A Biological Basis of Behavior

• The Biological Approach toBehavior• Biological explanations of behavior raise theissue of the relationship between mental activityand the brain also know as the “mind-body” or“mind-brain problem”• The “mind-brain problem” has a variety ofexplanations

• The Biological Approach toBehavior• Biological psychology: the study of thephysiological, evolutionary and developmentalmechanisms of behavior and experience• A strong emphasis is placed upon brainfunctioning

• The Biological Approach toBehavior (cont’d.)• Brain functioning can be explained at a moremicroscopic level in terms of neuron and glia activity• Neurons and glia somehow produce an enormouswealth of behavior and experience

• Biological Explanations ofBehavior• Biological explanations of behavior fall into fourcategories:– Physiological: relates a behavior to theactivity of the brain and other organs– Ontogenetic: describes the development ofa structure or behavior– Evolutionary: reconstructs evolutionaryhistory of a behavior or structure– Functional: describes why a structure orbehavior evolved as it did

• Genetics and Behavior• Both genes and environment interact to shapehuman behavior• The fundamental issue is how much a role eachfactor plays in shaping human behaviors– Examples: psychological disorders,weight gain, personality, sexualorientation

• Mendelian Genetics• 19th century monk Gregor Mendel demonstratedthat inheritance occurs through genes• Genes are aligned along chromosomes (strandsof genes) and come in pairs• A gene is a portion of a chromosome and iscomposed of deoxyribonucleic acid (DNA)• DNA serves as a model for the synthesis ofribonucleic acid (RNA)

• Mendelian Genetics(cont’d.)• RNA is a single strand chemical that can serve as atemplate/ model for the synthesis of proteins• Proteins determine the development of the bodyby:• Forming part of the structure of thebody• Serving as enzymes, biologicalcatalysts that regulate chemicalreactions in the body

• Mendelian Genetics(cont’d.)• Homozygous, for, a gene means that a personhas an identical pair of genes on the twochromosomes• Heterozygous, for a gene, means that a personhas an unmatched pair of genes on the twochromosomes

• Mendelian Genetics(cont’d.)• Genes are either dominant, recessive, orintermediate– Examples: eye color, ability to tastePTC• A dominant gene shows a strong effect in eitherthe homozygous or heterozygous condition• A recessive gene shows its effect only in thehomozygous condition

• Mendelian Genetics(cont’d.)• Examples such as PTC and hair color can bemisleading– Implies that a single genecombination completely controls acharacteristic, but this is not true• Some genes are only expressed partly: in somecells and not others or only under certaincircumstances

• Types of genes include:– Autosomal genes: all other genesexcept for sex- linked genes– Sex-linked genes: genes located onthe sex chromosomes• In mammals, the sex chromosomes aredesignated X & Y– Females have two X chromosomes(XX)– Males have an X and a Ychromosome (XY)

• During reproduction:– Females contribute an X chromosome– Males contribute either an X or a Ychromosome that determines the sex ofthe child• If an X chromosome is contributed by the male, theoffspring is female• If a Y chromosome is contributed by the male, theoffspring will be male

X X

XX XY

Y

XY XX

• Mendelian Genetics(cont’d.)• The human Y chromosome has genes for 27 proteins• The human X chromosome has genes forapproximately 1500 proteins• Thus, sex-linked genes usually refer to X-linkedgenes: e.g., red-green color deficiency)• Sex-limited genes are genes that are present in bothsexes but mainly have an effect on one sex (chesthair, breast size, etc.)

• Genes change in several ways:– Mutation: a heritable change in a DNAmolecule– Microduplication/microdeletion: part of achromosome that might appear oncemight appear twice or not at all– Example: some researchers believeschizophrenia might be a result ofmicroduplications and microdeletions ofbrain-relevant genes

• Mendelian Genetics(cont’d.)• Epigenetics: a field that is concerned with changesin gene expression without the modification of theDNA sequence• Some genes are active only at a certain point inone’s life, a certain time of day, etc.• Changes in gene expression are central to learningand memory• Epigenetic differences are a likely explanation fordifferences between monozygotic “identical” twins

• Mendelian Genetics(cont’d.)• What you do at any moment not only affects you now,but produces epigenetic effects that alter geneexpressions for a longer period of time• Experiences alter the activity of genes –• *foods that we eat• *stress

• Heredity and Environment• Almost all behaviors have both a geneticcomponent and an environmental component• Researchers study monozygotic (“from oneegg”) and fraternal (“from two eggs”) twins toinfer contributions of heredity and environment• Researchers also study adopted children andtheir resemblance to their biological parents toinfer hereditary influences

• Heredity and Environment(cont’d.)• Heritability refers to how much characteristicsdepend on genetic differences• Researchers have found evidence for heritabilityin almost every behavior they have tested• Heritability of a certain trait is specific to a givenpopulation• Strong environmental influences may causegenetic influences to have less of an effect

• Heredity and Environment(cont’d.)• Traits with a strong hereditary influence can bymodified by environmental intervention– e.g., PKU: a genetic inability to metabolizethe amino acid phenylketonuria– Environmental interventions can modifyPKU

• Heredity and Environment(cont’d.)• Genes do not directly produce behaviors• Genes produce proteins that increase theprobability that a behavior will develop undercertain circumstances• Genes can also have an indirect affect– Genes can alter your environment byproducing behaviors or traits that alterhow people in your environment reactto you

• The Evolution of Behavior• Evolution refers to a change in the frequencyof various genes in a population overgenerations• Regardless if helpful or harmful to the species• Evolution attempts to answer two questions:– How did some species evolve?– How do species evolve?

The Evolution of Behavior(cont’d.)

• How species did evolve involves the tentativeconstruction of “evolutionary trees”• How species do evolve rests upon some assumptions:– Offspring generally resemble their parentsfor genetic reasons– Mutations, recombination, andmicroduplications of genes introduce newheritable variations– Certain individuals successfully reproducemore than others do

• Artificial selection refers to choosing individualswith desired traits and making them parents ofthe next generation• According to Darwin, nature also selects, andsuccessful individuals’ genes will be prevalent inlater generations

• Evolutionary psychology focuses upon functionaland evolutionary explanations of how behaviorsevolved– Assumes that behaviors characteristicof a species have arisen throughnatural selection and provide a survivaladvantage• Examples: differences in peripheral/color vision,sleep mechanisms in the brain, eating habits,temperature regulation

• Some behaviors are more debatable regarding theinfluence of natural selection• Examples include:– Life span length– Gender differences in sexual promiscuity– Altruistic behavior: a behavior that benefitssomeone other than the actor• Altruism is hard to find outside of humans

Nature vs Nurture

Biology (genes) vs. Experience

Are you the way you are because you’re born that way? Or is it because of the environment you’re raised

• http://www.youtube.com/watch?v=W4N-7AlzK7s

• http://www.youtube.com/watch?v=vHrmiy4W9C0

• A gene only spreads if individuals with itreproduce more than individuals without it• A gene that benefits the species but not theindividual dies out with that individual• Group selection is a controversial hypothesis that states that altruistic groups survive better than less cooperative ones• Kin selection is the favored explanation: selection for a gene that benefit’s the individual’s relatives

• Reciprocal altruism is the idea that individualshelp those that will return the favor• Building a reputation for helpfulness only worksif others are willing to cooperate with you

• Animal research is an important source ofinformation for biological psychology but remainsa highly controversial topic• Animal research varies on the amount of stressand/ or pain that is caused to the animal itself

• Reasons for studying animals include:– The underlying mechanisms of behavior aresimilar across species and often easier tostudy in nonhuman species– We are interested in animals for their own sake– What we learn about animals sheds light onhuman evolution– Some experiments cannot use humansbecause of legal or ethical reasons

• Opposition to animal research varies:– “Minimalists” favor firm regulation onresearch and place consideration upon thetype of animal used and the amount ofstress induced– “Abolitionists” maintain that all animals havethe same rights as humans and any use ofanimals is unethical

• Justification for research considers the amount ofbenefit gained compared to the amount of distresscaused to the animal– No clear dividing line exists• Colleges and research institutions in the UnitedStates are required to have an Institutional AnimalCare and Use Committee– Oversees and determine acceptableprocedures