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Biopsych - Evolution and Genetics (Y1) - Coggle Diagram
Biopsych - Evolution and Genetics (Y1)
Theory of evolution - Darwin and Wallace
All lives on the planet each inherit their genetic information from their ancestors
The common ancestor of all species is a very basic simple organism
Only organisms that are fit enough to survive their environment have the chance to pass on their genes to the next generation through natural selection
4 major principles of evolution - required for evolution and variation drives evolution through mutations
Principle of inheritance - physical and behavioural traits are heritable (appearance and personality)
We inherit our physical and behavioural traits from our parents, and pass our own onto the next generation
The reason that biological or behavioural traits get passed to our children is that we given them our genetic codes
Principle of variation - individuals within a species show variation in their traits
Within a species, every individual is different - different appearances, personality and some genes lead to successful adaptation (better chance to survive, get preserved, remain in gene pool)
Inheritance and variation -
Physical traits e.g. hair colour, behavioural or psychological traits such as working or episodic memory capacity and diurnal preference (length of PER3 gene, 4 or 5 sections)
Genetic codes that affect our working memory capacity -
Working memroy refers to the ability to hold information temporarily active in our minds e.g. holding numbers and passcodes
Working memory capacity is associated with the COMT gene
COMT gene also regulates dopamine in prerontal cortex
Different variants of the COMT gene affects PFC dopamine release
Principle of adaption - some variants of genes are more adaptive than other genes, organisms with those adaptive genes can survive better
Principle of time - over time, natural selection results in changes in species, these changes need to take decades, thousands or millions of years to occur, successful variation accumulates over time in a gradual process
Process of human evolution - it began seven million years ago, when the human lineage broke away from the evolution of chimpanzees
There were about 20 early human-related species but nearly all became extinct
Showing traits similar to humans today; larger brain capacities, smaller teeth than apes bipedality and tool use
Brain size and body size - human brain is not the biggest, but the brain-body ratio in humans has the highest ration of brain to body mass
Solution to evolution can be found in 2 ways:
Homologus evolution - organs with similarity due to being derived from a common ancestral structure (divergent evolution) - common ancestor, similar anatomy) - different function
Analogous - evolution - organs with similarity due to performing similar function (convergent evolution) - different anatomy, same function
Natural selection -
Directional selection -> for one extreme trait and against the other extreme
Stabilising selection -> one moderate trait and against both extremes
Diversifying selection -> for both extremes and against moderate traits
The ultimate goal of natural selection -
what exactly does natural selection want to achieve; able to produce most offspring so that genes can be passed on as many as possible
Evolution does not care about individual survival - it cares about the continuation of the species as a whole as on a genetic level, the genetic code wants to survive and so changes to build the best body to accommodate for this
Natural selection strategies (it's more than the genes of individual organisms)
Kin selection - the genes of individuals who are closely related to us
-> People are willing to make sacrifices or to share resources because our relatives share genes with us
-> We want to help our family members so as to support the transmission of family genes, the ultimate motivation behind this is that this helps the extension of the family genes to the next generation
-> Best example - bees in a beehive
Reciprocal altruism -
-> In many situations, we not only support people who are our family members, but also people who are not our relatives
-> Natural selection is also biased towards favouring those species who are willing to reciprocally support one another because this increase the chance of the species surviving as a whole
Social dominance - Males of a species establish a stable hierarchy of social dominance through combatative encounters with other males
Dominant males win against all others in the group and a hierarchy is created
Hostilities diminish following hierarchy establishment
Lower levels are not as recognisable as less conflict happens
Social dominance is important evolution - dominant males often copulate more and are more effective in passing on genes and characteristics to future generations
McCann (1981) - dominance impact on copulation in elephant seals - animals challenge one another and the dominant male accounted for 3% of the copulations whereas the 10th ranked male only accounted for 1%
Dominant females are also more likely to produce healthy offspring who made it to sexual maturity (Pusey et al, 1997)
This is likely due to them having access to better foraging areas due to dominance
Dominance - signal of best genes, deserving of best in community
Courtship display - copulation occurs when the male and female react appropriately to one another's signals of interest
Thought to promote evolution of new species - species are a group of organisms that are reproductively isolated from others
Tend to emerge when a barrier of some sort isolates two populations and they follow different evolutionary pathways as a result and cross fertilisation becomes impossible
Barriers can be geographic, or behavioural - developing different courtship displays can develop a reproductive barrier between themselves and conspecifics (members of the same species) with only suitable courtship changes producing reproduction
Supporting evidence for natural selection / evolution:
Biogeography - studies the distribution of animal species, distribution of marsupials as evidence and localised changes in characteristics due to localised events
Fossils - systematic changes through geographical layers,
dinosaurs in lower levels -> archaeoteryx in younger layers -> birds
Comparative embryology - compare the processes of development across species determine evolutionary similarities:
Most early embryos look similar -> differences between species as they develop
Embryos of organisms sharing a more recent common ancestor have a closer genetic relationship, and so look similar for a longer period
If two animal species look very similar to each other until very late stages of their embryonic development, they are more likely to be close relatives to the evolutionary tree
Molecular biology - we can analyse the degree of similarity between genetic codes of two species
If they are close to each other in evolution -> high degree of similarity
All living organisms share the same building blocks and mechanisms
DNA - genetic material and code, Amino Acids - proteins and characteristics properties
Closely related organisms share more genetic code -> more similar
Selective breeding programs and structural similarties brought about by common ancestry
Most convincing observations from rapid evolution of finches in Galapogos Islands
Evolution through natural selection - those traits associated with reproduction and survival most likely to be passed onto future generations and this natural selection of advantageous gene pools leads to evolutions which make people better adapted to surviving and reproducing in their environment niche
Natural selection - similarity to selective breeding, survival of the fittest
Fitness - ability of an organism to survive and contribute its genes to the next generation
Course of human evolution - evolution of vertebrates
Chordates - first to evolve from complex multicellular water dwelling organisms; animals with dorsal nerve cords (250 million years after 800 million years ago when organisms first developed)
First chordates with spinal bones evolved 25 million years later - vertebrates
7 classes of them today - 3 fish classes, amphibians, reptiles, mammals and birds
Amphibians -
410 million years ago, bony fish ventured out of water, advantages of living in land and water, food sources, and only adult ones can survive on land
Reptiles -
315 million year, evolved from amphibians, first vertebrates to lay shell covered eggs and be covered in dry scales, reducing reliance on water habitats, dry scales reduce water loss, allowing them to live far from water
Evolution of mammals: 225 million years ago, evolved from reptiles during dinosaur era
Species fed young through mammary glands, earning them the name of mamals
Mammals stopped laying eggs and instead nurtured foetuses in the watery environment (duck-billed platypus only one to lay eggs)
Spending the first stage of life in the mother's body proved an advantage for survival value - allowed stability for complex programs of development to unfold
26 orders of mammals - 16 groups of primates, the order we belong too
Apes - evolved from old world monkeys - long arms and grasping hind feet specialised for arboreal (treetop) travel and opposable thumbs - apes can however stand upright and travel that way for short distances
Chimpanzees share 99% of their genes with humans
Emergence of humankind:
Hominins - six subgroups including Australopithecus and Homo
Homo consists of at least 8 species based on fossil record, with 7 being extinct
Binomial naming system and levels of classification:
Kingdom - animal
Phylum - chordate
Class - mammal
Order - primate
Family - Hominin
Genus - homo
Species - sapiens
Evidence of human population is sparse - only have incomplete fossils in some areas, including Ethiopia, with have shown our progression through brain size, upright posture and opposable thumbs
Human evolution: evolution does not proceed in a single line, it is instead a dense bush
Humans have little reason to claim evolutionary supremacy
Evolution is slow and gradual - rapid change from changes to environment or adaptive genetic mutations
Few products of evolution have survived (only 1% of known species left)
Evolution does not progress to preordained perfection, not all existing behaviours are adaptive, and improvements are not perfect
Exaptations - evolved to serve one function and later co-opted to serve another
Similarities among species do not mean common ancestors - homologous and analogous structures
Evolution of human brain - brain weight as a percentage of body mass is a better measure of intelligence
Brain stem has grown to regulate reflex activities critical for survival, whereas cerebrum is involved in more complex adaptive processes such as learning, perception and motivation
Brain increased in size during evolution - most in cerebrum, most other animals have a brain stem of similar ratio, but not cerebrum
Increase in number of convolutions (brain folds) - increased the surface area of the cerebral cortex and outermost layer of cerebral tissue
Fundamental similarities in brains of all species - all brains are constructed of many neurons and neural structures are usually in the same locations in the brains of related species
Genetics
Genotype - (genotype of the organism is its complete set of genetic materials proteins) inside the chromosomes, there's a double helix of DNA which consists of 4 proteins
Phenotype - observable physical appearance of measurable psychological traits
DNA -
-> Is inside the nucleus which encodes genetic info
-> Two stranded double helix
-> Horizontal bars - four types of protein pairs (A-T, C-G)
-> Discovered in 1953 by Crick et al
Chromosomes -
-> During reproduction, DNA is copied / replicated from one generation to the next generation almost errorlessly
-> 22 pairs of non-sex chromosomes
-> 1 pair of sex chromosomes
-> Determine genetic sex - XY - male, XX - female
Mendel's law of inheritance -
Dominant alleles which lead to the appearance that we have, which is represented with upper case letters
There are also recessive alleles which are only encoded hiddenly and not expressed as phenotypes, represented using lower case letters
4 combinations of the parent's alleles so that for this pair of father and mother, there are 4 different outcomes
If there is one dominant, that is the gene expressed
Two recessive is the only way this will be expressed
Heterozygous or homozygous pairings - punnett squares represent this
Inheritable disorder via a dominant allele -
-> Huntington's disease - motor system disorder; involuntary jerking or fidgeting movements of the limbs, difficulty in motor control - this disorder is passed on through a dominant allele and caused by the CAG mutation
Inheritable disorder via a recessive allele -
-> Inheritable disorder can also be passed on through recessive genes, such as sickle cell anaemia
-> Unlike a dominant allele, a recessive allele does not lead to a disorder but it has the potential to become a disorder when the two parent's recessive alleles combine
Traits are dichotomous - occur in one form, never together - true breeding lines where interbred members always produce offspring with same traits
Mutation - sudden changes in the DNA sequence - when the cell divides or replicates, the replication of DNA is usually correct but sometimes it goes wrong
Three types of genetic mutation - duplication, deletion and inversion
Usually a bad thing -
-> Cancer - apoptosis of the genes are mutated
-> Causes - radiation, viruses, carcinogens etc
Mutations have mostly harmful effects or no effects at all, but sometimes they provide benefits by acting as a trigger of evolution
Chromosomes - reproduction and recombination -
genes located on chromosomes (20th century)
Chromosomes occur in matched pairs and each species has a characteristic number of chromosome pairs - humans have 23
Two genes / alleles that control each trait are situated at the same location, one on each chromosome of a particular pair
Process of cell division that produces gametes - meiosis - chromosomes divide and one of each pair goes to the two gametes that result, and so each one only has half the usual number of chromosomes to form a full set of chromosomes
Random division of pairs of chromosomes is one way meiosis generates genetic diversity
Genetic recombination - during first stage of meiosis, chromosomes line up in pairs, and then the members of each pair cross over one another at random points and exchange sections
Each of the gametes that form a zygote are unique in their genes, as they are spliced together recombinations from parents
All of cell division is mitototic
Structure and replication - each chromosome is a double stranded (double helix) molecule of DNA:
Each strand is a sequence of nucleotide bases attached to a chain of phosphate and deoxyribose - 4 nucleotide bases of adenine, thymine, guanine and cytosine; sequencing of these constitues genetic code
Two strands that compose each chromosome are coiled around one another and bonded together by the attraction of adenine and thymine and guanine for cyotsine
Exact complements
A-G-T-C strand attracted to T-C-A-G strand
Replication - critical process of the DNA molecule, without it mitotic division is not possible:
Two strands of DNA unwind, and the exposed nucleotide bases then attract their complementary bases, and when unwinding is complete two double helix DNA molecules identical to the original are made
Replication does not always go to plan, with some having clinical consequences such as Down Syndrome
In most cases, mutations disappear from the gene pool within a few generations but in some cases, they improve fitness and encourage rapid evolution
Sex chromosomes and sex linked traits
Only chromosomes that do not come in matched pairs
Typical chromosomes which come in matched pairs are called autosomal chromosomes
Two types of sex chromosomes - X and Y, and the two look different and carry different genes
Females - XX, men - XY - traits influenced by genes on the sex chromosomes are refered to as sex linked traits
All sex linked traits are controlled by genes on the X chromosome as the Y chromosome is small and carries very few genes
Traits controlled by gees on the X chromosome occur more frequently i one sex than the other - if the trait is dominant, it occurs more in females, as they have twice the chance of inherting it
Recessive traits occur more in men, as recessive traits will only manifest with two recessive genes on both X chromosomes, whereas the traits are manifested in all males who possess the gene
Recessive sex linked trait - colour blindness being more common in men, rare for women to posses genes for it, Y chromosome is always recessive for colour blindness so only takes one recessive X to produce the trait
Genetic code and gene expression - structural genes contain information necessary for protein synthesis (long amino acid chains that control physiological activities of cells - all cells contain the same genes, but express differently to create different body parts
Stretches of DNA lacking structural genes function as promoters - determine if a structural gene is converted into proteins through gene expression
Control of gene expresion by promoters heavily influences cell maturation and function
Promoters are regulated by being turned up or down - activators (proteins) increase gene expression and repressors (proteins) decrease gene expression
Two phases of gene expression - transcription and translation
Transcription - small section of chromosome of gene unravels and this serves as a template for the transcription of a short strand of ribonucleic acid (RNA) - uracil instead of thymine and has a phosphate and ribose backbone rather than deoxyribose
Messenger RNA is the transcribed RNA that carries the code out of the nucleus of the cell
Translation - mRNA leaves nucleus, attached itself to a ribosome present in the rough endoplasmic reticulum and the ribosome moves along, translating the genetic code as it proceeds
Each group of three consecutive nucleotide bases is a codon - instructs the ribosome to add one of the 20 different amino acids to the protein it constructs
Guanine-guanine-adenine - glycine amino acid added
Each kind of amino acid is carried to the ribosome by transfer RNA - codon is read, attracts transfer RNA molecule attached to amino acid needed and ribosome repeats the process until the protein is completed
Phenylketonuria - single-gene metabolic disorder; easier to understand the genetics of a behavioural disorder than it is to understand the genetics of a behaviour
PKU - neurological disorder caused by one abnormal gene, making it unique as normally they are the result of many genes
High levels of phenylpyruvic acid contributed to the discovery of the disorder - other symptoms include vomiting, seizures, hyperactivity, irritability and brain damage
PKU transmitted by a single gene mutation - recessive and so only in homozygous individuals, lowest in African and Asian Americans than in those of European descent (Bilder et al, 2016)
PKU homozygotes lack phenylalaine hydroxylase, an enzyme required for the conversion of amino acid phenylalanine to tyrosine and so it is accumulates in the body and so dopamine levels remain low as it is syntheised from tyrosine and this causes abnormal brain development
Behavioural systems of PKU result from interaction between genetic and environmental factors - PKU gene and diet
Blood screening in newborn babies allows those with high phenylalanine levels onto special diet that restricts consumption of it and this reduces the amount of it in the body and development of intellectual disability is lessened, but does not prevent subtle cognitive deficits
Timing of treatment is important - only effective in first few weeks of life
Diet relaxed in adulthood
Sensitive period for the trait where diet is effective
Gene-environment interaction
Dichotomies - as humans, we tend to simplify many things:
Historically, we have a tendency to think in overly simple dichotomies
People who take a purely biological approach -> genes, brains and physiological traits
People who take a purely behaviour / learning approach -> learning and experiences
Nature v nurture - strong, partisan debate
Origins of this thinking - Descartes; Cartesian dualism; mind and body are separate entities, and this is what separated human and non-human animals
Issues with dichotomous thinking - two entities in dualism are not entirely separated, as physiological influences psychological and vice versa
Primate species also have some human characteristics
Self awareness is a hallmark of the human mind - Sack (1985) studied a man with asomatognosia, a deficiency of awareness of part's of one's own body, typically involving the left side due to damage in the right frontal and parietal lobes
However, Gallup's 1983 study suggested that chimpanzees also possessed this - they recognised themselves in mirrors after a certain point, and this mirror self recognition test became an indication of self awareness in animals
Nature v nurture runs into difficulty - initially, it was the discovery of other factors such as the foetal environment, nutrition, stress and sensory stimulation shown to be influential
Changed nurture to experience
However, flawed assumption about additive genetics - interaction is better approach
Behaviour is a product of both
Integrative approach - nature and nurture interact
Two extreme views are wrong as each of the factors alone is not sufficient to explain behaviour
Again, in the case of gender, biological factors determine the sex organs a person has, while learning experience can reduce or reinforce one's gender stereotypucal behaviour
The two factors interact with each other, which in turn affect one's temperament / behaviour
Two influential classic studies
Tryon (1940) - bright rats v dull rats - genes important
Before their selective breeding, they tested a large group of rats on a maze task, and they found some rats were smart, some were dull and scores were evenly distributed
Selectively breeding the rats in order to make smart rats smarter, and dull rats duller
After many generations of selective breeding, the two distributions are very separated from each other
Cooper and Zubek, 1958 - Tryon follow up
The environment is restricted, and so the bright and dull rats suffer from the lack of opportunity to play and learn, with no difference between bright or dull rats
When the environment is enriched, both the bright and dull rats benefit from plentiful opportunities to play and learn, with no difference between bright or dull
When the environment is normal, the bright rats outperformed the dull rats by a large margin - huge difference between bright and dull
Proves environment does matter - enriched environment equalised performance despite genetics, and genetics only have a real impact in an unchanged environment, as in a restricted environment they also still under performed despite genetics
Minnesota Study of twins - Bouchard et al, 1990: studied idential and fraternal twins -
Found identical twins to have more similar IQ scores compared to fraternal twins - genetic influences
Within identical twins, kids reared together had more similar IQ than those reared apart, suggesting an environmental influence
Key argument - genetic influences seem to be more important than environmental influences -> nature > nurture
Problems with this study -
even though the twins were raised apart, their environments were still very similar to one another - raised in highly similar foster families, assessed by the social care system, that tended to have similar characteristics
Identical twins - treated more similarly than fraternal twins - both environments and genes make them similar
The researchers of this twin study did not share the raw data of their study for examination (no determination of error or biases)
Meta-analysis of twin studies - Polderman et al, 2015:
In the meta-analysis, they take a higher perspective - they look at the conclusion of each study and average the statistical data across studies
They looked at 2,700 publications, with more than 10 million twin pairs included in their study
Genetic influences account for 49%, and environmental influences account for 51%
It is not nature v nurture - it is nature and nurture as both are equally important
Epigenetics
How does the environment influence genetic expression -
One directional process in which our genes impact our phenotypes - DNA -> RNA -> proteins -> phenotypes
Not all genes are expressed, some are inhibited by environment factors - environmental factors can suppress the expression of a certain section of DNA preventing phenotype expression
Our genes and our environment affect our phenotypes -
Epigenetics - focused on the interaction between genes and environment
Epigenetic research on questions such as - how environment turns off and turns on genes, how we can improve the environment to facilitate gene expression and what kind of environment suppressed or facilitates gene expression
Environment - epigenetic modifications and gene regulation creates phenotype
Genetics - DNA sequence variations leads to gene regulation and phenotypes
Transgenerational epigenetics - examines transmission of experiences via epigenetic mechanisms across generations
How genetic factors and experience interact to direct behavioural ontogeny:
Ontogeny - development over lifespan of individuals
Phylogeny - evolutionary development of species through the ages
Environmental factors that impact the expression of genes -social interaction, diet, medication, tobacco/alcohol, sports and financial stability
Human behaviour is a result of the complex interactions of genes, past experiences and current situations
ACEs can result in epigenetic mechanisms
Some are transgenerational
Study of mechanisms of inheritance other than those mediated by changes to the gene sequence of DNA
Find the purpose of the other 99% of genes that are not structural
Key discoveries - investigations of non gene DNA have identified active areas which control the expression of nearby genes - no junk DNA
Mechanisms that can modulate gene expression have been discoevered - methylation remodelling when methyl group attaches to a DNA molecule at cytosine sites
Histone remodelling - histones (proteins around which DNA is coiled) change their shape and influece the shape of adjacent DNA - remodelling can increase or decrease expression
Epigenome catalogue building - all modifications to DNA within a particular cell type that changes the nucleotide base sequence - 600 cells characterised so far
Some epigenetic effects involve post-transcription alterations to RNA that do not affect the RNA base sequence - paid attention to epigenetic modifications of mRNA and tRNA and this has led to attempts to catalogue epitranscriptomes
Epigenetic mechanisms can be induced by particular experiences
A model of the biology of behaviour - organisms, genetic endownment, a product of their evolution
Its experience
Its perception of the current situation
https://docs.google.com/document/d/1EEsp5B91D28bDyCTxu50Rc0tIy-Tz14OquKHYDwDof8/edit
Development of individuals v development of differences among individuals:
Development of individuals - gene and experience are inseparable, separable in development among individuals
Measured by asking a group of volunteers and ask what proportion of variation among them in some attribute results from genetic differences as opposed to experiential differences
Behavioural geneticists therefore commonly compare MZ and DZ twins to understand genetic influences on traits
Also studying MZ twins reared apart and together can also indicate genetic influence and environmental influence - two kinds of future twin studies
Epigenetic effect twin studies: epigenetic changes triggered by experience and passed onto future generations
Often not studied in humans as it is unethical to create negative experiences
MZ twins provide a method of circumventing this, and so repeated DNA assessment can document epigenetic effects that we develop
Comparison to DZ twins allows understanding of whether the changes are a result of genetic or experiential factors - if epigenetic mechanisms are genetic, patterns would be similar in MZ
Fraga et al, 2005 - found twins are epigenetically indistinguishable in early life, but the differences accumulate with age, suggesting MZ twins are not actually entirely genetically identical as they have different epigenetic changes which alter DNA
Wong et al (2010) - changes in DNA methylation are mainly experential
Epigenetic differences could explain one twin gaining a disease and the other not
Disease discordant MZ twin studies are a powerful approach to understanding the causes and mechanisms of a disease through epigenetic differences
Twin studies of the effects of experience on heritability: Turkheimer et al (2003):
Influence of socio-economic status, two samples of twins from lower class families and middle to high SES
Heritability estimates for intelligence was 70% in middle to high SES, but was only 10% in low SES twins
Intelligence - genes and experience - poverty environments limit opportunities to develop intelligence
Also has implications to intervention programs to help the poor
Human Genome Project
Purpose of compiling a map of the sequence of all 3 billion nucleotide bases that compose human chromomsomes
Motivated by potential medical applications
Developed new techniques for studying DNA, discovered we only have 21,000 structural genes - researchers have a nearly complete map for the entire set of proteins our gees can encode - human proteome
Variations linked to human genome that cause disease have been identified but sorting out the interactions between the genes implicated and experience to cause these diseases