Chapter 2: Biological Beginnings

1. Life-Span Development Twelfth Edition Chapter 2: Biological Beginnings ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

2. Natural Selection ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Natural Selection: an evolutionary process by which those individuals of a species that are best adapted are the ones that survive and reproduce • Based on Darwin’s theory • Survival characteristics are passed on in genes • Can produce a gradual modification of the population over many generations • Survival characteristics may change based on environmental conditions • Adaptive Behavior: behavior that promotes an organism’s survival in the natural habitat

3. Evolutionary Psychology ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Evolutionary Psychology: emphasizes the importance of adaptation, reproduction, and “survival of the fittest” in shaping behavior • Fit: the ability to bear offspring that survive long enough to bear offspring of their own • Natural selection favors behaviors that increase reproductive success • David Buss is a very influential evolutionary psychologist

4. Evolutionary Developmental Psychology ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Extended childhood period allows time to develop a large brain and learn complexity of human society • Many evolved psychological mechanisms are domain-specific • Information processing • Evolved mechanisms are not always adaptive in contemporary society

5. Brain Sizes of Various Primates and Humans in Relation to Length of Juvenile Period ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

6. Evolution and Life-Span Development ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Why do humans live so long after reproduction? • Perhaps older people improve the survival rate of babies • Paul Baltes: benefits of evolutionary selection decrease with age • Natural selection is tied to reproductive fitness • Does not weed out harmful conditions that appear among older adults • Increases our need for culture

7. Evaluating Evolutionary Psychology ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Evolutionary psychology approach is just one theory of many • It has its limitations and weaknesses, and its critics • Bidirectional view: environmental and biological conditions influence each other • Evolution gives us bodily structures and biological potentialities, but it does not dictate behavior • People create behavior in the context of culture

8. Genetic Foundations ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Human life begins as a single cell • Nucleus of each cell contains chromosomes • Chromosomes: thread-like structures made up of DNA • DNA: a complex double-helix molecule that contains genetic information • Genes: units of hereditary information in each chromosome • Genes direct cells to reproduce themselves and to assemble proteins • Proteins: building blocks of cells and regulators that direct the body’s processes

9. Genetic Foundations ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Each gene has its own unique location on a particular chromosome • Human Genome Project attempted to map the human genome • Genome: complete set of developmental instructions for the making of a human organism • Results indicated that humans have about 20,000 to 22,000 genes • Humans have far more proteins than they have genes • Genes collaborate with each other and with non-genetic factors inside and outside the body • Genetic expression is affected by the environment

10. Genetic Foundations ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

11. Genes and Chromosomes ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • All cells in the human body (except sperm and egg) have 46 chromosomes arranged in 23 pairs • Mitosis: reproduction of cells • Nucleus (including chromosomes) duplicate, and the cell divides • Meiosis: cell division that forms sperm and eggs (gametes) • Each cell divides twice, forming four cells with 23 unpaired chromosomes

12. Genes and Chromosomes ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Fertilization: fusing of sperm and egg to create a zygote • Creates one set of paired chromosomes (23 from each parent) • Child’s sex determined by 23rd pair of chromosomes • XX = female, XY = male

13. The Genetic Difference Between Males and Females ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

14. Sources of Variability ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Combining genes of both parents increases genetic variability • Chromosomes in zygote are not exact copies • Identical (monozygotic) twins develop from a single zygote that splits into two • Fraternal (dizygotic) twins develop from separate eggs and sperm • Gene mutations can permanently alter segments of DNA

15. Genetic Principles ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Genotype: a person’s genetic material • Phenotype: observable characteristics • A range of phenotypes can be expressed for each genotype • Dominant-Recessive Genes Principle: a dominant gene always exerts its effects, overriding the potential influence of the recessive gene • A recessive gene only exerts influence if both genes in a pair are recessive

16. Genetic Principles ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Sex-linked genes: • X-linked inheritance occurs when a mutated gene is carried on the X chromosome • More likely to affect males than females • Females have a second X chromosome, which is likely to be unchanged • Men do not have a second X chromosome to counteract the effect • Females are still carriers • Examples: hemophilia and fragile-X syndrome

17. Genetic Principles ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Genetic Imprinting: occurs when genes have differing effects depending on whether they are inherited from the mother or the father • Polygenetic Inheritance: characteristics that are determined by the interaction of many different genes • Most characteristics are determined in this manner

18. Chromosomal Abnormalities ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Chromosome abnormalities usually involve the sperm and ovum lacking a normal set of 23 chromosomes • Down syndrome: caused by the presence of an extra copy of chromosome 21 • Sex-linked abnormalities involve the presence of an extra X or Y chromosome (or the absence of one) • Klinefelter syndrome: males born with XXY instead of XY • Fragile X syndrome: occurs more often in males than females; X chromosome constricted or breaks off • Turner syndrome: females born with XO rather than XX, sometimes causing infertility • XYY syndrome: males with extra Y chromosome

19. Chromosomal Abnormalities ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

20. Gene-Linked Abnormalities ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Gene-linked abnormalities are caused by harmful genes • PKU: inability to metabolize phenylalanine • Sickle-cell anemia: impaired red blood cells die more quickly; more often found in African Americans • Other abnormalities: cystic fibrosis, diabetes, spina bifida, Huntington disease, and Tay-Sachs disease

21. Gene-Linked Abnormalities ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

22. Dealing with Genetic Abnormalities ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Every individual carries DNA variations, but most do not display a disorder • Today, many genetic diseases can be detected prior to and immediately after birth • However, knowledge of genetic flaws leads to difficult choices about how to manage such information • Genetic counselors help people make reproductive decisions

23. Prenatal Diagnostic Tests ©2009 The McGraw-Hill Companies, Inc. All rights reserved. Ultrasound Sonography: high-frequency sound waves used to create a visual representation of fetus’s inner structures Fetal MRI: magnetic resonance imaging designed to diagnose fetal malformations Chorionic Villus Sampling: small sample of placenta is removed to detect genetic and chromosomal abnormalities Amniocentesis: samples amniotic fluid to test for chromosomal or metabolic disorders Maternal Blood Screening: identifies pregnancies with elevated risk for certain birth defects

24. Infertility and Reproductive Technology ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Infertility: the inability to conceive a child after 12 months of attempting • In Vitro Fertilization (IVF): egg and sperm are combined in a laboratory dish; fertilized egg is transferred to woman’s uterus • Success depends on woman’s age • Increases risk of multiple births • Higher risk of life-threatening problems • Health risks to mother • Possible psychological effects on children

25. Infertility and Reproductive Technology ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

26. Infertility and Reproductive Technology ©2009 The McGraw-Hill Companies, Inc. All rights reserved.

27. Infertility and Reproductive Technology ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Adoption: an alternative to infertility treatment • Children adopted early in life fare better than children adopted later • Somewhat more likely to experience psychological and school-related problems than non-adopted children • No differences in antisocial behavior or self-esteem • Vast majority of adopted children adjust effectively, and most parents are satisfied with their decision to adopt

28. ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Behavior Genetics: seeks to discover the influence of heredity and environment on individual differences in human traits and development • Twin studies: compare identical (monozygotic) twins with fraternal (dizygotic) twins • Adoption studies: compare the characteristics of adopted children with their adoptive parents and their biological parents • May also compare adopted and biological siblings

29. ©2009 The McGraw-Hill Companies, Inc. All rights reserved. Heredity – Environment Correlations: individuals’ genes may influence the types of environments to which they are exposed

30. Behavioral Genetics ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Shared environmental experiences: siblings’ common experiences • Non-shared environmental experiences: a child’s unique experiences, both within and outside the family • Shared environment accounts for little of the variation in children’s personality or interest • Heredity influences the non-shared environments through heredity–environment correlations

31. The Epigenetic View ©2009 The McGraw-Hill Companies, Inc. All rights reserved. • Epigenetic view: development is an ongoing, bi-directional interchange between heredity and environment • Heredity and environment operate together

32. Conclusions ©2009 The McGraw-Hill Companies, Inc. All rights reserved. The relative contributions of heredity and environment are not additive Complex behaviors have some genetic loading that gives people a propensity for a particular developmental path Our environment is complex, and the interaction of heredity and environment is extensive Much needs to be learned about specific ways in which environment and genetics interact to influence development