We Are All Alike and We Are All Different –Bacterial DNA in Human Genomes
Nature vs Nurture Confusion Nature vs Nurture (genes vs environment) is a false dichotomy All mature traits are a combination of genes and environment –for example: Language Binocular Vision Aggressive behavior Sexual orientation "To ask what's more important, nature or nurture, is like asking what's more important to the area of a rectangle, its length or its width." attributed to Donald HebbDonald Hebb length and width can be changed independently of each other but they always are dependent on each other
Figure 1.9 Identical Twins but Nonidentical Brains and Behavior
Nature vs Nurture Confusion What is Nature? –inborn or inherent qualities often called instinct or innate –biologically determined primarily by genetic What is Nurture? –rearing, upbringing, training, education, especially for children –although any environmental experience Separate concepts that should not be pitted against each other –Nature and Nurture work together –Predisposition a genetic effect which influences the phenotype of an organism but which can be modified by the environmental conditions
Nature and Nurture Interaction (Genotype) (Environment) Phenotype –Genes you are born with –Environment you are exposed to –Both are always present –This is not an additive process Genes + environment is incorrect Interaction of genes and environment Phenotype is an emergent property of genes and environment * No complete explanation for how this interaction works
Nature and Nurture Interaction Relationship between genes and behavior –Genes are expressed to produce proteins –Proteins provide the structure and chemistry of neurons –Neurons are connected into brain circuits –Brain Circuits process information for sensory, perception, cognition, behavior and so on –There are no genes with a specific behavioral function A Gene for playing the piano A Gene for playing basketball A Gene for math ability –However, genes do influence all of these to some extent
Gene Expression Information from a gene is used in the synthesis of functional proteins or RNA Regulated during transcription and translation –regulated by other genes which can activate or repress environmental signals such as sights, sounds, odors, tastes –controls structure and function of the neuron which allows an organism to adjust to an environment i.e. learning –basis for neuronal differentiation during development –can serve as a substrate for evolutionary change Mutations to regulatory genes will change the regulation of gene expression which can have a profound effect on development and function
Appendix Figure A.2 DNA Makes RNA, and RNA makes Protein Regulation of transcription Environmental signals which trigger changes to molecular biology of the neuron
Nature Nurture Interaction Environmental signals (Experience) –odor of food, sound of a predator or sight of a mate –Information processed through the nervous system –molecular biology of brain circuits is modified (neuroplasticity) long lasting changes to the chemistry and anatomy of neurons. Genes expression plays a crucial role in this process –Genes code for proteins –Genes are signaled by the environment to express proteins –This is the basis of memory formation which we will cover in chapter 17
Role of environment in cognitive abilities environmental enrichment increasing the levels of sensory, cognitive and motor stimulation induce modifications in brain structure and function –increasing the birth and maturation of new neurons into functional circuits –enhancing the expression of molecules involved in neuronal signaling –promoting synaptic plasticity.
Nature Nurture Interaction Intelligence Example –Low genetic heritability for sense of humor, food preferences, political attitude, religious affiliation –However intelligence (g factor) is distinctly influenced by genetic heritability –But there are no specific genes for intelligence, maybe for brain size and certainly for number of neurons –Twin studies indicate 50% genetic influence –Environmental factors must be the other 50% Although this changes across your life span with more environmental influence at a young age and less as you get older So the nature - nurture interaction changes with development
Role of endophenotypes in mental illness Endophenotypes are subcomponents or parts of a phenotype –Sequence variations within specific genes related to specific neural system dysfunctions –Can be used as biological markers –They do not directly cause the disease –But represent the individual susceptibility to the disease –Such as sensory gating ratios in Schizophrenia Environmental factors such as stressor interact with the endophenotypes
Nature Nurture Interaction Autism example Historical opinion on the etiology of autism – (1) that autism is caused by some specific genetic abnormality, spawning a search for the “autism gene”, –(2) that autism is the result of some specific environmental factor or condition, including a “lack of maternal warmth” Genetic: 60% concordance in monozygotic twins –identified genetic factors explain only a small Environment: deficits in social perception –Children with reduced social cognitive development –Parents may also have a reduced social perception
Nature Nurture Interaction Reading Example Learning to read is a combination of nature and nurture. –Letters are environmental stimuli that change the brain circuits –because of gene expression which is neuroplasticity –other examples such as binocular vision, recognizing objects and faces. Neuronal recycling hypothesis –Brain circuits in the inferior ventral temporal cortex evolved to process information for object and face recognition –There is enough plasticity to also learn to recognize letters. But then letters are objects Writing is a cultural invention. Letter shapes are constrained by brain circuits –Invention of writing is grounded in basic object recognition Letter shapes are based on common features in objects (mostly) This is true to some extent for all cultural inventions Innate brain circuit anatomy constrains culture On the other hand cultural information changes the anatomy of the brain circuits So it is nature – nurture interaction all the way down
Determinism Determinism is the philosophical proposition that every event is causally determined by an unbroken chain of prior occurrences. If all processes in the world were due to the mechanical interplay of atoms so that the physical matter of the universe operates according to a set of fixed, knowable laws. Genetic determinism: genes determine a physical or behavioral phenotype. Environmental determinism: experience determines a physical or behavioral phenotype
Determinism and Free Will “Free will is the belief that human behavior is an expression of personal choice YOU, a self with a central command center, are in charge.’ “Sense of self provides an illusion that we are agents acting of our own free will, making important choices.” “Puncturing this illusionary bubble of a single willing self is difficult” “What on earth do humans want to be free from? Indeed, what does free will even mean?” Gazzaniga, Michael S. Who's in Charge?: Free Will and the Science of the Brain (p. 105-106). Harper Collins, Inc..