CHAPTER 2

NATURE WITH NURTURE

Chapter 2

How have ideas about nature and nurture changed?

What are genes? What exactly do they do?

What is the “environment”?

How do the genetic code and environmental contexts interact in development?

PERSPECTIVES ON NATURE AND NURTURE

Development is driven by nature.

Development is driven by nurture.

Development is part nature, part nurture.

Development results from the interplay of nature and nurture

Nature vs. Nurture

• Dispute over the relative importance of hereditary and environmental factors in influencing human development

Nature vs. Nurture

Nature• Heredity factors such as our

genes and chromosomes that we receive from our parents.

Nurture

• Referred to as the environmental factors—how the child is brought up, SES, etc.

DEVELOPMENT IS DRIVEN BY NATURE

• Preformationism

• Rousseau’s innocent babes

• Genetic determinism and eugenics

DEVELOPMENT IS DRIVEN BY NURTURE

• The Blank Slate

• Locke’s view of the mind “tabula rasa”

• Watson’s Behaviorism: strict “fundamentalist” version of environmentalism

DEVELOPMENT: PART NATURE, PART NURTURE

• Heritability

• Degree to which different traits are influenced by genetic factors

• Twin studies

• Adoption studies

• Family relatedness studies

FIGURE2.2: HERITABILITY OF TRAITS IN TWINS

DEVELOPMENT RESULTS FROM THE INTERPLAY OF NATURE AND NURTURE

• Contemporary view of relationship between nature and nurture

• Darwin’s Influence– Theory of evolution– Survival of the fittest and natural selection

• A gradual process of increasing complexity due to interaction between heredity and the environment: http://www.5min.com/Video/Laurence-Steinberg-on-the-Nature-vs-Nurture-Debate-304230832

• Epigenesis: http://learn.genetics.utah.edu/content/epigenetics/twins/

The Genetic Code

• DNA—the chemical that is the basis for heredity

• Chromosomes are strands of DNA that carry genes, which are smaller segments of DNA

• The chromosomes are twisted into a structure that looks like a long spiraling ladder called a double helix

• The steps of that ladder are made of pairs of chemical units called bases

• There are 4 bases that are the “letters” of the genetic code:– A—Adenine– T—Thymine– C—Cytosine– G—Guanine

The Genetic Code

• Genes are the units of heredity

• Each gene is located in a specific position on its chromosome and has thousands of bases

• The sequence of the bases tells the cell how to make proteins that enable the cells to carry out their particular functions

Genotypes and Phenotypes

Phenotype—the observable (expressed) traits and characteristics of a person

Genotype—your underlying genetic makeup which contains both the expressed and the unexpressed traits and characteristics

Sexual Reproduction

Mitosis• Mitosis—the process through

which cells (other than reproductive cells) divide

• Each resulting cell gets a full copy of all 46 chromosomes

• Every cell in your body except the sex cells (sperm and ova) has 23 pairs of chromosomes—46 in all

• http://www.youtube.com/watch?v=Ba9LXKH2ztU&feature=related

Meiosis• Meiosis—the process through

which gametes are produced• Gametes are reproductive cells—

the sperm in males and the ova (eggs) in females

• Meiosis produces cells with only half a set of chromosomes

• Through meiosis each sex cell ends up with only 23 chromosomes instead of 46 as in mitosis

Sexual Reproduction

• Fertilization –2 reproductive cells merge—mother’s and father’s chromosomes link

• Each person has 2 sets of chromosomes and so has 2 copies of every gene—called alleles

• http://www.youtube.com/watch?v=2cwXD6Qc-NU&feature=related

What determines sex?

XX XY XX XY Girl Boy

GENE-GENE INTERACTION

• Sex determination• Additive heredity

–Child’s visible traits, phenotype, is mix of mother’s and father’s traits

• Dominant/Recessive heredity–One version of gene dominant over another

• Regulator genes–Some genes turn other genes on and off

• Environmental influences

ECOLOGICAL PERSPECTIVE

• Bronfenbrenner compared context of development to Russian nested dolls.

• Microsystems –setting in which individual interacts with others face-to-face every day

• Mesosystem –ways in which microsystems are connected

• Exosystem –contexts outside the individual’s immediate, everyday experience

• Macrosystem –larger forces that define a society at a particular point in time