Trait variation and categorization, basic models of inheritance, and the connection via DNA

the cognitive mechanisms (modules) that constitute the human brain are assumed to have developed via

natural selection

evolutionary theory principles

1. principle of variation

2. principle of inheritance

3. principle of adaptation

4. principle of evolution

principle of variation

individuals within a species show variation in their physical and behavioural traits

principle of inheritance

some of this variation is heritable

principle of adaptation

individuals are in competition with one another for scarce resources and some inherited variations will have survival advantages

principle of evolution

as a consequence of being better adapted to an environment, some individuals will produce more offspring, who will inherit the same advantages (fitness)

sexual selection

creation and maintenance of features essential for attracting the opposite sex and defending one’s status

works together with natural selection

inclusive fitness

characteristics will be selected for that improve the chances of an individual’s genes being passed directly or via relatives

natural selection

the principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations

mutations

random errors in gene replication that lead to a change in the sequence of nucleotides in the genome, resulting in changes in specific gene expression, brain function, and behaviour

adaptive behaviour

an evolutionary adaptation that enhances survival and reproductive success

evolves as natural selection fine-tunes an animal to its environment

adaptive problems

finding a mate, finding food, avoiding predation, fighting off disease

can affect reproductive success (fitness)

can be tackled by adaptive changes in physiology and behaviour

evolutionary psychologists

argue that our psychological mechanisms and the resulting behaviours have also been shaped by evolutionary forces

proximate causation

the immediate psychological, physiological, biochemical, and environmental reasons:

• sensory systems- need to be able to perceive danger

• mechanisms that drive muscles that elicit behaviour- need to be able to contract muscles to run

• cellular activities regulate development- nerve function

ultimate causation

the reason why it increased fitness in the evolutionary past:

• how does the internal machinery work?

• why does machinery work that way?

• is that behaviour an adaptation?

• how does that behaviour allow the individual to survive, find food, find mates, escape predators, communicate?

adaptation

represents a trade-off between different survival and reproductive needs

but environment may alter more rapidly than organism can evolve, so this is not always adaptive in every circumstance

exaptations/co-option

a shift in function of a trait during evolution- features that may once have been adaptive for one function may have changed over time to serve a different function

spandrels

phenotypic charactertistic that is a byproduct of the evolution of another trait, rather than a direct product of adaptive selection

may look like an adaptation but in fact simply design constraints

role of environment in adaptation

interactions with environmental features during development are critical for normal development

input during development may be required in order to activate certain adaptive features

developmental events may channel individuals into one of several different paths

environmental events may disrupt the emergence of an adaptation

evolutionary psychology

the study of the physiological, evolutionary, and developmental mechanisms of behaviour and experience, i.e. the application of Darwinian principles to the understanding of human nature

strong emphasis is placed on brain functioning

biological explanations of behaviour

physiological, ontogenetic, evolutionary, functional

biological explanation of behaviour- physiological

relates a behaviour to the activity of the brain and other organs

biological explanation of behaviour- ontogenetic

describes the development of a structure or behaviour (recapitulates phylogeny)

biological explanation of behaviour- evolutionary

reconstructs evolutionary history of a behaviour

biological explanation of behaviour- functional

describes why a structure or behaviour evolved

biggest increase in brain size of humans

prefrontal cortex, now accounts for 29% of total cortex in humans

prefrontal cortex

plays a central role in forming goals and objectives and then in devising a plan of action required to attain those goals

selects cognitive skills needed to implement the plans, coordinates those skills, and applies them in a correct order

responsible for evaluating our actions as success or failure relative to our intentions

evolutionary psychology limit

deterministic, or ignores the role of the environment in shaping human behaviour

bidirectional view

environment and biological conditions influence each other

evolution gives us bodily structures and biological potentialities but it does not dictate behaviour

individuals create behaviour in the context of culture

function of extended childhood time in humans

allows time to develop a large brain and learn complexity of human society

Mendel

crossed a line bred true for brown seeds with one bred true for white

first generation offspring has all brown seeds

when the first generation were bred, result was ¾ brown and ¼ white seeds

brown was dominant phenotypic trait, appearing in all of the first generation

phenotype

observable traits

genotype

traits present in the genes

what does the nucleus contain?

chromosomes

genes

inherited factors

humans have about 25,000 of them

direct cells to reproduce themselves and to assemble proteins

collaborate with each other and with non-genetic factors inside and outside the body

expression affected by environment

DNA is the same in all _______ cells of an organism

somatic

meiosis

produces four daughter germ cells

involves recombination/crossing over of chromosomes in prophase I

germ cells not clones of the original cell because each gamete has exactly half as many chromosomes as the original cell

mitosis

produces two daughter cells, somatic cells

no recombination/crossing over of chromosomes in prophase

somatic cells are clones of original cell

fertilization

fusing of sperm and egg to create zygote, creates one set of paired chromosomes (23 from each parent)

karyotype

number and appearance of chromosomes in the nucleus of a eukaryotic cell

sources of variability in human reproduction

combining genes of both parents (chromosomes in zygote not exact copies)

identical/monozygotic twins

fraternal/dizygotic twins

gene mutations (can permanently alter segments of DNA)

chromosomal abnormalities

occur when there is an error in cell division following meiosis or mitosis

caused by a missing, extra, or irregular portion of chromosomal DNA

human behavioural and personality characteristics

observable and measurable components of a person’s phenotype, which is the detectable expression of a person’s genotype interacting with the environment

behaviour genetics

seeks to discover the influence of heredity and environment on individual differences in human traits and development

linkage studies

look for patterns of inheritance of genetic markers in larger families

genetic marker

a segment of DNA that varies among individuals

heritability

the statistical estimate of the proportion of the total variance in some trait that is attributable to genetic differences among individuals within a group

expressed as a proportion, max value is 1

some variable such as height are highly heritable, others are moderately heritable

limitations of heritability

as estimate applies only to a particular group living in a particular environment

estimates do not apply to individuals, only to variations within a group

even highly heritable traits can be modified by the environment

heritability of behaviour estimated in multiple ways:

examining whether children more closely resemble their adoptive or biological parents

comparing monozygotic and diozygotic twins

examining identical twins raised in different households (social environments)

adoption studies

allows researchers to compare correlations between the traits of adopted children and those of their biological and adoptive relatives

these results are used to estimate heritability

twins raised in different environments

identical genes but different environmental factors

any similarities in traits should be primarily genetic and should permit a direct estimate of heritability

shared environmental experiences

siblings common experiences

accounts for little of the variation in children’s personality or interest

• parents personalities

• intellectual orientation

• socioeconomic status

• neighbourhood

non-shared environmental experiences

child’s unique experiences

• within family

• outside family

• not shared by another sibling

• heredity influences this through heredity-environmental correlations

heredity-environment correlations

complex

individuals influence environment, yet individuals inherit environments

genotype-environmental correlations change as children grow

passive genotype environment interaction

parents provide rearing environment

evocative genotype environment interaction

genotype elicits certain types of physical and social environment (good grades)

active genotype environmental interaction

when children seek out compatible and stimulating environments

intelligence quotient

measure of intelligences originally computed by dividing a person’s mental age by their chronological age and multiplying the result by 100

derived from norms provided for standard intelligence tests

genetic influences grow even stronger with age

intelligence scores of identical twins raised together

always more highly correlated (87%) than for fraternal twins

intelligence scores of adopted children

highly correlated with their biological parents

psychiatric diseases

complex diseases that aggregate in families but do not segregate in a simple Mendelian manner

molecular genetic studies have only been able to explain a small fraction of this compared to population estimates which can explain much more

epidemiological studies and psychiatric diseases

have demonstrated correlations between life experiences (perinatal events, socioeconomic status) and psychiatric disease risk but are unable to detect any specific causal environmental hazards

prevalence

measure of the number of cases of a disease in a certain population for a specific period of time

used to refer to how widespread a disease has become

takes into consideration both the number of old and new cases of a disease as well as their duration

incidence

measure of the number of new cases of the disease

rate at which the disease is manifested in a certain population

only takes into consideration the number of new cases

but more reliable in determining risk of a certain disease to a population

complex/multifactorial disorders

no one single genetic cause- likely associated with the effects of multiple genes (polygenic) in combination with lifestyle and environmental factors

tend to run in families, unlike single gene disorders, but they do not have clear-cut patterns of inheritance, so it is difficult to predict a person’s risk of inheriting or passing on these diseases

difficult to treat due to genetic and environmental factors

examples of complex/multifactorial disorders

heart disease, diabetes, Alzheimer’s, autism, parkinson’s, asthma, spina bifida

missing heritability of complex disorders

discrepancy between epidemiological heritability estimates and the proportion of phenotypic variation explained by DNA sequence differences

explanation

• part of heritability being hidden in numerous weakly contributing genetic risk factor patterns of linkage disequilibrium- i.e. nonrandom occurrence of a combination of alleles or genetic markers in a population

• heritability estimates being inflated by epistatic gene interactions- i.e. genes can mask each other’s presence of combine to produce an entirely new trait

other molecular mechanisms involved in major psychosis

passage of epigenetic marks (DNA/histone modification) through germ line

passage of maternal RNA molecules into the embryo

potential passage of prion proteins from parent to offspring

biochemical state of the gametes at the time of conception

transmission of nutrients, bacteria, or antibodies from maternal circulation to that of the offspring

not all traits are equally

heritable or unaffected by shared environments

experiences that hinder cognitive performance

poor prenatal care

malnutrition

exposure to toxins

stressful family circumstances

experiences that enhance cognitive performance

good health care and nutrition

mental enrichment in home and childcare or school