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Chapter 2: Biological Beginnings

Chapter Outline

  • The Evolutionary Perspective

  • Genetic Foundations of Development

  • Reproductive Challenges and Choices

  • Heredity-Environment Interaction: The Nature-Nurture Debate

The Evolutionary Perspective

Topics

  • Natural selection and adaptive behavior

  • Evolutionary psychology

Natural Selection and Adaptive Behavior

  • Natural selection: An evolutionary process by which individuals of a species that are best adapted are the ones that survive and leave the most fit offspring.

  • Adaptive behavior: Behavior that promotes an organism’s survival in the natural habitat; because an organism possesses characteristics needed for survival.

Evolutionary Psychology
Overview

  • Evolutionary psychology: Emphasizes the importance of adaptation and reproduction to ensure survival. Offspring that adapt, develop behaviors, and possess self-protective traits are more likely to survive.

  • Evolutionary developmental psychology: This field of interest uses the concepts of evolutionary psychology to understand human development. Psychological mechanisms are domain-specific; for example, we have developed sets of problem-solving skills for recurring problems like finding food.

Connectivity to Life-Span Development

  • The benefits conferred by evolutionary selection decrease with age.

  • Natural selection primarily operates during the first half of life and during reproductive viability.

  • Older adults weaken biologically and rely more on cultural resources such as cognitive skills, literacy, medical technology, and social support.

Criticisms of Evolutionary Psychology

  • Criticisms include:

    • Does not adequately value social and environmental factors.

    • Relies on after-the-fact explanations.

    • Cannot be tested scientifically.

    • An alternative bidirectional view posits that environmental and biological conditions influence each other.

    • It is argued that humans have used their biological capacities to produce diverse cultures.

Empirical Testing of Evolutionary Concepts

  • Evolution occurs on a time scale that does not lend itself to empirical study.

  • Ideas from evolutionary psychology may be best tested by studying specific genes in humans and other species, and their links to traits and behaviors.

Genetic Foundations of Development

Topics

  • The collaborative gene

  • Genes and chromosomes

  • Genetic principles

  • Chromosomal and gene-linked abnormalities

The Collaborative Gene
Basic Components

  • Human life begins as a single cell. The nucleus of each cell contains chromosomes:

    • Chromosomes: Threadlike structures composed of deoxyribonucleic acid (DNA).

    • DNA: A complex double-helix molecule containing genetic code or information.

    • Genes: Units of hereditary information made up of DNA; they help cells to reproduce and manufacture proteins that maintain life.

Gene Location and Human Genome Project

  • Each gene has a specific location on a chromosome.

  • The Human Genome Project: Mapped the human genome, revealing that humans have about 22,000 genes that work together with various nongenetic factors.

Gene Expression and Influences

  • Whether a gene is expressed depends on collaboration.

  • Genetic expression is affected by the environment:

    • Hormones in the blood can turn genes "on" and "off."

    • Environmental factors like stress, exercise, nutrition, and temperature can influence gene expression through mechanisms such as methylation.

Genes and Chromosomes
Cellular Structure and Reproduction

  • Excluding sperm and egg cells, all cells in the human body have 46 chromosomes arranged in 23 pairs.

  • Mitosis: Cellular reproduction process in which the nucleus duplicates itself into two new cells, each containing the same DNA as the original cell.

  • Meiosis: Cell division that forms eggs and sperm (gametes).

  • Fertilization: The reproductive stage when egg and sperm fuse, creating a zygote: a single cell that contains 23 unpaired chromosomes from each parent.

Chromosomal Variability

  • Variability arises from combining the genetic material of two parents through the zygote.

  • Identical twins (monozygotic twins): A single zygote that splits into two genetically identical individuals.

  • Fraternal twins (dizygotic twins): Two eggs fertilized by different sperm create two genetically nonidentical zygotes.

Sources of Genetic Variability

  • Mutated gene: A segment of DNA that has been permanently altered.

  • Susceptibility genes: Increase vulnerability to particular diseases or accelerate aging.

  • Longevity genes: Reduce vulnerability to certain diseases and increase the likelihood of longer life.

Genotype and Phenotype

  • Genotype: An individual's genetic material.

  • Phenotype: Observable and measurable physical and psychological characteristics influenced by the genotype and environmental factors.

    • Example: A genetic potential for height may be limited by inadequate nutrition.

Genetic Principles
Dominant-Recessive Genes Principle

  • One gene in a pair can dominate and override the other gene's potential influence on characteristics.

Sex-Linked Genes and Disorders

  • X-linked inheritance: A mutated gene on the X chromosome usually affects males due to their single X chromosome.

Genetic Imprinting

  • A process whereby gene expression differs based on whether the gene is inherited from the mother or the father. This process can disturb development and cause disorders like growth disorders or cancer.

Polygenic Inheritance

  • Multiple genes and environmental influences determine traits or diseases, examined through gene-gene interaction.

Chromosomal Abnormalities
Down Syndrome and Related Disorders

  • Down syndrome: Caused by an extra chromosome 21, resulting in intellectual and physical disabilities.

  • Other sex-linked chromosomal disorders include:

    • Klinefelter syndrome (XXY): Extra X chromosome in males leading to underdeveloped testes and other symptoms.

    • Fragile X syndrome: Abnormality in the X chromosome causing learning disabilities.

    • Turner syndrome (XO): Missing or partially deleted X chromosome in females leading to intellectual disability.

    • XYY syndrome: Males with an extra Y chromosome, typically resulting in above-average height.

Treatment and Prevalence of Chromosomal Abnormalities

  • Down syndrome: Treatment includes surgery and special learning programs; prevalence varies with maternal age.

  • Klinefelter syndrome: Hormone therapy helps alleviate effects; occurs in 1 in 1,000 male births.

  • Fragile X syndrome: More common in males, treated through special education interventions.

  • Turner syndrome: Hormone therapy is essential for development.

  • XYY syndrome: No treatment required.

Gene-Linked Abnormalities
Genetic Disorders Overview

  • Phenylketonuria (PKU): Inability to metabolize phenylalanine; untreated leads to serious conditions.

  • Sickle-cell anemia: Affects oxygen transport in red blood cells, prevalent among African descent populations.

  • Cystic fibrosis: Affects mucus production and leads to reduced lifespan; treated with therapy and antibiotics.

  • Diabetes: Resulting from insulin deficiencies; requires monitored treatment.

  • Huntington's disease: Affects the central nervous system, with symptoms typically occurring after age 35.

Genetic Testing and Predictive Medicine

  • Identifying genetic flaws helps medical professionals predict risks and recommend healthy practices.

Reproductive Challenges and Choices

Topics

  • Prenatal diagnostic tests

  • Infertility and reproductive technology

  • Adoption

Prenatal Diagnostic Tests
Overview

  • Tests to determine fetal health include:

    • Ultrasound sonography

    • Brain-imaging techniques

    • Chorionic villus sampling and Amniocentesis

    • Maternal blood screening and cell-free DNA testing

    • Noninvasive prenatal diagnosis (NIPD)

    • Fetal sex determination

Infertility and Reproductive Technology
Definitions

  • Infertility: Inability to conceive after 12 months of regular intercourse without contraception.

  • In vitro fertilization (IVF): Eggs and sperm are combined in a lab; zygotes transferred into the uterus. Multiple zygotes can increase health risks. Success rates vary by mother's age.

Adoption
Overview

  • Adoption establishes a legal parent-child relationship between non-biologically related parties.

  • Diversity in adoption today includes:

    • Children from many ethnic and cultural backgrounds.

    • Special needs children.

    • Children from neglectful or abusive situations.

  • Outcomes: Adopted children generally fare better than those in long-term foster care, especially when adopted at an early age.

Heredity-Environment Interaction: The Nature-Nurture Debate

Topics

  • Behavior genetics

  • Heredity-environment correlations

  • The epigenetic view and gene × environment (G × E) interaction

  • Conclusions about heredity-environment interaction

Behavior Genetics

  • Behavior genetics: Field studying the effects of heredity and environment on differences in traits, development, and behavior.

  • Twin study: Compares behavioral similarities of identical twins to those of fraternal twins.

  • Adoption study: Compares adopted children's characteristics with those of their adoptive versus biological parents.

Heredity-Environment Correlations
Types

  1. Passive genotype-environment correlations: Occur when biological parents provide a rearing environment compatible with their own genetic tendencies.

  2. Evocative genotype-environment correlations: Characteristics created by a child’s genetics elicit responses from the environment that support specific traits.

  3. Active (niche-picking) genotype-environment correlations: Children seek environments that reflect their interests and talents.

The Epigenetic View and Gene × Environment (G × E) Interaction

  • Epigenetic view: Development results from an ongoing interplay between heredity and environment.

  • G × E interaction: Interaction between specific DNA variations and aspects of the environment.

Conclusions about Heredity-Environment Interaction

  • Contributions from heredity and environment are not additive; complex behaviors arise from their interaction, creating unique developmental paths waiting to be authored through environmental changes.