Human Development: Research Designs & Nature vs. Nurture

Studying Human Development

• Human development studies changes in people as they age, from conception to death, considering biology, environment, and social interactions.

Research Designs

• Longitudinal design studies the same group of people over a long time, tracking age-related changes within individuals.
  • This design encounters challenges like length, expense, participant attrition due to loss of interest, relocation, or mortality.
• Cross-sectional design studies different age groups at one point in time.
  • It is quick, inexpensive, and easier to conduct but compares different individuals, introducing cohort effects.
  • Cohort effect: occurs when a group of people share a common time period or life experience.
• Cross-sequential design combines cross-sectional and longitudinal approaches by studying different age groups and following them over time.

Nature vs. Nurture

• Nature: inherited characteristics influencing personality, growth, intellect, and social interactions.
• Nurture: environmental influences like parenting, surroundings, and economic factors on development.
• Behavioral genetics studies the impact of genetic inheritance versus experiences on behavior.
• Family studies correlate behavioral traits among family members to assess genetic influence.
• Adoption studies compare traits between adoptive and biological parents to distinguish nature from nurture.
• Twin studies compare trait frequencies in identical (100% shared genes) versus fraternal twins (50% shared genes).
  • Concordance rates indicate the presence of shared traits among twins.
  • A 60% concordance rate means 6 out of 10 twins share a trait.
  • A 20% concordance rate means 2 out of 10 twins share a trait.
  • If a trait was purely genetic, identical twins would have a 100% concordance rate.

Basic Building Blocks of Development

• Genetics studies hereditary, including genes' transmission of human traits and characteristics.
• DNA contains the genetic material of an organism, composed of sugar-phosphate strands linked by amines.
• Genes are DNA segments with a specific arrangement of chemical elements.
• Chromosomes are tightly wound DNA strands.
  • Humans have 46 chromosomes per cell, 23 from each parent.
  • Autosomes: 22 pairs determining most characteristics.
  • The 23rd pair determines sex: XX (female) or XY (male).
• Dominant genes are more active and expressed in observable traits.
• Recessive genes only influence trait expression when paired with an identical gene.
• Polygenic inheritance occurs when traits are influenced by multiple gene pairs, like hair and eye color.
• Some genes can be equally dominant or recessive, leading to mixed traits.
• Huntington's disease and Marfan syndrome are caused by dominant genes.
• Recessive gene disorders include cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and phenylketonuria.
• Chromosomal problems can occur when chromosomes don't separate properly.
• Down syndrome results from an extra chromosome in the 21st pair.
  • This leads to distinct physical features, intellectual disability, and increased health risks.
• Klinefelter syndrome features an XXY sex chromosome combination, resulting in a male with reduced masculine traits.
• Turner syndrome involves a single X chromosome, causing short stature and underdeveloped sexual characteristics in females.

Prenatal Development

• Fertilization: Egg and sperm unite, the resulting cell has 46 chromosomes.
  • Sperm: Male sex cell.
  • Ovum: Female sex cell.
  • Zygote: Fertilized egg cell.
• Monozygotic twins result from one zygote splitting into two masses of cells.
  • They have identical features due to the same set of chromosomes.
• Dizygotic twins result from two eggs fertilized by separate sperm.
  • This is more likely with fertility treatments.
• Multiple pregnancies are higher risk, often resulting in premature birth and low birth weight.
• Selective termination may improve the survival chances of the remaining babies in multiple pregnancies.
• Bioethics studies ethical issues arising from advances in biology and medicine.
• Twins, especially those separated at birth, are valuable for nature vs. nurture studies.

Stages of Development

• Germinal, embryonic, and fetal periods.

Germinal Period

• The zygote undergoes cell division moving down to the uterus to implant.
• Germinal period: The first two weeks after fertilization
  • The placenta forms and provides nourishment.
  • The umbilical cord connects the organism to the placenta.
  • Stem cells differentiate into specialized cells.
  • Stem cells: Immature cells produce more cells.

Embryonic Period

• Embryo: name for the developing organism from 2 weeks to 8 weeks after fertilization
• Embryonic period: 2-8 weeks after fertilization
• Major organs and structures develop.
• By the end, the embryo is about 1 inch long with basic features and a beating heart.

Critical Periods

• The embryo becomes vulnerable to teratogens entering from the placenta.
• Critical periods: times during which certain environmental influences can have an impact on the development of the infant
• Structural abnormalities, like limb or heart defects, occur if exposed at certain weeks.
• Central nervous system: 2 to 5 weeks
• Prenatal Hazards: Teratogens
• Teratogen: any factor that can cause a birth defect (drug, chemical, virus or other actor that can cause a birth defect)
• Fetal alcohol spectrum disorders (FASD) include physical, mental, and behavioral problems.
• Exposure to alcohol is a leading cause of intellectual disability.

Fetal Period

• The age range from 8 weeks after conception until birth.
• Tremendous growth and organ development.
• The organism is then known as a fetus.
• Most babies are born between 38 to 40 weeks.
• Babies born before 38 weeks are called preterm or premature
• Age of viability (infant can survive outside the womb is between 22 and 26 weeks
• Miscarriage occurs in the first 3 months
• Most likely caused by a genetic defect

Infancy Development

• The respiratory system begins to function, the lungs fill with air.
• Body temperature is regulated by the infant's activity and body fat.
• Babies lose a little weight after birth.
• Preferential looking and habituation study infant preferences and detection of change.
  • Preferential looking involves measuring how long an infant looks at different stimuli.
  • Habituation uses is the tendency for infants to stop paying attention to a stimulus that does not change
  • If the infant dishabituates, the infant is capable of detecting a change
  • Reflexes: Innate behaviors help the infant survive (grasping, startle, rooting, stepping, sucking).
  • These can indicate the health of an infants nervous system.
• Motor milestones develop from head control downward (raising head, rolling, sitting, crawling, walking).
• Motor milestones develop as the infant gains greater control of muscles in the body, from the top of the body downward.
  • Raising head and chest 2-4 months
  • Rolling over 2 to 5 months
  • Sitting up with support 4 to 6 months
  • Sitting up without support 6 to 7 months
  • Crawling 7 to 8 months
  • Walking 8 to 18 months
• Infants have more than 100 billion neurons.
  • There is growth of new dendrites, axon terminals and synaptic connections
  • Synaptic pruning: Unused connections are cleared to make way for functioning connections and cells
• Touch, smell, and taste are well developed at birth.
• Hearing may not reach full potential after the baby is born
• Vision is the least functional sense, taking about 6 months to develop fully (color, sharpness).
  • Can only see clearly about 7-10 inches, about the distance from baby face to mother.
• Infants prefer looking at complex patterns and human faces.
• They possess depth perception as measured by visual cliff experiments.

Cognitive Development

• Brain triples weight in first two years and reaches 90% of adult weight by age 5 due to advances in cognitive development.
• It is defined as: development of thinking, problem solving and memory
• Piaget's theory includes four stages: sensorimotor, preoperational, concrete operations, formal operations.
  • Children form mental concepts or schemas
  • Schemas: A framework that guides organization and interpretation of information, evolves through experiences.
  • Assimilation: Understand new things in terms of schemas they already possess
  • EX: States that an orange is an apple because they are both round
  • Accommodation: Alternating old schemas to fit new information
• Sensorimotor stage (0-2 years): Infants use senses and motor abilities to interact with environment
  • Develop object permanence (objects exist even when not seen)
  • Develop understand concepts and mental images represent objects, people and events
  • Only have involuntary reflexes at birth
  • Symbolic thinking begins at the end of this stage (representing thoughts with symbols, such as words.
• Preoperational stage (2-7 years): Language and concepts develop
  • Young children can mentally represent and refer to objects and events with words or pictures
  • Children can move freely about in their world
  • Pretending and make-believe
  • They cannot conserve, logically reason, or consider many characteristics of an object
  • They are not capable of logical thought at this point
  • Animism: Believe that everything is alive
  • Egocentrism: Inability to see the world through anyone else's eyes (everyone sees what the child sees).
  • Centration: Focus only on one feature of an object which ignoring other relevant features
  • Irreversibility: the inability of the young child to mentally reverse an action
• Concrete operations stage (7-12 years)
  • Capable of logical thought processes, but not yet capable of abstract thinking
  • Centration does not occur
  • Conservative and reversible thinking
  • Think more logically
  • Learn science and match
  • Inability to deal with abstract concepts
• Formal operations stage (12-adult)
  • Adolescent becomes capable of abstract thinking
  • Use abstract reasoning about hypothetical events or situations
  • Use abstract analogies
  • Examine and test hypotheses
  • Understand concepts that have no physical reality
  • Involved in hypothetical thinking or thinking about possibilities and impossibilities
  • Only HALF of ADULTS reach this stage
• Educators use Piaget's theory, letting children learn at their own pace and providing hands-on learning.
• Vygotsky's theory emphasizes social and cultural interactions with skilled individuals.
  • Scaffolding: A skilled learner helps a less skilled learner, reducing assistance as they improve.
  • Zone of proximal development (ZPD): the difference between what a child can do alone and with help.
  • Vygotsky believed that private speech is a way for the child to think out loud (not egocentric like piaget)
• Austism is a neurodevelopmental disorder that causes problems in thinking, feeling language, and social skills in relating to others
  • Austism affects thinking, language, and social skills.
  • Theory of mind: The ability to understand other people's beliefs and intentions.
  • People with autism often lack a theory of mind
• Temperament: Behavioral characteristics established at birth (easy, difficult, slow to warm up).
  • Easy babies are regular in their schedules, happy, and easily soothed
  • Difficult babies have irregular schedules, are unhappy with change, and are loud and crabby babies.
  • Slow to warm up: quieter, and slow to adapt to change.
  • Temperament lasts into adulthood and is influenced by heredity and somewhat by environment
  • "poor fit" between parent and baby temperament makes it more difficult to form bond