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Chapter 3

Chapter 3- Evolution, Heredity, and Behaviour.doc

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University of Toronto Scarborough
Steve Joordens

Chapter 3- Evolution, Heredity, and Behaviour The Development of Evolutionary Theory • Charles Darwin argued that over time, organisms originate and become adapted to their environments by biological means Biological evolution- changes that take place in the genetic and physical characteristics of a population or group of organisms over time (Darwin) • Primary explanation of the origin of life • Behavioural differences among organisms corresponds to genetic and other biological differences Adaptive significance- the effectiveness of behaviour in helping organisms to adapt to changing environmental conditions Ultimate causes- evolutionary conditions that have slowly shaped the behaviour of a species over generations • “To come to an end” of behaviour Proximate causes- immediate environmental events and conditions that affect behaviour • An complete understanding any behaviour requires to understand the past and present conditions that influence it Culture- the sum of socially transmitted knowledge, customs, and behaviour patterns common to a particular group of people The Voyage of the Beagle • Charles Darwin met Captain Robert Fitz Roy, who wanted an unpaid naturalist and travelling companion during a 5-year voyage on the HMS Beagle to the coast of South America and to make hydrographic measurements worldwide • He spent most of his time collecting creatures and objects, which were later examined by other naturalists all over Europe • Believed in creationism The Origin of Species Artificial selection- a procedure in which certain animals are deliberately mated to produce offspring that possess desirable characteristics • People select which animals will and will not breed based on specific, desirable characteristics of those animals Natural selection- the consequence of the fact, because there are physical and behavioural differences among organisms, they reproduce differentially. 1 • Within a given population, some animals (the survivors) will produce more offspring than will other animals • Any animal that possesses a characteristic that helps it to survive or adapt to changes in its environment is likely to live longer and to produce more offspring than are animals that don’t have this characteristics • Darwin came to this realization in September 1838, but didn’t publish his theory until 20 years later because he wanted evidence and proof that his theory was correct Natural Selection • Ernst Mayr has suggested that Darwin’s immense contribution to modern thinking about evolution can be traced to 4 insights: 1. The species are not fixed, but change over time 2. Evolution is a branching process, all species descend from a single common ancestor 3. Evolution is continuous, with gradual changes 4. Evolution is based on natural selection  Individuals within a population show variability in heritable behavioural and physical characteristics  The capacity of the environment to sustain a population of any species is limited, producing competition • With those 2 factors meant that those individual with the population with characteristics that compete better are more likely to survive, reproduce, and appear in the next generation Reproductive success- the number of viable offspring an individual produces relative to the number of viable offspring produced by other members of the same species Variation Variation- the differences found across individuals of any given species in terms of their genetic, biological (size, strength, physiology), and psychological (intelligence, sociability, behaviour) characteristics • Genotype- an organism’s genetic makeup • Phenotype- the outward expression of an organism’s genotype (physical characteristics and behaviour) • Every individual’s phenotype is produced by the interaction of its genotype with the environment o Genotype determines how much the environment can influence an organism’s development and behaviour • Although evolution occurs over the long run, natural selection can produce important changes in the short run 2 • Phenotypic variation can produce important selective advantages that affect survival Competition Competition- a striving or vying with others who share the same ecological niche for food, mates, and territory • Also occurs between species when members of different species compete for similar ecological resources • Allow only the best-adapted phenotypes and their corresponding genotypes to survive • If there is no competition, fitness would not happen in “survival of the fittest” Heredity and Genetics Genetics- the study of the genetic makeup of organisms and how it influences their physical and behavioural characteristics • The study of structure and functions of genes, how they are transmitted from one generation to another, and how they operate it Heredity- the traits and tendencies inherited from a person’s parents and other biological ancestors • Charles Darwin knew that individual differences occurred within a given species and that those differences were related to natural selections, but didn’t know how adaptations were passed from parent to offspring or why differences among offspring occurred • Gregor Mendal demonstrated how traits of pea plants could be transmitted from one generation to the other and explained the source of the variation of inherited traits • Genetics help provide both proximal and ultimate explanations in psychological processes Basic Principles of Genetics Deoxyribonucleic acid (DNA) - the DNA structure resembles that of a twisted ladder, where strands of sugar and phosphates are connected by rungs made from nucleotide molecules of adenine, thymine, guanine, and cytosine • James Watson discovered that DNA is configured like a twisted ladder: the sugar and phosphate form the sides and the four nucleotides form the rungs Gene- small units of DNA that direct the synthesis of proteins and enzymes • The location of a particular sequence of nucleotides along the DNA molecules Genome- the total set of genetic material of an organism 3 • Contains 24 different DNA molecules in women and 25 different DNA molecules in men • 30,000 to 40,000 genes within the human genome Genes as “Recipes” for Protein Synthesis • Proteins are strings of amino acids, arranged in a chain whose order is specified by the way the nucleotides adenine, thymine, guanine, and cytosine are linked together on the DNA molecule • A sequence of 3 nucleotides corresponds to a particular amino acid • Combining the proteins necessary to create and develop physiological structures and for behaviour- how those structures might function in response to environmental stimulation • No gene for behaviour, only for the physical structures and physiological processes that are related to behaviour Enzymes- proteins that regulate the structure of bodily cells and the processes occurring within those cells (proteins that increase the rate of chemical reactions in bodily cells) • Faulty gene may contain instructions for synthesis of faulty enzymes, which produces serious physiological and behavioural problems • Large segments of the DNA molecule consisting of so-called “junk” DNA is not involved in the direct synthesis of proteins (non-coding DNA) Chromosomes and Meiosis Chromosomes- threadlike structures in the nuclei of living cells that contains genes • Each set of chromosomes contains a different DNA molecule and a different sequence of genes • 23 chromosomes from each parent (46 individual chromosomes) • 22 of these pairs of chromosomes, the 2 DNA molecules are of matching types and the remaining pair are sex chromosomes Sex chromosomes- the chromosomes that contain the instructional code for the development of male or female characteristics • In females, the 2 sex chromosomes are matching DNA molecules (X chromosomes) • In males, the 2 sex chromosomes are different DNA molecules (X and Y chromosomes) • Males genome have one more DNA molecule than female genome • The chromosomes that are not sex chromosomes are autosomes Autosomes- the chromosomes that are not sex chromosomes 4 NOTE: 23 pairs of chromosomes (22 pairs of autosomes and 1 pair of sex chromosomes) • Sperm and ovum differ from the other bodily cells: o Sperm and ova contain only one member of each chromosomes pair o Some of the genetic information on one member of a pair has been exchanged with the information on the other member • The sperm and ovum are produce by meiosis Meiosis- the form of cell division by which new sperm and ova are formed • The chromosomes within the cell are randomly rearranged so that new sperm and ova contain 23 individual chromosomes, or half of those found in other bodily cells 23 • A single individual can produce 2 or 8,388,608 different ova or sperm • Identical twins [monozygotic (MZ) twins] occur when a fertilized ovum divides, giving rise to two identical individuals • Fraternal twins [dizygotic (DZ) twins] occur when a woman produces 2 ova, both of which are fertilized by different sperm Dominant and Recessive Traits Alleles- alternative forms of the same gene • Homozygous- same yolk (same eye colour) • Heterozygous- different yolk (different eye colour) Dominant trait- the trait that is exhibited when an individual possesses heterozygous alleles Recessive trait- a trait that occurs only when it is expressed by homozygous alleles Polygenic control- influenced by many pairs of genes, not just a single pair The Importance of Genetic Diversity • Yeast and fungi reproduce asexually • Nurseries often reproduce plants and trees through an asexual process called grafting • Majority of species reproduce sexually because the sexual reproduction increases a species’ ability to adapt to environmental changes o This leads to genetic diversity because there are 2 different copies of the DNA molecule in the child’s genome o Genetically diverse species have a better chance of adapting to a changing environment because some members may have genes, 5 that manufactures proteins, which enables them to survive in the new environment • Natural selections can favour species that reproduce sexually because of the adaptive value of genetic diversity Influences of Gender on Heredity • The simple pattern of inheritance that is appropriate for traits coded by single genes on the autosomes Hemophilia- an increased tendency to bleed from even minor injuries • A recessive trait caused by a gene on the X chromosomes that fails to produce a protein for normal blooding clotting • Females have 2 X chromosomes, but they can have normal blood clotting if only one carries an allele for hemophilia • Males have 1 X chromosomes from their mothers, so if the gene for blood clotting carries on this chromosomes is faulty, they develop hemophilia • Sex-linked gene resides only on the sex chromosomes • Sex-influenced gene express themselves in both sexes, although the phenotype appears more frequently in 1 sex than the other Mutations and Chromosomal Aberrations Mutations- accidental alternations in the DNA code within a single gene • Can be either spontaneous, occurring naturally, or the result of environmental factors (Ex: exposure to high-energy radiation) Chromosomal aberration- the rearrangement of genes within chromosomes or a change in the total number of chromosomes Cri-du-chat syndrome- infants who gastrointestinal and cardiac problems, have severe problems in mental functioning, and make crying sounds resembling a cat’s meowing • Behaviour that has a genetic basis can often be modified to some extent through training or experience • Partial deletion of the genetic material in chromosome #5 Genetic Disorders • Lethal genes are usually recessive traits and when a child inherits one, along with a healthy gene, the destructive effects of the lethal gene are not expressed • May lead a normal healthy life or die at any time during the life span Down syndrome- a geneticstisorder caused by a chromosomal aberration resulting in an extra 21 chromosome 6 • Show impairments in physical, psychomotor, and cognitive development • Frequency of Down syndrome increases with the age of the mother or father Huntington’s disease- a genetic disorder caused by a dominant lethal gene in which a person’s experiences slow but progressive mental and physical deterioration • Between 30-40 years • Death occurs 5-15 years after onset • Since age of onset is long after puberty, this lethal gene can be passed from parent to child before the parent even knows that they have the gene Phenylketonuria (PKU) – a genetic disorder caused by a particular pair of homozygous recessive genes and characterized by the inability to break down phenylalanine, an amino acid found in many high- protein foods • The resulting high blood levels of phenylalanine cause mental retardation • Responsible for synthesis of a faulty enzyme • Infants are tested after birth Heredity and Behaviour Genetics • Humans differ from other primates in that we are genetically much less diverse • Environment and genetics make us different • Heredity or the environment will depend on specifying the underlying variability Heritability- the amount of variability in a given trait in a given population at a given time due to genetic factors, whether some traits can pass on via the genes • The more that a trait in a given population is influenced by genetic factors, the greater its heritability • Heritability doesn’t apply to individuals, its pertains only to the variation of a trait in a specific population • Inheritance- the tendency of a given trait to be passed from parent to each offspring Behaviour genetics- the study of genetic infl
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