Week 4 Flashcards
Biology of Behaviour
First Dichotomy
Physiological or psychological ?
First Dichotomy
Physiological or psychological ?
Cartesian dualism – 2 types of stuff
Physical matter which obeys the laws of nature (body)
Mind which controls behaviour – separate, not physical, no natural laws (soul, self, spirit)
Now – mostly behaviour has a physiological basis (brain)
Damage or stimulation to parts of the brain can produce complex psychological changes
Some nonhuman species now shown to possess abilities once considered purely human “mind” stuff
But … still many feel that some aspect of being human transcends the physical brain
Biology of Behaviour
Second Dichotomy
Nature or Nurture?
Nurture – John Watson
“Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select—doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors. (1930)”
Nature – instinctive behaviours
Flawed question - interactions
Nature
Genes drive neural development
Nurture
Environment influences neural development
Interactions
Environment modifies gene expression – epigenetics
Behaviour driven by the current situation
Experience depends on behaviour
Most adaptive behaviours succeed influencing the gene pool of subsequent generations
Biology of Behaviour
Behaviour is physiological – a biological trait
Current behaviour from complex interactions: Genes Development Past environment (evolution) Past experience (genes and function) Current environment
Mendelian Genetics
Offspring share traits with parents – how are these traits passed on?
Experiments on peas - quantitative experiments not just breeding
Looked at dichotomous traits (2 versions – round/wrinkled pea; green/yellow pea; purple/white flower; standard/dwarf plant)
First establish true breeding varieties – plants that only produce progeny like themselves when allowed to self pollinate –> P1 generation
Then breed parents with different traits –> F1 generation
Then crossbreed F1 –> F2 generation
Transmission genetics – statistical rules governing transmission of hereditary elements one gen to next
Parents true breeding
F1 only 1 kind
F2 mixed in 3 to 1 ratio
Two factors account for the inheritance of dichotomous traits – e.g. a brown seed factor and a white seed factor (i.e. genes - different versions are referred to as alleles)
One allele (Dominant) dominates the other (Recessive)
An organism receives (at random) one gene from each parent
Genotype – the genetic makeup (e.g. 1 brown gene and one white gene)
Phenotype – the expressed or observable trait (e.g. brown seeds – which could be either brown/white genotype or brown/brown)
Molecular Genetics
Mendel’s “factors” are genes – lengths of DNA that code for proteins
Genes reside on chromosomes – long lengths of DNA that contain many genes (and other stuff – promoters, enhancers, inhibitors)
Chromosomes come in pairs (and therefore so do genes)
Humans – 23 pairs – 1 pair from each parent
22 pairs are autosomal chromosomes
1 pair sex chromosomes (XX=F; XY=M)
Chromosome
Gene
DNA
Central Dogma
Flow of genetic information
The version of a gene (allele) determines the form of the protein
Proteins may be structural elements, enzymes, signalling elements replication DNA->DNA DNA Polymerase transcription DNA->RNA RNA Polymerase translation RNA->Protein Ribosome
Meiosis and Variation
chromosomes line up parallel with each other, replicate their genetic material and one chromosome crosses over the other, the crossed over chromosomes break apart at the crossover
therefore shuffling genetic material
First source of variation – different functioning alleles in the population
During replication things can go wrong
Small changes – SNPs – single base pair change
More complex changes – small or large deletions or additions
Whole genome duplications
Sometimes fatal
Sometimes produces slightly modified proteins
Sometimes produces extra genes that are free to evolve further
Molecular Genetics
Central Dogma
Flow of genetic information
The version of a gene (allele) determines the form of the protein
Proteins
Early neural development
Synapse formation and maintenance
NT manufacture
NT receptors
NT transporters
Brain expresses more genes than any other organ
Within the brain, different cell populations express different groups of genes
Nature versus Nurture
Many traits (phenotypes) are polygenic (exceptions e.g. Huntington’s Disease)
Especially true for complex traits like intelligence or personality
Many genotypes influence the likelihood of a particular phenotype – typically not all or none (exceptions e.g. Huntington’s, Down Syndrome)
Often interested more in the genetics underlying variations in a trait rather than the trait itself (e.g. intelligence)
Heritability is a statistic
Heritability
Estimate of the proportion of variability in a given study on a particular trait as a result of genetic variation across individuals in that study
Heritability estimates tell us about the contribution of genetic differences to phenotypic differences among participants
It does not tell us anything about the relative contribution of genes and environment/experience to the development of individuals
In a sample with low environmental variation, contribution of genetic variation may be over-estimated (e.g. upper-middle class American households are environmentally very similar)
In Western samples, complex psychological traits all have heritability estimates somewhere between 40% and 80% percent.
Twin Studies
The main tool for assessing the relative contributions of genetics and environment on psychological traits has been to study monozygotic and dizygotic twins.
Minnesota Study of Twins Reared Apart
59 pairs of monozygotic twins (100% genes shared)
47 pairs of dizygotic twins (on average 50% genes shared)
Ages from 19 - 68
50 hours of testing on each participant (including personality, interests, and attitudes)
Results:
MZ twins were more similar on all psychological dimensions than DZ twins
Regardless of whether they were raised in the same or different household
Jim Twins
MZ twins adopted at the age of four weeks
Both of the adopting couples named their son James
Both married to Bettys and divorced from Lindas
One named first son James Alan, the other named first son James Allan
Both twins have an adopted brother whose name is Larry
Both named their pet dog “Toy”
Both had law-enforcement training and been a part-time deputy sheriff
Each did poorly in spelling and well in math
Each did carpentry, mechanical drawing, and block lettering
Each vacation in Florida in the same three-block-long beach area
Both twins began suffering from tension headaches at eighteen, gained ten pounds at the same time, and are six feet tall and 180 pounds
Down Syndrome
Trisomy 21 – extra copy of chromosome 21
A genetic condition but outcomes depend on environment
Intellectual disability – level varies
DSCAM – a gene on chromosome 21 that encodes a signalling molecule (Down Syndrome Cell Adhesion Molecule)
Expressed in the developing nervous system – over-expressed in DS
Developing neurons – axons need to find the right target
DSCAMs facilitate attraction/repulsion
Influences nervous system development
Alzheimer’s Disease
APOE gene (Chr19) codes for apolipoprotein E
APOE transports lipoproteins, fat soluble vitamins and cholesterol
Expressed in the brain by astrocytes (mostly) and microglia
3 major alleles – E2 , E3 , E4
Allele: General: AD: Effect
APOE2: 8%: 4%: Protective
APOEE3: 78%: 59%: Normal
APOE4: 14%: 37%: Risk
APOE is the most significant genetic risk factor for late onset AD
Inherit an increased risk – not the disease
Relative to the prevalent E3/E3 (i.e. homozygous) genotype
one copy of the E4 allele have an 3.7- fold increase in risk for developing AD
two copies of E4 have a 12-fold increase in risk for developing AD
Role in the brain not clear – synaptogenesis and synaptic maintenance, role in neuronal sprouting after injury
Effect may be due to loss of protective function or gain of toxic function
Correlation between Aβ plaque density and E4 allele in AD autopsy
Increased Aβ production?
Decreased Aβ clearance?
Aβ interferes with normal APOE function?
Intelligence
Selective breeding of “Maze-Bright” and “Maze-Dull” rats
Train a large mixed group to run a complex maze
Breed best performers and worst performers – 21 generations
Cross fostering control to rule out learning
Found to differ on many behavioural traits
Superior maze learners not more intelligent but less fearful
Not adaptive in natural environments
Turkheimer et al. (2003) reported IQ heritability estimates for two SES groups
The heritability estimate for High SES subjects was 70%
However for low SES subjects, the estimate was just 10%
One can inherit genes for strong intelligence but the potential is not realized in an impoverished environment
Evolution
Evolution by natural selection – Darwin
All life is related
Diversity of life is due to descent with modification by natural selection
Survival of the fittest – fittest means most successful at surviving and passing on genes
Adaptive traits survive and spread in a population
Requires variation
When selection is strong, evolution can be fast
Note 1
Darwin not the first to suggest that species evolve
First to compile a large body of evidence
Documented fossil record
Described structural similarities among living species
Noted changes brought about by selective breeding
First to suggest a mechanism - natural selection
Note 2
Darwin not the last word on evolution
Science has progressed and developed massively in 150 years
Modern synthesis – Darwinian evolution by natural selection PLUS genetics
First Mendelian inheritance then modern molecular genetics
Function is the driver of evolution
Successive elaborations of the basic plan – evolution is a tinkerer
First variation - selection from the current pool of alleles
Second variation – new changes due to mutation – from SNPs to whole genome duplications
Primate Evolution
We are not descended from chimps!!
Humans and chimps have a common ancestor
Gene-Culture Co-evolution
Cultural processes can change the selective environment and thereby affect which genotypes survive and reproduce
Lactase persistence and dairying - trait mainly identified in dairying-practising or pastoralist populations
Age estimates in terms of the antiquity of LP alleles coincide with those for the origins of animal domestication and the cultural practice of dairying.
Two contrasting theories
The culture-historical hypothesis - LP developed, and was consequently selected, after milk production and dairy consumption spread
Reverse-cause hypothesis - only populations whose frequency of LP was high enough adopted dairying
Benefits – caloric, vitamin D (correlation with latitude in Europe)
Stone tools?
Social behaviours?
Hidden Benefits
Why do recessive genes that cause serious disease persist?
Sickle cell anaemia
Autosomal recessive
Not enough healthy red blood cells to carry adequate oxygen
Anaemia, pain, swelling, infections, delayed growth, vision problems
No cure
The average life expectancy in the developed world is 40 to 60
Pre-development – likely early death
High incidence in regions with a history of malaria
Heterozygotes – healthy but carry the disease
Heterozygotes – protection from malaria – still contract but much less severe
Selection
Similar for CF and cholera?
Evolution is a Tinkerer
Evolution of the vertebrate eye
Darwin
“To suppose that the eye, with all its inimitable contrivances… could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree… “
“Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist… and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.”
But, the retina is wired up backwards
Not sure why – could be random and when it happened it wasn’t much of an issue
Much tinkering since to manage
Recurrent Laryngeal Nerve
Branch of the vagus nerve supplying muscles of the larynx
Recurrent Laryngeal Nerve
In fish, 6 gill slits are each supplied by a nerve and an artery
Early mammal embryo has this same layout
In mammals the heart drops and the neck extends
RLN got caught on the wrong side
Much easier to incrementally add length than redesign
Evolution
Evolution does not proceed in a single line
Evolution is not always slow and gradual
1% of all known species are alive today
Evolution is a tinkerer (e.g. the human eye)
Not all existing adaptations evolved for their current function
Similar traits do not necessarily have the same evolutionary origins – convergent evolution
Homologous versus Analogous
(Possible) Evolution of the Brain
Early steps – sponges – responsive contractile cells without neurons
Jellyfish and molluscs – intercellular conduction – steps to a real nervous system
Chordates – simple worms (amphioxus) dorsal nerve cord above the notochord – essentially brain stem and spinal cord
Elaboration of the neural tube at head
Primary vesicles expand
Diencephalon develops
Cerebral hemispheres
Driven by behavioural demands
Most basic behaviours for survival and reproduction:
approach/avoid
orient towards/away
explore/forage/seek
Interface with outside world (sensory/motor)
Interface with the inside world
Evolve goal directed activities and hierarchies
Cognitive abilities to anticipate and plan
Functional adaptations drive particular expansions
Evolution of the Human Brain
Early research focussed on size
Later, brain weight as a proportion of total body weight
Now we consider the evolution of different brain regions
Consider the brain stem and cortex separately
In the course of its evolution, the human brain has increased in size, mainly the cortex, accompanied by an increase in the number of convolutions.
Evolution of Behaviour
Behaviour is a product of the brain
Behaviour is a trait that can be selected for
Selection of behaviour drives evolutionary changes in the brain
Behaviours that are adaptive are selected for
Social Dominance
Males of some species – hierarchy of social dominance through combative encounters
Males ranked based on success rate
Hierarchy reduces conflict since lower learn to avoid or submit to higher - Most fighting at the top end
Dominant copulate more
Males: dominance means access to females for reproduction.
Females: dominance means access to food and resources (e.g. chimpanzees maintain access to productive foraging areas)
Evolutionary Psychology
Understand human behaviour by considering pressures that led to evolution of behaviour
E.g. mate bonding – pair bonding v promiscuity
Just so stories for many behaviours
Need predictions to test
Evolution of Language
Communication – transfer of information
Animals have vocalisation and rudimentary communication
Language – complex, structured, flexible, symbolic, recursive, nuanced, broad
Language is a uniquely human trait – less spectrum of abilities and more step change
Genetics of Language
British family “KE”
Several generations affected by severe language impairment - developmental verbal dyspraxia
The affected KE family members had
impaired at receptive vocabulary
impaired at receptive grammar
impaired on a word and nonword repetition tests
impaired at past tense production
linguistic deficiency also in reading and writing.
lower mean nonverbal IQ
Autosomal dominant inheritance pattern
1998, disorder was linked to a small segment of chromosome 7 - SPCH1
Then CS - unrelated person with similar language impairment had a chromosomal translocation involving the SPCH1 interval
2001, a gene called FOXP2 (on the SPCH1 interval) was found to underlie the inherited speech and language disorder.
FOXP2
The FOXP2 gene provides instructions for making a protein - forkhead box P2
Transcription factor - controls the activity of other genes (possibly 100s)
Active in several tissues, including the brain, before and after birth.
Brain development - neuron growth
Synaptic transmission and plasticity
Soft-tissue formation and development
Essential for the normal development of speech and language (neural and physical)
Evolution of FOXP2
FOXP2 highly conserved across mammals
BUT – 2 changes in humans since chimps
Share with Neanderthals and Denisovans so at least 400,000 years ago
Inserted human or chimp FOXP2 into human brain cells
Human increased the expression of 61 genes and decreased the expression of 51 genes
Bats
Various bat species share a high degree of variation in the FOXP2 gene
Closely related bats, with comparable ultrasonic capabilities, tended to have the same changes but not shared with more distantly related bats or bats that don’t depend on echolocation.
Some of the bats had the same mutation that in humans is associated with language disorders.
Orangutans
FOXP2 mutation in Sumatran orangutans compared to Bornean
Sumatran more sociable
Differ in vocal repertoire and pitch frequency of vocalizations
Sumatran individuals are more avid oral tool
FOXP2 gene is a key part of human evolution
Language didn’t evolve from scratch - tinkerer
Depended on genetic pathways present in non-verbal ancestors rather than the sudden appearance of some new mechanism
Key Learnings
Nothing in biology (psychology) makes sense except in the light of evolution
Behaviour is physiological and results from complex interactions between genes and environment over time scales ranging from right now to evolutionary history
Genes, chromosomes, genotypes, phenotypes, alleles
Central dogma, mutation and variation
Complex traits are polygenic
Heritability is a statistic
Some brain phenotypes – Downs, AD, intelligence
Descent with modification by natural selection
Function is the driver of evolution – adaptive traits survive
Evolution is a tinkerer
Gene-culture co-evolution: lactase persistence
Persistence of deleterious recessives – SCA
Brain evolution – not just about size
Evolution of language
