Chapter 3

Nature vs. Nurture: Interaction Between Genetics and Environment

• The ongoing debate about whether genetics (nature) or environment (nurture) has a greater influence on development.

Theory of Genotype and Environmental Effects

Types of Genotype-Environment Interactions

1. Passive Genotype

   • Parents provide both genes and environment to children.

   • Children's environment is shaped by parental traits and decisions, leading to passive development.

2. Evocative Genotype

   • A child's inherited characteristics elicit responses from the environment.

   • Example: A child’s temperament (e.g., stubbornness) causes parents or peers to react a certain way, shaping the child’s experiences.

3. Active Genotype (Niche Picking)

   • Individuals actively seek environments that complement their genetic predispositions.

   • Example: An intellectually gifted child seeks out educational opportunities, such as libraries or clubs, despite the availability in their initial environment.

Stability of Genotype Effects

• The evocative genotype remains stable over time; traits influence behavior throughout life.

• Example: A stubborn individual will continue invoking specific responses from their environment into adulthood.

Case Study: Minnesota Twin Study

• The Minnesota study investigates the nature vs. nurture debate using twins raised apart.

• Focus is particularly on identical twins, such as Oscar and Jack, who were raised in significantly different environments.

• Key Findings:

  • Despite being raised in different countries and cultures, twins shared similar personalities and habits.

  • Cultural identities and worldviews diverged sharply due to differing environments (e.g., upbringing in Nazi Germany vs. a Jewish upbringing).

• The study demonstrates the profound influence of environment on identity despite genetic similarities.

Human Development: Prenatal Development Overview

Stages of Prenatal Development

1. Germinal Period (Weeks 1-2)

   • Zygote forms after the sperm fertilizes the ovum.

   • Blastocyst forms, comprising of two layers: trophoblast (future placenta) and embryonic disc (future baby).

2. Embryonic Period (Weeks 3-8)

   • Rapid organ development occurs.

   • Embryonic disc differentiates into three layers: ectoderm, mesoderm, endoderm.

   • Neural tube develops into the brain and spinal cord.

3. Fetal Period (Weeks 9-Birth)

   • Major growth phase with organ systems maturing.

   • Fetus becomes more responsive to its environment (e.g., sound).

Important Aspects of Cell Development

• Gametogenesis: Each parent contributes reproductive cells (sperm and ova) via meiosis, resulting in cells with 23 chromosomes.

• Fertilization: Critical timing is necessary for the conception to occur—typically within 24 hours after ovulation.

Blastocyst and Implantation

• Implantation: The blastocyst embeds into the uterine wall, beginning a crucial developmental phase.

• About half of blastocysts face failure to implant due to chromosomal issues.

Development of Organs and Systems

• Major organ systems are formed during the embryonic period, making it a critical stage for exposure to teratogens that may harm development.

• The complete development of the placenta, which filters nutrients and wastes between mother and fetus, is essential for safe gestation.

Considerations for Healthy Prenatal Development

• A pregnant woman’s health, including diet and exposure to harmful substances during early pregnancy, can dramatically impact fetal development.

• Weight management pre and post-birth is crucial for infant health and sustainability.

Summary of Key Points

• The interplay between genes and environment shapes human development.

• Early prenatal development is critical, with potential long-term consequences depending on both genetic and environmental factors.

• Understanding these interactions can help in better supporting healthy pregnancies and child development.