CHAPTER 3: THE EVOLVING MIND- NATURE AND NURTURE INTERWINEDGenes can be turned on and off.The genes that are not turned off are free to produce the proteins needed to build a particular kind of cell.Genes do not just turn on and off as they build a body during development.Your ongoing interaction with the environment can turn genes on or off.FoodSmoking/drinkingStress levelsIdentical twins become less similar as they age.Why do we say nature and nurture are intertwined?Nature- the contributions of heredity to our physical structure and behaviorsNurture- the contributions of environmental factors and experience to our physical structure and behaviors.Francis Galton- described the contrast between heredity and environment as “nature vs. nurture”; Darwin’s cousin; believed that intelligence was largely the result of inheritanceWhat are the building blocks of behavior?Genotype- an individual’s profile of allelesPhenotype- Observable characteristicsEach parent contributes a set of 23 chromosomesGene- Small segment of DNA located in a particular place on a chromosome.Gene expression- The process in which genetic instructions are converted into a feature of aliving cellAllele- one of several different versions of a gene, as in having A, B, or O blood type alleleHomozygous- having two of the same alleles for a geneHeterozygous- having two different alleles for a geneRecessiveness- a feature of an allele that will only produce a phenotype in the homozygous conditionDominance- a feature of an allele that will determine a phenotype in either the homozygousor heterozygous conditionGenetic VariationA single human can produce eggs or sperm with 2^23 different combinations of his or her chromosomesRelatedness- the probability that two people share the same allele from a common ancestorThe chance that you share an allele with one of your parents is one half, as is the chance that you share an allele with a siblingFirst cousins have 1/8 liklihood of sharing an alleleSex chromosomes22 out of the 23 pairs of chromosomes from each parent are perfectly matchedThe X and Y sex chromosomes do not carry the same genesMost of the genes located on the Y chromosome are involved with male fertilitySex linked characteristicsThe X chromosome contains genes that influence a wide variety of characteristics like bloodclotting and the ability to see the colors red and green.Genes responsible for hemophilia, or the failure of blood to clot, and the red-green colorblindness are found on the X chromosome.These are recessive so when women get them they are just carriers and do not experience itA male receiving this X chromosome gene will have the conditionSo, these are much more frequent among malesEpigeneticsDifferent phenotypes can result from the same genotype due to interactions between the organism and the environmentEpigenetics- the study of gene-environment interactions in the production of phenotypesThe environment can determine if and when a particular gene is activatedWhat is the field of behavioral genetics?Behavioral genetics- the scientific field that attempts to identify and understand links between genetics and behaviorHeritability- the statistical likelihood that variations observed in a population are due to geneticsUsually presented as a ratio of the amount of variation observed in a population due to genetics relative to the total amount of variation due to both genetic and environmental influencesIf genes play no part in producing phenotypical differences between individuals, heritability is 0.0Ex. Having a heartIf genes are totally responsible for all phenotypical differences between individuals, heritability is 1.0.Heritability of most human traits is usually between .3 and .6Genes encode for proteins, not behaviorsGenes build proteins that are used to construct brains, and brains may or may not initiate the behavior of drinking alcohol. Genes do not cause but “contribute” to the development and functioning of the nervous systemHow does evolution occur?Evolution- descent with modification from a common ancestorCharles Darwin- proposed that species evolve or change from one form to the next in an orderly manner.Natural selection- the process by which survival and reproduction pressures act to change the frequency of alleles in subsequent generationsGregor Mendel- discovered ways to outline and predict the inheritance of particular traits, like the color of flowers, in his research on pea plants.Mechanisms of EvolutionEvolution can be caused by natural selection but also mutation migration and genetic drift.Mutation- errors that occur when DNA is replicatedMigration- movement to a new locationPhenotypical traits that are advantageous in one environment might be less so in anotherGenetic drift- change in a population’s genes from one generation to the next due to chance or accidentWhen a person has a choice of mates of equal value, he or she will select the one that ”stands out from the crowd”Individuals with blonde hair color, which was different and more rare, might have enjoyed more reproductive success than those with more common, darker hair colors.Rare things tend to be viewed as valuableFitness- the ability of one genotype to reproduce more successfully relative to other genotypesSurvival to adulthoodAbility to find a mateReproductionNatural selection favors the organism with the highest degree of fitness.Adaptation-a change due to a natural selectionBehaviors, such as jumping higher to better avoid a predatorAnatomical features, such as eyes that can see colorAny adaptation that is ‘good enough’ to contribute to the fitness of an organism will carry forward into future generationsAdult human males have about 10 times as much testosterone as adult human females.Men with higher testosterone report having more sex partners and earlier ge at intercourse.High testosterone levels are correlated with lower immune system functioning, making them more vulnerable to disease.Evolution of the Human BrainHominin- species that walked on two feet, had large vrains, and are assumed to be related to modern humansBrains grew rapidly, suggesting that improved intelligence was quickly translated into substantial advantages in survivalAustralopithecines- early tool-using hominins, had brains like modern chimps 400 cubic cm.Homo erectus- a hominin with a brain 700 cubic cmHomo sapiens- modern humans 1400 cubic cm brainsPrimates, elephants, and whales’ brains also grew fast.The major