Week 4

Question 1

Biology of Behaviour
First Dichotomy
Physiological or psychological ?

Answer 1

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

Question 2

Biology of Behaviour
Second Dichotomy
Nature or Nurture?

Answer 2

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

Question 3

Nature

Answer 3

Genes drive neural development

Question 4

Nurture

Answer 4

Environment influences neural development

Question 5

Interactions

Answer 5

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

Question 6

Biology of Behaviour

Behaviour is physiological – a biological trait

Answer 6

Current behaviour from complex interactions:
Genes
Development
Past environment (evolution)
Past experience (genes and function)
Current environment

Question 7

Mendelian Genetics

Answer 7

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)

Question 8

Molecular Genetics

Answer 8

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

Question 9

Meiosis and Variation

Answer 9

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

Question 10

Molecular Genetics

Central Dogma

Answer 10

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

Question 11

Nature versus Nurture

Answer 11

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

Question 12

Heritability

Answer 12

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.

Question 13

Twin Studies

Answer 13

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

Question 14

Jim Twins

Answer 14

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

Question 15

Down Syndrome

Answer 15

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

Question 16

Alzheimer’s Disease

Answer 16

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?

Question 17

Intelligence

Answer 17

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

Question 18

Evolution

Answer 18

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

Question 19

Primate Evolution

Answer 19

We are not descended from chimps!!

Humans and chimps have a common ancestor

Question 20

Gene-Culture Co-evolution

Answer 20

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?

Question 21

Hidden Benefits

Why do recessive genes that cause serious disease persist?

Answer 21

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?

Question 22

Evolution is a Tinkerer

Evolution of the vertebrate eye

Answer 22

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

Question 23

Evolution

Answer 23

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

Question 24

(Possible) Evolution of the Brain

Answer 24

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

Question 25

Evolution of the Human Brain

Answer 25

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.

Question 26

Evolution of Behaviour

Answer 26

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

Question 27

Social Dominance

Answer 27

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)

Question 28

Evolutionary Psychology

Answer 28

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

Question 29

Evolution of Language

Answer 29

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

Question 30

Genetics of Language

Answer 30

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.

Question 31

FOXP2

Answer 31

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)

Question 32

Evolution of FOXP2

Answer 32

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

Question 33

Key Learnings

Answer 33

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