins are born when a single fertilized egg divides, resulting in the birth of two individuals whose genetic makeup is identical, and fraternal twins are born when two separate eggs are fertilized, therefore being no more alike genetically than other brothers and sisters ▪ If Identical twins are more alike than fraternal twins on a trait, this trait is more likely to be genetic in origin and have a high heritability quotient ▪ Additional evidence comes from studies of identical twins who were separated at birth and raised in different families • Presumably their similarities are genetic and their differences reflect the environment o Adoption studies, a method for estimating heritability in which similarities between children and their adoptive parents are compared with similarities between children and their biological parents ▪ Several studies found that, at least with respect to intelligence, adopted children resemble their biological parents more than their adoptive ones, but that the quality of the adoptive family environment also matters o Family relatedness studies, a method for estimating heritability by comparing the similarity of children who vary in their genetic relatedness (e.g. siblings, half- siblings, and stepsiblings) ▪ Families that combined children from prior marriages and remarriage are sometimes referred to as blended families and might include stepsiblings, half-siblings, and full siblings ▪ Children with different degrees of relatedness live in the same family and thus grow up in the same general environment ▪ Studies of blended families provide another means to examine the relative contributions of nature and nurture to different aspects of child development • Studies of individuals growing up in blended families have shown that children who are more closely related biologically (i.e. who share more genes in common) are more similar in personality, attitudes, abilities, and behavior than children who grow up in the same family but whose genetic backgrounds are dissimilar • Research on heritability produced some tantalizing results about nature and nurture o Virtually all human traits have substantial heritability but at the same time, these very same traits are also influenced by the environment ▪ Shared environment, in behavioral genetics, is the environment that siblings have in common ▪ Nonshared environment, in behavioral genetics, is the environment that siblings do not have in common, such as the peers with whom they are friends o For virtually all human characteristics, nature and nurture both matter • Heritability studies and the idea that it is possible to accurately estimate how much of a trait is due to genes and how much is due to the environment have been criticized o First, genetic and environmental influences often work hand in hand ▪ Genetic potential and experiences are matched o Second, the idea that genes have the same impact in all environments is questionable ▪ (e.g.) the impact of genes on intelligence is stronger in high-quality environments (which let genes “shine through”) than in low-quality environments, where children do not receive much stimulation and curiosity is discouraged and their innate intelligence remains dormant o Finally, heritability estimates do not consider malleability ▪ Even a trait that is largely inherited can change ▪ Moreover, even genes are flexible • In a nutshell, both nature and nurture count Development Results from the Interplay of Nature and Nurture • The contemporary view of nature and nurture emphasizes interaction, which is more than combination Darwin’s Influence • Charles Darwin is surely the most famous interactionist in Western history o Darwin was not primarily interested in individual development, but rather was a naturalist who devoted his life to understanding the complexity of nature o Yet his ideas have a profound effect on how we view development today • Darwin’s theory of evolution rests on two main ideas: ▪ Typically refers to the variant of the model of evolution formalized by Darwin, which asserts that organisms evolve and change through the process of natural selection o Survival of the fittest ▪ The notion that organisms that are best equipped to survive in a given context are more likely to reproduce and pass their genetic material on to future generations o Natural selection ▪ The process through which adaptive traits that are heritable become more common while maladaptive traits that are heritable become less so Epigenesis • Today most developmental scientists view development as epigenesis, the gradual process through which organisms develop over time in an increasingly differentiated and complex fashion as a consequence of the interaction between genes and the environment o In this view, nothing – or very little – is predetermined, just as in evolution no species’ survival is guaranteed • Epigenesis is rooted in embryology on the one hand, and in the theory of evolution on the other o By the beginning of the 19 century, embryologists had charted the progress of the human embryo and fetus in a timed sequence of changes in structure and function ▪ Biologists could see that the embryo was not a miniature adult ▪ Molecular genetics lay far in the future, but it was clear that prenatal development was a form of biological self-assembly o After Darwin published The Origin of Species, some scientists began to apply the theory of evolution to development ▪ G. Stanley Hall held that the early life of an individual resembled the evolutionary history of the species • The development of the individual repeats the evolution of a species over time • This specific theory was later rejected though o The human embryo does not go through a “fish stage,” a “reptilian phase,” and so on o From the beginning, the embryo is distinctively human • But Darwin’s central concept – change through interaction with the environment – remains a powerful principle in contemporary study of development • Stem cells illustrate epigenesist o Stem cells are primitive, undifferentiated cells or “precells” found in large numbers in the embryo ▪ These cells are the raw material of prenatal development ▪ Each stem cell has a full set of chromosomes and the potential to become anything the body needs o During embryonic development, they become increasingly specialized, eventually developing into blood cells, nerve cells, muscle cells, and so on, and assembling themselves into functioning organs and tissues ▪ This biological process gives us a model for looking at other levels of development • At birth, many traits are like stem cells, a potential that develops and becomes more finely tuned as experiences, relationships, health, nutrition, and physical setting are part of this process o Epigenesis puts nature and nurture back together again as active copartners in development What Are Genes, and What Do They Do? • Genes provide the continuity that makes us human o Direct the cells of an embryo to become a human being o Help to establish our common modes of thinking, feeling, acting, communicating o Contribute to the wide diversity within the human species – in appearance, abilities, health, and even happiness Becoming Human • All humans have some traits in common o Bipedalism, being able to stand and walk on two feet ▪ One of the defining characteristics of our species • Our upright posture and gait are the result of natural selection o These characteristics made our ancestors better adapted to their environemtn than our competitors • Other defining human traits: o Handiness (opposable thumbs, the better to grasp things) o Language o The ability to alter our surroundings o Knack for calculations o Self-awareness • Yet none of these traits, by itself, is unique to humans o Great apes demonstrate self-awareness o Birds and whales communicate through sound and even have local “dialects” o Apes use tools, and so do some birds o Birds build intricate nests, sometimes in “colonies,” and even ants alter their environments o Raccoons as well as primates have opposable thumbs o Orangutans have grasping hands and feet o Parrots and great apes have demonstrated basic comprehension of words, grammar, and number • No other animal develops this combination of abilities so easily or naturally “Like a Rolling Stone” • These universal aspects of human development are under tighter genetic control than other traits o Canalization: the degree to which an element of development is dictated by the common genetic program that all humans inherit • Think of development as a stone rolling down a hill inside a canal • In general, early development is more highly canalized than later development The Importance of Being Cute • One distinctive feature of human development is that we are born “prematurely” o Humans can’t even get from one place to another by themselves until age nine or ten months, when they first begin crawling • One reason for this is that humans have evolved to be highly social animals o A prolonged period of juvenile appearance and behavior promotes the development of social bonds by attracting caregivers to infants and vice versa o Babies of many species are “cute” ▪ A natural cycle of attraction ▪ Both the baby and the adult are “programmed” to form a bond • Another reason for the prolonged immaturity of human infants is that humans depend on learning more than other species do o Our “immaturity” at birth makes us more receptive to environmental influence ▪ Predisposed to learning, thus better able than most other species to change our behavior in response to environmental conditions ▪ Adaptable in part because much of our early development takes place in the world, not the womb o Yet the Human Genome Project reveals that we share some of our genes with even the simplest organisms, such as bacteria and molds o Within the human species, 99.9% of genetic material is identical ▪ Yet we have so many genes that even the small amount we don’t share with others leaves much room for variation Human Diversity • We are related to all living things, and this makes diversity within our species even more remarkable because no two human beings share the exact same genes (except identical twins) The Genetic Code • The nucleus of almost every human cell contains 23 pairs of chromosomes, one set from the individual’s mother and one from the individual’s father o The exceptions are reproductive cells, e.g. sperm and ova • Chromosomes are long strands of DNA (deoxyribonucleic acid) that carry genes and associated proteins o These chromosomes, present in every cell, contain a complete set of instructions for the development of a unqiue human being • The rungs of the DNA ladder consist in pairs of four chemical bases: adenine (A), thymine (T), guanine (G), and cytosine (C) o Adenine always connects with thymine, and guanine with cytosine o The order of base pairs [pairs of adenine and thymine and of guanine and cytosine that make up the “rungs” of the DNA molecule] determines genetic instructions, much as the order of letters determines the meaning of a word • Chromosomes direct activities in the cell by attracting molecules of RNA (ribonucleic acid) o RNA functions as a messenger, carrying genetic instructions out of the cell’s nucleus into the cytoplasm, which contains the raw materials for synthesizing enzymes, hormones, and other proteins ▪ Different proteins are created by combining different amino acids in different ways • Proteins cause chemical reactions in the body that lead to the production and reproduction of cells • Genes are the units of heredity that pass characteristics from one generation to the next o A gene is a segment of DNA, occupying a specific place on the chromosome, and controls a particular aspect of the production of a specific prote
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