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Lecture 3. Heredity and Environment Prenatal Development Birth. Heredity and environment. The case of intelligence. Charles Darwin. Observed that most organisms reproduce at tremendous rates, yet populations remain nearly constant.

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Lecture 3

Heredity and Environment

Prenatal Development


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Heredity and environment

The case of intelligence

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Charles Darwin

  • Observed that most organisms reproduce at tremendous rates, yet populations remain nearly constant.

  • Reasoned that an intense, constant struggle for food, water, and resources must occur among the numerous young born.

  • Those that survive pass on their genes to the next generation.

  • Believed that those who survive are superior to those who do not.

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Natural Selection

  • Natural selection is the evolutionary process that favors individuals of a species that are more adapted to survive and reproduce.

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Francis Galton (1822-1911)

  • Galton: Intelligence is a matter of sensory acuity.

  • Sensory acuity mainly a function of natural endowment  Intelligence inherited.

  • Children of illustrious individuals are far more likely to be illustrious themselves.

  • Eugenics -> Selective breeding.

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Alphonse de Candolle (1806-1893)

  • Climate, religious tolerance, democratic government, and a thriving economy are at least as important as inherited capacity.

  • Galton ->

    • Intelligence tests

    • Concept of Correlation

    • Twins studies

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Modern Twin Studies

  • The behavioral similarity of identical twins is compared with the behavioral similarity of fraternal twins.

  • Identical twins (monozygotic twins) develop from a single fertilized egg that splits into two genetically identical replicas, each of which becomes a person.

  • Fraternal twins (dizygotic twins) develop from separate eggs and separate sperm, making them genetically no more similar than ordinary siblings.

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Issues with Twin Studies

  • By comparing groups of identical and fraternal twins, behavior geneticists capitalize on the basic knowledge that identical twins are more similar genetically than are fraternal twins.

  • However, adults might stress the similarities of identical twins more than those of fraternal twins.

  • Identical twins might perceive themselves as a “set” and play together more than fraternal twins.

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Alfred Binet (1857-1911)

  • First Binet turned to the favored method of Paul Broca  Measured skulls

  • By the end: The idea of measuring intelligence by measuring heads seemed ridiculous.

  • 1904: Psychological methods.

  • Series of short tasks, related to everyday problems of life.

  •  Mental age and Chronological age.

  •  Special educational programs.

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W. Stern (1871-1938)

  • Mental age should be divided by chronological age  Intelligence quotient (IQ).

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Binet’s approach

  • The scores are a practical device.

  • The scale is an empirical guide for identifying children who need help.

  • Emphasis upon improvement through special training.

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  • Intelligence: Means of power and control.

  • Identification of the so called feeble-minded within the USA. Goal: prevent procreation (eugenics).

  • Restriction on immigration of so-called inferior races from Europe.

  • Legitimizing oppression of African Americans by suggesting that they intellectually inferior.

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American psychologists hereditarian theory of IQ.

  • Binet's scores: Measures of an entity called intelligence.

  • Intelligence: Largely inherited

  • Inherited IQ scores: Marked people and groups for an inevitable station in life.

  • Differences between groups: Heredity

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  • Conceptual problem.

  • Equation of "heritable" with "inevitable.”

  • Confusion of within and between-group heredity.

  •  Statistical definition of heritability.

  •  Range of reactions.

  •  If heredity explains a certain percentage of variation among individuals within a group, it must also explain a similar percentage of the difference in average IQ between groups  wrong (two separate phenomena).

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Henry Goddard (1866-1957)

  • Translated the Binet-Simon scale into English.

  • "It is perfectly clear that no feeble-minded person should ever be allowed to marry or to become a parent.

  •  20 states passed sterilization laws.

  • Idiots – Imbeciles – Morons.

  • Immigration: specified European countries for which the percentage of mentally defective immigrants was the highest.

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Lewis Terman (1877-1956)

  • Revised the Binet scale and made it popular. IQ = MA/CA*100.

  • Children should be segregated in special classes and be given instruction which is concrete and practical.

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Robert M. Yerkes (1876-1956)

  • Army Alpha Test: Literate individuals. Army Beta Test: Illiterate individuals

  • “Results”: About half of the white males tested in the army had a mental age of 13 or lower.

  • European immigrants can be graded by their country of origin.

  • Blacks lacks initiative, displays little or no leadership, and cannot accept responsibility.

  •  Immigration Restriction Act of 1924. Quotas against nations of "inferior stock."

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US Black-White mental testing

  • 1897: G. R. Stetson tested 500 African American and 500 European American public school children in Washington, D.C.

  • Children were required to repeat four stanzas of poetry.

  • Black children outperformed the white children  Memory not a valid measure of intelligence.

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  • Arthur Jensen sparked a debate theorizing that intelligence is primarily inherited. Differences between “races” are inherited.

  • Flynn effect:

    • Average IQ test score performance is rapidly rising.

    • The largest Flynn effects appear on so-called culture fair tests

    • Dutch data shows a 21 point difference between 1952 and 1982.

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Down Syndrome

  • Caused by the presence of an extra chromosome

  • Characterized by:

    • round face

    • flattened skull

    • extra fold of skin over the eyelids

    • protruding tongue

    • short limbs

    • retardation of motor and mental abilities

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John Langdon H. Down

  • Physician to the Asylum for Idiots at Earlswood.

  • 1860s: Investigations into the 'structure and function of the various organs' in idiots and imbeciles.

  • Classify idiots on the basis of their resemblance to ethnic groups.

  • Facial features and behavioral attributes of certain idiots -> typical Mongols.

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Conclusions about Heredity-Environment Interaction

  • Both genes and environment are necessary for a person to exist.

  • The emerging view is that genes give people a propensity for a particular developmental trajectory that is ultimately realized through environmental circumstances.

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Prenatal Development

From a zygote, a single cell, the size of a period in your book, to 2 billion cells and weighing over 3kgs.

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The Process of Human Reproduction

  • Reproduction begins when an ovum is fertilized by a sperm.

  • This produces a zygote—a single cell formed through fertilization.

  • In the zygote, two sets of unpaired chromosomes combine to form one set of paired chromosomes.

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The Course of Prenatal Development

  • The Germinal Period

  • The Embryonic Period

  • The Fetal Period

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The Germinal Period

  • It is the period that occurs the first 2 weeks after conception.

  • By about 1 week after conception, the zygote is composed of 100 to 150 cells.

  • This period includes the creation of the zygote, continued cell division, and attachment of the zygote to the uterine wall.

  • Implantation, or attachment to the uterine wall, occurs about 10 days after conception.

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The Differentiation of Cells

  • The Blastocyst - the inner layer of cells that develops during the germinal period and later becomes the embryo

  • The Trophoblast - the outer layer of cells that develops during the germinal period and later provides nutrition and support for the embryo

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The Embryonic Period

  • The period that occurs from 2 to 8 weeks after conception

  • The rate of cell differentiation intensifies, support systems for the cells form, and organs appear

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Cell Layers of the Embryo

  • Endoderm - inner layer; develops into the digestive and respiratory systems

  • Ectoderm - outermost layer; becomes the nervous system, sensory receptors (ears, nose, eyes), and skin parts (hair and nails)

  • Mesoderm - middle layer; becomes the circulatory system, bones, muscles, excretory system, and reproductive system

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Prenatal Life-Support Systems

  • The Placenta - consists of a disk-shaped group of tissues in which small blood vessels from the mother and the offspring intertwine but do not join

  • The Umbilical Cord - contains two arteries and one vein, that connects the baby to the placenta

  • The Amnion - a bag or envelope that contains a clear fluid in which the developing embryo floats

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Important Embryonic Developments

  • 21 Days - Eyes begin to appear

  • 24 Days - Heart cells begin to differentiate

  • Fourth Week - First appearance of the urogenital system, arm and leg buds appear, chambers of the heart take shape, blood vessels surface

  • Fifth to Eighth Week - Arms and legs differentiate further, face starts to form, facial structures

  • 8 Weeks - 2.5 cm long

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Definition of Organogenesis

  • The process of organ formation that takes place during the first 2 months of prenatal development

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The Fetal Period

The period that begins 2 months after conception and lasts, on average, 7 months

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Three Months after Conception

  • The fetus is 7.5 cm long.

  • The fetus becomes active, moving its arms, legs, head, and opening and closing its mouth.

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The End of the Fourth Month

  • The fetus is 15 cm. long.

  • Arm and leg movements can be felt by the mother for the first time.

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The End of the Fifth Month

  • The fetus is 30 cm long.

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The End of the Sixth Month

  • The fetus is approximately 35 cm long.

  • A grasping reflex is present.

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The End of the Seventh Month

  • The fetus is 40 cm long.

  • The fetus is very active.

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The Eighth and Ninth Months

  • The fetus grows longer and gains substantial weight.

  • At birth, the average North American baby is about 51 cm long and weighs 3.2 kg.

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Prenatal Diagnostic Tests

  • Maternal Blood Test

  • Ultrasound Sonography

  • Amniocentesis

  • Chorionic Villi Sampling

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  • A prenatal medical procedure in which a sample of amniotic fluid is withdrawn by syringe and tested to discover if the fetus is suffering from any chromosomal or metabolic disorders

  • Performed between the 12th and 16th weeks of pregnancy

  • There exists a small risk of miscarriage (one in every 200-300)

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Chorionic Villi Sampling

  • A prenatal medical procedure in which a small sample of the placenta is removed

  • Performed between the 8th and 11th weeks of pregnancy

  • Provides information about the presence of birth defects

  • Has a slightly higher risk of miscarriage than amniocentesis

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Sensory Capacities of the Fetus

  • Motion: The vestibular system of the middle ear begins to function in the human fetus about 5 months after conception and is fully mature at birth.

  • Vision: Little is known for certain. At 26 weeks of pregnancy, fetuses respond to light; it causes their heart rate to change.

  • Sound: Research indicates that at 4 months after conception the fetus is able to respond to sound.

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  • Teratology - The field of study that investigates the causes of birth defects.

  • Teratogen - Any agent that causes a birth defect.

  • Numerous teratogens exist, thus almost every fetus is exposed to at least some.

  • It may take a long time for the effects of a teratogen to show up.

  • Only about half of all potential effects appear at birth.

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Sensitivity during Organogenesis

  • The probability of a structural defect is greatest during organogenesis.

  • 15 - 25 days after conception, the brain is most vulnerable.

  • 24 - 40 days after conception, the eyes are most vulnerable.

  • 20 - 40 days after conception, the heart is most vulnerable.

  • 24 - 36 days after conception, the legs are most vulnerable.

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Sensitivity during the Fetal Period

  • Exposure is less likely to cause anatomical defects.

  • Exposure is more likely to stunt growth.

  • Exposure is more likely to create problems in organ functioning.

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Prescription and Nonprescription Drugs

Both can have possible effects on the fetus.

A tragic example is with the tranquilizer thalidomide, prescribed in the early 1960s.

Mothers do not have to be chronic drug users for the fetus to be harmed.

Taking the wrong drug at the wrong time is enough to physically handicap offspring for life.

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Antibiotics (streptomycin, tetracycline)

Prescription Drugs that Can Function as Teratogens

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Diet Pills



FDA recommends either no caffeine or very little.

Nonprescription Drugs that Can Function as Teratogens

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Heavy Drinking

Moderate Drinking


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Fetal Alcohol Syndrome (FAS) - A cluster of abnormalities that appears in the offspring of mothers who drink alcohol heavily during pregnancy

Facial deformities

Defective limbs, face, and heart

Below average intelligence, with some cases of mental retardation

Adults with FAS found to have a high incidence of mental disorders, such as depression or anxiety

Heavy Drinking during Pregnancy

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Fetal and neonatal deaths are higher among smoking mothers. that appears in the offspring of mothers who drink alcohol heavily during pregnancy

There exists a higher incidence of preterm births and lower birthweights.


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Environmental that appears in the offspring of mothers who drink alcohol heavily during pregnancyHazards

Radiation: nuclear environments, X-rays, computer monitors

Chemicals: carbon monoxide, mercury, lead, pesticides, PCBs

Heat: saunas, hot tubs

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Infectious Diseases that appears in the offspring of mothers who drink alcohol heavily during pregnancy


Emotional States and Stress

Maternal Age


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Mother’s stress can be transmitted to the fetus. that appears in the offspring of mothers who drink alcohol heavily during pregnancy

When a pregnant woman experiences intense fears, anxieties, and other emotions, physiological changes occur.

These affect the fetus through, for example, restricting blood flow to the uterine area depriving the fetus of adequate oxygen.

Effects of Stress on Pregnancy

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Maternal Age that appears in the offspring of mothers who drink alcohol heavily during pregnancy


The Thirties and Beyond

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The risk of Down Syndrome increases after the mother reaches age 30.

Women have more difficulty getting pregnant after the age of 30.

As women remain active, exercise regularly, and are careful about their nutrition, their reproductive systems may remain healthier at older ages.

The Thirties and Beyond

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Men’s exposure to lead, radiation, certain pesticides, and petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

When fathers have a diet low in vitamin C, their offspring have a higher risk of birth defects and cancer.

Fathers’ smoking during pregnancy may lead to lower birthweight and potential for their offspring developing cancer.

Older fathers may place their offspring at risk for certain birth defects, such as Down syndrome and dwarfism.

Paternal Factors

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The Birth Process petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • Stages of Birth

  • The Fetus/Newborn Transition

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The First Stage of Birth petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • This is the longest of the three stages, lasting an average of 12-24 hours.

  • Uterine contractions are 15-20 minutes apart and last up to 1 minute.

  • Contractions cause cervix to stretch and open.

  • Contractions get closer together as the stage progresses.

  • By the end of this stage the cervix is dilated to about 10 cm.

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The Second Stage of Birth petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • This stage begins when the baby’s head starts to move through the cervix and the birth canal.

  • It terminates when the baby completely emerges from the mother’s body.

  • This stage lasts about one and a half hours, and involves the mother bearing down to push the baby out.

  • Contractions come about every minute and last about a minute.

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The Third Stage of Birth petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • This stage is called “afterbirth” and lasts only minutes.

  • It involves the detachment and expulsion of the placenta, umbilical cord, and other membranes.

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The Fetus/Newborn Transition petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • Being born involves considerable stress for the baby.

  • Anoxia (the condition in which the fetus/newborn has an insufficient supply of oxygen) can cause brain damage, and is a concern if delivery takes too long.

  • After the umbilical cord is cut, 25 million air sacs in the lungs must fill with air.

  • The newborn’s bloodstream is redirected through the lungs and to all parts of the body.

  • The baby is born with a protective covering of skin grease called vernix caseosa which is cleaned off.

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The baby's experience of birth petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • Otto Rank (1884-1937): Birth trauma, rather than the Oedipus complex: central position in the causation of psychoneurosis.

  • Hugo Lagercrantz and Theodore Slotkin (1986): As the birth process begins, a surge in the production of adrenaline and other stress hormones protect him/her from adverse conditions.

  • Lagercrantz and Slotkin point out that infants delivered by cesarean section often have difficulty breathing.

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Cesarean Delivery petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • The baby is removed from the mother’s uterus through an incision made in her abdomen.

  • Usually performed if the baby is in a breech position, causing the baby’s buttocks to emerge from the vagina first.

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Measures of Neonatal Health and Responsiveness petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • The Apgar Scale

  • The Brazelton Neonatal Behavioral Assessment Scale

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The Apgar Scale petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • A method widely used to assess the health of newborns at 1 and 5 minutes after birth.

  • It evaluates infants’

    • heart rate

    • respiratory effort

    • muscle tone

    • body color

    • reflex irritability

  • Obstetrician or nurse assesses the newborn and gives a score of 0, 1, or 2 on each item.

  • A score of 7-10 is good, 5 indicates possible developmental difficulties, 3 or below signals an emergency.

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The Brazelton Neonatal Behavioral Assessment Scale petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • Performed within 24-36 hours after birth to evaluate neurological development, reflexes, and reactions to people.

  • The newborn is rated on each of 27 items, contributing to four categories: physiological, motoric, state, and interaction.

  • Babies are also given global classification such as “worrisome,” “normal,” “superior.”

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Parent-child relationship petrochemicals may cause abnormalities in sperm that lead to miscarriage or disease.

  • Bonding is the occurrence of close contact between parents and newborn in the period shortly after birth.

  • Research supports the importance of bonding, but challenges the significance of the first few days of life as a critical period.