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Chapter 3

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University of Ottawa
Gustavo Gottret

Chapter 3: Biological Beginnings The Evolutionary Perspective Natural Selection and Adaptive Behaviour -natural selection is the evolutionary process that favours individuals of a species that are best adapted to survive and reproduce -Darwin observed that organisms reproduce at rates that would cause enormous increases in the population of most species, and yet populations remain nearly constant -an intense, constant struggle for food, water, and resources must occur among the many young born each generation because many of the young do not survive -those who do survive pass on their genes to the next generation -over many generations, organisms with characteristics needed for survival would compromise a larger percentage of the population of a given species and this could produce a gradual modification of the whole population -if environmental conditions changed, other characteristics might become favoured by natural selection, which would move the process in a different direction -adaptive behaviour promotes an organism's survival in the natural habitat -all organisms must adapt to particular places, climates, food sources, and ways of life -e.g.: attachment is an adaptive behaviour designed by natural selection to ensure an infant's closeness to the caregiver for feeding and protection from danger -e.g.: sickness and aversion to certain foods during pregnancy may enhance the offspring's ability to survive Evolutionary Psychology -evolutionary psychology emphasizes the importance of adaptation, reproduction, and "survival of the fittest" in explaining behaviour -evolution favours organisms that are best adapted to survive and produce in a particular environment -this type of psychology focuses on conditions that allow individuals to survive or cause them to fail -the evolutionary process of natural selection favours behaviours that increase organisms' reproductive success and their ability to pass their genes to the next generation -just as evolution shapes our physical features, it also influences how we make decisions, how aggressive we are, our fears, and our mating patterns - David Buss Evolution and Development -we use concepts of evolutionary psychology to understand human development: 1) An extended juvenile period evolved because humans require time to develop a large brain and learn the complexity of human social communities -humans take longer to become reproductively mature than any other mammal -during this juvenile period, they develop a large brain and the experiences required for mastering the complexities of human society 2) Many aspects of childhood function as preparations for adulthood and were selected over the course of evolution -one example is play; boys in all cultures engage in more rough play than girls, which might prepare them for fighting and hunting as adults -girls engage in play that involves more imitation of parents; this is an evolved tendency that prepares females for becoming primary caregivers for their offspring 3) Some characteristics of childhood were selected because they are adaptive at specific points in development, not because they prepare children for adulthood -e.g.: some aspects of play may function not to prepare us for adulthood, but to help children adapt to their immediate circumstances and help them learn about their current environment 4) Many evolved psychological mechanisms are domain-specific -the mechanisms apply only to a specific aspect of a person's makeup -for example in information processing, the mind is not a general-purpose device that can be applied equally to a vast array of problems -instead, as our ancestors dealt with certain recurring problem, specialized modules evolved that process information related to those problems (i.e.: modules for physical knowledge, mathematical knowledge, and a module for language) -in this view, infants enter the world prepared to process and learn some information more readily than others and these preparations serve as the foundation for social and cognitive development -e.g.: infants are biologically prepared to learn the sounds that are part of human language 5) Evolved mechanisms are not always adaptive in contemporary society -some behaviours that were adaptive for our ancestors may not serve us well today -e.g.: the food-scarce environment of our ancestors may have led to humans' tendency to gorge when food is available and to crave high-caloric foods Evolution and Life-Span Development -why do humans live so long after viable reproduction? -maybe evolution favoured longevity because the work and presence of social elders improves the survival rates of babies -Paul Baltes: "the benefits of evolutionary selection decrease with age" -natural selection has not influenced the prevalence of conditions that mostly affect older adults, but rather does for those that are tied to reproductive fitness earlier in the life-span -as older adults weaken biologically, they need culture-based resources -e.g.: for cognitive skills to continue into old age at comparable levels of performance to earlier in adulthood, they need cognitive support and training are needed -e.g.: Alzheimer's Disease -does not appear before age 70 -if he disease struck 20 year olds, natural selection would have eliminated it long ago -this disease may emerge layer in life because evolutionary pressures based on reproductive fitness do not select against individuals prone to them (the benefits of evolutionary selection decrease with age) Evaluating Evolutionary Psychology Bandura: -acknowledges the influence of evolution on human adaptation and change -rejects "one-sided evolutionism" which sees social behaviour as a product of evolved biology -an alternative is the bi-directional view which says that the environment and biological conditions influence each other -evolutionary pressures create changes in biological structures for the use of tools, which enables organisms to manipulate, alter, and construct new environment conditions -increasingly complex environmental innovations produce selection pressures for the evolution of specialized biological systems such as consciousness, thought, and language -human evolution gave us bodily structures and biological potentials, not behavioural dictates -the pace of social change demonstrates that biology does not permit a wide range of possibilities Gould: -biology allows a broad range of cultural possibilities Dobzhansky: -human species has been selected for the ability to learn and their plasticity; for the capacity to adapt to diverse contexts and NOT for biologically-fixed behaviour Genetic Foundations -our genetic codes are alike in that they all contain the human genetic code -the human genetic code allows only human egg to be fertilized by human sperm -genetic code is found in every cell of our body The Collaborative Gene -the nucleus of each human cell contains chromosomes which are threadlike structures that are made up of DNA -DNA is a complex molecule that has a double helix shape and contains genetic information -genes are the units of hereditary information -are short segments composed of DNA -genes act as a blueprint for cells to reproduce themselves and manufacture the proteins that maintain life -each gene has its own designated location on a particular chromosome -the Human Genome Project is attempting to map the human genome, which is the complete set of developmental instructions for creating proteins that initiate the making of a human organism -there are about 20 500 human genes -proteins are the building blocks of cells -humans have far more proteins than they have genes so there cannot be a one-to- one correspondence between genes and protein -the human genome consists of genes that collaborate both with each other and with non-genetic factors inside and outside the body -the activity of genes (genetic expression) is affected by their environment -e.g.: hormones influence genetic expression and environmental conditions such as light, nutrition, etc. influence the flow of hormone -a single gene is rarely the source of a protein's genetic information, much less of an inherited trait Mitosis, Meiosis, and Fertilization 1) Mitosis -the division of autosomal (body) cells -requires the chromosome to be duplicated before the cell divides so that each new cell will have the correct number of chromosomes -for humans, the number of chromosomes is 22 and 1 more pair of sex chromosomes -during mitosis, the cell's nucleus and its chromosomes duplicate and the cell divides -2 new cells are formed and contain the same DNA as the original cell and is arranged in the same 23 pairs of chromosomes 2) Meiosis -a cell of the testes or ovaries duplicates its chromosomes but then divides twice to form 4 cells -each new cell has half the genetic material of the parent cell -at the end, each egg or sperm has 23 unpaired chromosomes; the cells are known as gametes 3) Fertilization -the process by which an egg and a sperm fuse to create a single cell known as a zygote -in the zygote, the 23 unpaired chromosomes from the sperm and the 23 from the egg combine to form 23 pairs of chromosomes -each parent contributes half of the offspring's genetic material - XX sex chromosome in females; XY sex chromosome in males Sources of Variability -during the formation of sperm and egg in meiosis, the members of each pair of chromosomes are separated -before the pairs separate, pieces of the 2 chromosomes in each pair are exchanged, creating new combinations of genes on each chromosome -when chromosomes from the mother's egg and the father's sperm are brought together in the zygote, this is a unique combination of genes -identical twins (monozygotic twins) develop from a single zygote that splits into 2 genetically identical replicas -fraternal twins (dizygotic twins) develop from separate eggs and separate sperm, making them genetically no more similar than ordinary siblings -another source of variability comes from DNA -a mistake by cellular machinery or damage from an environmental agent such as radiation may produce a mutated gene (a permanently altered segment of DNA) -a genotype is the person's genetic heritage; the actual genetic material -a phenotype is the way an individual's genotype is expressed in observed and measurable characteristics -e.g.: physical traits like height, weight, eye colour, skin pigmentation -e.g.: psychological traits like intelligence, creativity, personality, etc. -for each genotype, a range of phenotypes can be expressed -e.g.: a person can be born with genes that yield a genotype for an advanced level of analytical intelligence; the phenotype will be dependent upon many environmental factors being present like parental encouragement, appropriate schooling, and proper nutrition -the range over which that environment can influence a phenotype is called the reaction range Genetic Principles 1) Dominant-Recessive Genes -a recessive gene only exerts its influence if both genes of a pair are recessive -e.g.: brown eyes, far-sightedness, and dimples are dominant over blue eyes, near-sightedness, and freckles 2) Sex-Linked Genes -most mutated genes are recessive -when a mutated gene is carried on the X chromosome, the result is X-linked inheritance -if there a disease-creating gene on the X chromosome, makes have no backup copy to counter the harmful genes and therefore, there may be an X-linked disease -females have a 2nd X chromosome which is likely to be unchanged -most individuals who have X-linked diseases are males -females who have a changed copy of the X gene are known as carriers and show no sign of the X-linked disease -e.g.: hemophilia and fragile X syndrome 3) Genetic Imprinting -occurs when genes have differing effects depending on whether they are inherited from the mother or the father -a chemical process silences one member of the gene pair -e.g.: Bechwith-Wiedemann syndrome, Wilms tumour -polygenic inheritance is the genetic principle that many genes can interact to produce a particular characteristic -traits produced by this mixing of genes are said to be polygenically determined Chromosome and Gene-Linked Variation 1) Chromosome Variations -when gametes are formed, the 46 chromosomes do not always divide evenly a) Down Syndrome -extra or altered chromosome 21 -physical variations; mild to severe retardation -requires surgery to correct heart and intestinal anomalies b) Klinefelter Syndrome -extra X chromosome -causes physical variations c) Fragile X Syndrome -variation in the X chromosome -intellectual disabilities, learning disabilities, short attention span d) Turner Syndrome -a missing X chromosome in females -intellectual disability and sexual underdevelopment e) XYY Syndrome -causes above average height 2) Gene-Linked Variations -variations can result from harmful genes -the 22 other pairs of chromosomes are known as autosomes and account for most genetic disorders -in autosomal-dominant patterns, one parent will usually be affected with the disorder -if only one parent has the dominant gene, then half the children will exhibit the disorder -if both parents have the gene, then all children will have the disorder -e.g.: achondroplasia (bone growth disorder), hereditary colon cancer, neruofibromatosis I -in autosomal-recessive patterns, if both parents are carriers but not affected by the disorder, each offspring will have a 1 in 4 chance of being affected -e.g.: phenylketonuria, sickle-cell anemia, Tay-Sachs disease, cystic fibrosis 1) Cystic Fibrosis -glandular dysfunction that interferes with mucous production -breathing and digestion are hampered -requires physical and oxygen therapy, synthetic enzymes, antibiotics 2) Diabetes -body does not produce enough insulin, causing abnormal metabolism of sugar 3) Hemophilia -delayed blood clotting causes internal and external bleeding 4) Huntington Disease -CNS deteriorates, resulting in problems in muscle coordination and mental deterioration -appears at around age 35; death results 10 to 20 years later 5) Phenylketonuria (PKU) -metabolic disorder that may cause mental retardation if untreated 6) Sickle-Cell Anemia -blood disorder that limits the body's oxygen supply -can cause joint swelling, heart and kidney failure 7) Spina Bifida -neural tube disorder tha
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