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Lecture 3

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Lecture 3

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  1. Lecture 3 Heredity and Environment Prenatal Development Birth

  2. Heredity and environment The case of intelligence

  3. 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.

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

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. W. Stern (1871-1938) • Mental age should be divided by chronological age  Intelligence quotient (IQ).

  11. 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.

  12. USA • 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.

  13. 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

  14. Problems • 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).

  15. 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.

  16. 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.

  17. 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."

  18. 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.

  19. Intelligence • 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.

  20. 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

  21. 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.

  22. 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.

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

  24. 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.

  25. The Course of Prenatal Development • The Germinal Period • The Embryonic Period • The Fetal Period

  26. 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.

  27. 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

  28. 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

  29. 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

  30. 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

  31. 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

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

  33. The Fetal Period The period that begins 2 months after conception and lasts, on average, 7 months

  34. 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.

  35. 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.

  36. The End of the Fifth Month • The fetus is 30 cm long.

  37. The End of the Sixth Month • The fetus is approximately 35 cm long. • A grasping reflex is present.

  38. The End of the Seventh Month • The fetus is 40 cm long. • The fetus is very active.

  39. 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.

  40. Prenatal Diagnostic Tests • Maternal Blood Test • Ultrasound Sonography • Amniocentesis • Chorionic Villi Sampling

  41. Amniocentesis • 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)

  42. 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

  43. 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.

  44. Teratology • 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.

  45. 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.

  46. 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.

  47. 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.

  48. Antibiotics (streptomycin, tetracycline) Prescription Drugs that Can Function as Teratogens

  49. Diet Pills Aspirin Caffeine FDA recommends either no caffeine or very little. Nonprescription Drugs that Can Function as Teratogens

  50. Heavy Drinking Moderate Drinking Alcohol