Adaptation Flashcards
Outline different levels of adaptation
- homeostasis- up tod ays
- developmental plasticity- days to years
- selections- over generations/ millennia
- genetic, physiological and developmental modes of adaptation can interact
Compare human genetic variation to that of other species
- low in comparison- 0.1% compared to 1% in flies etc
- most variation occurs within population
What is now a prominent force of evolutionary change
- cultural evolution- dominant force of evolutionary change acting on the human body- Lieberman
Outline environmental stressors
- Any challenge to optimal fitness = stress
- Climate
- Diet
- Pathogens, parasites and toxins
- Predation
- Competition for resources
- Competition for mates
Outline now selection acts
- acts on diversity via reproductive fitness
- surviving long enough to reproduce, attracting a mate fertility, and number of offspring contribute to fitness
List the requirements of natural selection
- Heritable variation in the population.
- If it’s not in the genes, can’t select for it
- Differential reproductive success (different variants have different numbers of offspring surviving to reproduce in turn)
Outline the process of adaptation
- occurs via physiological, biochemical or anatomical modifications within a species over several/many generations
- long-term adaptations are the result of genetic changes that increase the individual’s ability to survive and reproduce
- reproductive fitness is the ultimate pay-off
Outline local adaptation
Fan et al (2016):
- local adapations allow global spread
- e.g. MCM6 to acts persistence, APOL1 to Malaria
- Genetic diversity tends to accumulate in populations over time but smaller populations have less diversity as bottlenecks reduce diversity
- Migration (geneflow) reduces diversity and differences between populations
- Selection reduces diversity of target alleles and neighbouring – linked regions
Outline sources of genetic diversity
- somatic mutations- can’t be inherited
- germ lime mutations- acted on my natural selection- in sperm/egg so inherited
- recombination gives diversity without mutation
- Genetic drift, natural selection and migration change allele frequencies over time
Outline phenotypic plasticity
- The ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions
- homeostasis- bodies constantly adapting to regulate blood glucose and oxygen, core body temperature, water volume, blood pressure, chemical levels e.g. sodium/calcium/pottasium ions
- Exercise, training and diet able to influence, but also genetic influences on weight
Outline the influence of genetics on phenotypic plasticity
- different phenotypic possibilities no infinite or same for all people
- depending on environmental inputs, some outcomes more likely than others (Dennett)
- genotype limits extent of phenotypic variation
Outline an example of an adaptive phenotypic trait (mice), and explain plasticity in this trait
Linnen et al, 2009:
- coat colour
- mice in Nabraska adapted to the brighter, sandy soil of the Sand Hills area (not more than 15ky old)
- variation arose from a de novo mutation in the Agouti gene that determines the amount of yellow pigment in the hair- selection acting on advantageous mutation
Plasticity:
- changes in diet (supplementation with methyl donors) silebcxes agouti gene (Waterland & Jirtle, 2003)
- The Avy allele of the Agouti gene has a retrotransposon inserted upstream of the transcription start site of the gene- DNA methylation represses expression leading to healthy brown mice (Pleitropy)
Outline genetic plasticity
- Classical view: you cannot inherit acquired characteristics- genes have no ‘memory’ of the environment or experiences of previous generations
- Methylation in the promotor region of a gene can block transcription factor binding so that the gene cannot be transcribed: it is switched off
- very small, reversible chemical change (not a mutation)
- other kinds of epigenetic changes e.g., histone modifications and expression of some non-coding RNAs that interfere with other coding RNAs
Outline developmental plasticity
- e.g. catch up growth
- can cause cell proliferation and growth and decrease cell senescence
Outline the idea of sensitive periods in plasticity
- have a sensitive period in which take cues from mother and early environment
- this sets developmental plasticity trajectory for rest of life- may or may not be adaptive
- 2 types of plasticity- wither gradual acting which results in form matching function, or brief sensitive period in which developmental repose is adaptive
List different cultural adaptations
- clothing- e.g. thermal from reindeer for cold
- Housing e.g igloo thermodynamic (packed snow mainly trapped air)
- domestication of ruminants early-mid holocene
- agriculture- for abundance from higher yielding crops and animal husbandry, buffering against unpredictable variation in natural resources, and increased fertility- more calories for less effort
- may be maladaptive- foot binding (stopped 1912), corsets, keyboard types based on historical contingency
Outline the issues with the development of agriculture (cultural adaptation)
- Rapid changes outpaced genetic adaptation: mismatch.
- Health consequences - higher morbidity and mortality due
to - Less diverse diet and microbiome: heavy dependence on major crops (35-50% more starch) and local/seasonal water supply: risk of famine and malnutrition.
- Increase in zoonotic diseases, parasites and infectious disease generally due to poor sanitation and overcrowding: e.g., tuberculosis, syphilis, plague.
- Tooth decay due to sugary/abrasive foods.
- Increasingly hierarchical social structure leading to inequalities (poverty), social stress and conflict
Outline the link between agriculture and neolithic expansion
- Quantity vs quality trade off in reproductive fitness may have driven neolithic expansion – as supported by this study of Agta people at different stages of transition from mobile foraging to settled
- Mothers who transition to agriculture have higher reproductive fitness – despite increased disease and mortalit
Outline quality vs quantity trade off in reproduction as a result of agriculture
- more calories in less time- can put more effort into reproduction (increases quantity)
- but more disease/mortality- life history trade off- lower quantity
Outline niche construction
Lewontin, 1983:
- An organism significantly modifies its environmental conditions.
- These changes influence selection pressures on that organism – and/or other organisms.
-This leads to evolutionary changes in the organism(s)
Outline an example of gene-culture co-evolution
Stock & Wells, 2023:
- lactose intolerance
- selected independently in different regions- several alleles associated with lactase persistence
- Chain of influences following niche- constructing practice for dairy farming
- e.g. culture- cattle farming, milk consumption, secondary dairy products and breeding of vary cattle influence genetic factors (lactase persistent allies in humans and dairy cattle allele), echoic influence population growth and dispersal
Outline domestication.
- Domestication syndrome- Floppy ears, Curly tails, Prosocial temperament, Smaller brain
- Craniofacial differences between modern humans and Neanderthals and between dogs and wolves- questions whether humans may have self-domesticated by favouring pro-social behaviour (Theofanopoulou et al, 2017)
Outline fatalities due to extreme heat
- 107 in 2017, 134 30 year average
Outline figures regarding hot environments
- Hottest officially recorded air temp: 56.7 °C (134 ° F) Furness Creek, Death Valley USA, 1913 (58 °C Libya 1922 disputed).
- Ground also Furness Creek, 93.9 °C, 1972
- At least 22 countries > 50 °C
Outline what rate of heat loss in humans depends on
Occurs via evaporation (sweating), depends on:
* Surface area
* Vapour pressure/humidity
* Surface temperature
* Amount of liquid on surface
Outline the sweating response
- occurs when skin temperature exceeds 35 degrees
- can sweat up to 10-12 l/day, up to 2-3 l/hour
- ineffective when humidity exceeds 75%
Outline thermoregulation
- blood and internal temperature increases
- receptors send impulses to hypothalamus
- causes vasodilation in skin blood vessels so more heat is lost across the skin
- sweat glands come more active, increasing evaporative heat loss
- causes a decrease in body temperature
- negative feedback process- physiological response to counteract change in temperature
Outline heat acclimatisation
Périard et al, 2015:
- occurs over 2-10 days
- heart rate decreases
- slight decrease in core temperature
- increase in sweating rate
- increase in plasma volume
- increase in exercise capacity and thermal temperature
- plateau 10-14 days
Outline prevalence of hot and dry weather
- 14.2% Earth’s surface is hot desert
- Over 1 billion people live in desert regions
Outline the extent tie which effects of high heat can be buffered
- cultural buffering e.g. through housing
- Culture can buffer dry heat better than humid heat
Outline cultural buffering in hot and dry environments
Housing adaptations:
- composition and position of walls, roofs and interior functions can be altered
- E.g. Mexican Adobe houses- flat roofs, natural ventilation, reflecting sun, walls with high thermal mass
Outline hot and humid environments
- e.g. tropical rainforests
- Solar radiation restricted by moist air and clouds
- Lower daily temperature variation
- Less convection
- Evaporation slow due to humidity
- Feels hotter due to humidity: 88% in wet season, 77% in ‘dry’
- harder to adapt to as sweating less effective
Outline statistics regrading extreme cold environments
- Coldest officially recorded temp -89.2 C, Antarctica
- Coldest summer -33 °C, Greenland
- Lowest in N Hemisphere - 69.6 °C Greenland
- Coldest city: -62.2 °C Yakutsk, Russia (2023),
- More permanently inhabited: Oymyakon, Russia
Outline physiological consequences of cold environments/hypothermia
- 35- mild hypothermia- shivering, numb hands, reduced manual dexterity
- 33-34- moderate hypothermia- contact shivering, slurred speech, impaired decisions, lack of co-ordination.
- 32- severe hypothermia- shivering fails and stirs, loss of consciousness
- 30- consciousness lost
- 28- death
Outline windchill
- how cold it actually feels on skin when wind is factored in
Outline cultural buffering to extreme cold environments
- Decrease heat loss- cheaper and easier- clothing and housing- avoid wind/water
- Increase heat production: moving/exercise, eating fat/protein, e.g., whale skin and blubber
- E.g. Greenland- consumption of whale blubber steaks, seal meat as protein source (suaasat)
Outline short term physiological responses to cold
- hypothalamus triggers warning mechanisms
- vasoconstriction when skin temp < 35 °C
- hormonal thermogenesis- non-shivering thermogenesis relies on brown fat around major arteries and veins
- shivering increases
- Involuntary shivering begins in the torso then to the limbs- highly effective but limited duration
- Insulative acclimation: enhanced vasoconstriction redistributes blood flow to keep core warm
- core temperature to return it to set point
- this cause hypothalamus to turn off warning mechanisms (negative feedback process)
- less blood flow to brain, higher blood pressure, higher heart rate,
Outline the hunting response
- Alternating vasoconstriction and vasodilation
- Can protect from frostbite but also result in painful swelling
- Affects people working outdoors or handling frozen meat- develops over time so response adapts and sets in earlier
Outline physiological effects of being wet and cold
Thompson & Hayward, 1996:
- Intense shivering attempts to maintain core temp
- Severe peripheral cooling impacts motor and mental behaviour
- Decreased strength and dexterity.
Outline brown fat plasticity
Lee et al, 2014:
* 5 healthy men, 21 yrs
* 4 months in NIH Clinical
Centre, Maryland, USA
* One month (2nd of 4) of night temp 19 °C
* 42% increase in brown fat volume
* 10% increase in fat metabolic activity
* Improved insulin sensitivity
* Returned to baseline at neutral night temp
- depleted after 8 days out of environment- plastic response
- Cold influences thyroid hormone production, e.g., thyroxine which initiates adaptive thermogenesis in BAT
Outline Allen’s rule
- limbs are longer in warmer environments
Serrat, 2012:
* 28 mice in groups of 9
* 7, 21 and 27 °C for 8 weeks
* Measured weekly
* Initial period of rapid temperature-sensitive growth
* Then same growth rates across groups
- tail length changed but only in critical period
- didn’t affect body mass
Outline Allens rule in relation to human population
Pomeroy et al, 2021:
- While human populations tend to follow Allen’s rules a there are other major influences on limb proportions and stature such as resource availability and pathogen load
Outline genetic responses to cold
Key et al, 2018:
- TRPM8: T allele alters response
- codes for a receptor for the sensation of moderate cold temperature
- T allele has been under selection in colder latitudes, e.g., allele frequency is 5% in Nigeria and 88% in Finland
- Evolved neutrally in Africa then high frequency in Europe 3-8 kya
- Selection began c26 kya – around the time of last glacial max
- Associated with migraine
Outline disorders associated with living in cold environments
- Type 2 diabetes
- Inuit population vulnerable
- may have link to diet of cold-adaptive people
- when switch from traditional diet and high activity to normal diet, rates of diabetes increase
- switch from high fat and protein to high carbohydrates from simple sugars and refined grains
- decrease physical energy expenditure
Outline effects of genetic selection on diet in cold temperatures
Fumagalli et al, 2015:
- 191 Greenland Inuit; 20 Europeans; 44 East Asians
- Looked for genetic markers associated with heart disease and metabolic disorders
- Greenland variants: FADS1, FADS2 & FADS3 coding for fatty acid desaturases that determine levels of polyunsaturated fatty acids so that they produce less
- Compensates for fish and seafood diet & reduces ‘bad’ cholesterol and insulin – protects from cardiovascular disease and diabetes – but 2cm shorter in height
Outline genetic markers of diabetes in populations living in cold environments
Graup et al, 2018:
- 1 in 5 Greenlanders are carriers of gene variants associated with a specific kind of diabetes- maturity onset diabetes of the young – MODY
- rare in Western populations- often misdiagnose d
- e.g. ADCY3 variant in Greenland Inuit associated with obesity and diabetes
- leads to reduced gene expression and loss of enzyme function
- those with two copies 15kg heavier, 17cm extra at waist
Thuesen et al, 2022:
- specific HNF1A variant (G-> T) only found in Greenland and accounts for nearly 7% of cases of diabetes- example of mismatch
- 1 in 5 Greenlanders are carriers compared to 1 in 50 in western populations (but different variants)
Outline foetal adaptation to diet
- Mothers pregnant during the Dutch Hunger Winter bore children programmed for famine
- Heijmans et al, 2008- Persistent epigenetic differences associated with prenatal exposure to famine in humans
- Hales et al, 1991- increase in T2 diabetes rates with higher brith rate
- thrifty phenotype hypothesis
Outline the thrifty phenotype hypothesis
Barker& Hales, 2001:
- epidemiological associations between poor fetal and infant growth and the subsequent development of type 2 diabetes and the metabolic syndrome result from the effects of poor nutrition in early life, which produces permanent changes in glucose-insulin metabolism
* mteabollic syndrome- abdominal obesity, high blood pressure, impaired fasting
glucose, high triglyceride levels, low HDL
cholesterol levels
- Metabolic syndrome greatly raises the risk of developing diabetes, heart disease & stroke
- maternal stressors influence in utero programming- alters brith weights causes changes in growth, metabolism and vasculature, over-feeding if now BQ- causes obesity and insulin resistance
Outline modification of gene expression
- Epigenetic changes do not change the DNA sequence – only how it is expressed
- Changes like this are routine for sort- term regulation, but can also be longer term
- methylation- one way to epigenetically regulate gene expression
- e.g. worker vs queen bees based on type of jelly
Outline an example of generic regulation influencing adaptation
- IGF2 gene- codes for IFG2 (insulin growth factor 2)
- hormone involved in regulating growth and cell division
- especially influential on foetal growth
- Expression of the IGF2 gene is strongly influenced by the degree of methylation in the DMR
- Heijmans et al, 2008- Dutch famine- Difference in IGF2 DMR methylation between individuals
prenatally exposed to famine and their same-sex sibling – 60 years later
Outline the link between foetal programming and adult disease
- factors in utero influence foetal gestational programming that predisposes to adult metabolic disease
- e.g. hyperglycaemia, high fat diet, undernutrition, IVF culture may predispose to obesity, insulin resistance, and hypertension
Outline epigenetic across generations
Wei et al, 2014:
- father had pre-diabetes, F1 offspring aha insulin resistance and glucose intolerance, F2 offspring )from offspring sperm) also had impaired glucose tolerance and decreased insulin sensitivity
- Altered gene expression in pancreatic islets incl. genes involved in glucose metabolism and insulin signalling
- Pancreatic islets showed changes in methylation of several insulin signalling genes
- Differentially methylated genes matching those in pancreas
Outline the potential effects of protective foods on the epigenome
- some foods may be able to protect the epigenome
- e.g. Lycopene in Tomatoes effects methylation, anacardic acid in cashew nuts effects histone modification, caffeic acid in coffea effects both
Outline reactions/adaptations to early life stress
- early lief stress linked to Anxiety, Depression, Antisocial behaviour, Conduct disorder, Violent behaviour, Attention deficit disorder
- Early attachment affects stress-sensitivity over the life-time- e.g. if exposure to hostility or low birth weight, environment may overcome genetics in adversity
- Meany, 2005- More attentive rat mothers have less anxious pups. anxious mice make less attentive- question whether genes or environment
Outline epigenetic regulation of early stress responses
- Glucocorticoid receptors (GR) in the hippocampus mop up cortisol and turn off the stress response
- Anxious rats have fewer GR- Meany (2005)
- Glucocorticoid receptor gene- methylated in response to stress- makes less controlled and longer stress response- means more anxious and more vulnerable to depression
- McGowan et al, 2009- Methylation of the glucocorticoid receptor gene promotor in human post mortem brain samples is associated with childhood abuse
- Perroud, 2014- Mothers pregnant during the Rwandan genocide had more methylation of the glucocorticoid receptor gene- also seen in children
Outline paternal epigenetic regulation of stress response
- Rodgers, 2013- stressed male rats lead top offspring with decreased stress response, maybe especially in sons
- may be due to delayed learning/slower brain maturation in sons and being more exploratory
- leads to impaired earning and reduced methylation in the frontal cortex of daughters
- Jawaid, 2020- dietary exposure, psychological stress and toxins transmits effects in humans
- paternal stress impacts behaviours and DNA methylation in the hippocampus of offspring- Enrichment of male rats environment for 28 days before mating has a positive effect on methylation and also maternal care and pup behaviour
Outline the extent to which the stress response is currently adaptive
- short-term benefits and long-term costs
- acute- fight or flight
- Fear is a neural circuit that has been designed to keep the organism alive in dangerous situations- hypervigilance can be useful against real threats to survival- such as increasing numbers of predators
- however, stress today different to stress in Stone Age- Many of our demands are internal and stress results when ruminate about personal goals (Nesse, 2007)- stress from mismatch between what desire and what can have, rather than between abilities and environments demands
- Socioeconomic stress may influence the epigenetic regulation of stress sensitivity and attachment (Miller, 2009)
- e.g. COVID-related prenatal stress influents infants genes- Serotonin transporter gene (SLC6A4) methylation is a potential biomarker of early adverse experiences (Provenzi, 2021)- association between COVID prenatal stress and methylation, and methylation and 3-month urgency score (activity/pleasure expression level)
List potential epigenetic responses to stressors
- Histone modification
- DNA methylation
- miRNAs & lncRNAs
List stressors (epigenetics)
- Foetal/ Prenatal/ Maternal stress
- Early life stress
- Chronic stress
- Poor nutrition
List potential impacts of epigenetic responses to stressors
Changes in:
- Brain plasticity
- Social behaviour
- Reward processing
- Neuroplasticity
- Neurotransmission
- Neuroinflammation
List potential long term consequences of the impacts of epigenetic responses to stressors
- Anxiety & depression
- Anhedonia
- Altered stress response
- Emotional negativity
- Reduced learning & memory
List windows for input into epigenetic influences on development
- Embryonic development after fertilization
- Oocyte development in foetal daughters
- Uterine environment – messages from the mother through the placenta
- Postnatal care
- Puberty – interaction with hormones
- Spermatogenesis prior to fatherhood
When is the prime window for epigenetic programming
Conception to 2 years
Outline the extent to which humans can impact the effect of natural selection on lifespan
- lifespan varies, so could respond too election if all agreed to delay first birth- but people vary reproduction
- Attenborough- stopped natural selection when started being able to rear 90-95% of babies that are born
Outline examples of ongoing selection
- Field et al, 2016- Lactase tolerance and MHC genes are still under selection
- MHC region has been under long-term balancing selection (involved in immune repose)
- evidence for ongoing selection for height, increased infant head circumference, birthweight, increased female hip size
Outline the major transitions associated with changing selection pressures and adaptations
1- Hominins diverge from apes and become upright bipeds
2- Australopithecines broaden diet
3- 2 mya, genus Homo: bigger brained hunter-gatherers
4- Archaic humans spread around the world
5- Modern humans develop language, culture & cooperation
6- The Great Transition: Industrial Revolution, & The Demographic & Epidemiological Transitions: fewer babies, longer lives (current)
Outline the epidemiological transition, including details of variability/evolutionary explanation
3 stages:
1- pestilence and famine
2- reduced infectious disease- where infectious diseases are more prevalent (and health care generally less accessible) – infant mortality and morbidity is strongly impacted
3- increased chronic inflammatory disease- Chronic inflammatory diseases (CIDs) tend to become serious later in life- selection shadow- not selected against, antagonist pleiotropy means may even mean positive selection for CIDs
Outline the demographic transition
- the epidemiological transition drives the demographic transition from high mortality and fertility – to low mortality and fertility
- Timing dependent on different modernisation rates e.g. faster in Germany, slower in Chile (Roser)
- England and Wales- death rates fall faster than births so the population gets much bigger for a while
- 2020- 2/3 world population love in regis where fertility rate below cirtical 2.1 births per woman threshold (allows 1 generation to replace itself- e.g. 0.8 South Korea (but some still high e.g. 6.9 Niger)
- cost of raising child extremely high
outline evolutionary reasons for the demographic transition
- The fitness landscape has changed so that natural selection favours smaller families
- Cultural evolution–spread from person to person by copying behaviour
- A maladaptive response to modern environmental cues
Outline consequences of selection regarding an ageing population
- more old people, fewer younger people
- selection acts even more on reproduction, rather than survival
- Changing selection pressures due to reduced infant and juvenile mortality: expect selection for earlier age at first birth
- Longer lifespan reveals chronic disease due to antagonistic pleiotropy
Outline section for age at first reproduction
- Age at first reproduction is more heritable now than in preindustrial society
- varies more due to use of contraception
- is now choice- may increase influence of genetic disposition
- culture and biology may influence who is having how many babies and why
- analyse by looking at fertility and mate choice
Outline the potential for evolving out of the demographic transition
Burger et al, 2016:
- Selection for high fertility variants
- Changing cultural norms
- Modernisation may become too costly, e.g., per capita energy use
- Increasing wealth inequality could e.g., limit spread of low-fertility norms
- Reduced costs (money, time and career progression) of childrearing
Outline measurement of fertility to look for signs of current selection
Stulp et al, 2016:
* Measures include reproductive fitness e.g. as a composite of lifetime no of children and age of having children, age at first birth and other traits
* Often makes use of available secondary data e.g., birth and death registers
* To be under selection the trait must be genetically heritable
Outline issues of measuring fertility to look for signs of recent/current selection
- Actual changes in allele frequencies not established
- Lifetime reproductive success may not reflect longer term fitness, i.e. cost to future generations
- Population growth interacts with fitness, e.g. a well-timed birth in a growing population may have a greater influence on fitness than the production of additional numbers of children
Outline a study showing selection for earlier age at first birth
Kirk et al, 2001:
Australia, Female twins age > 45 Broad heritability:
* menarche 50%
* age at first reproduction 23%
* menopause 45%
- Age at first reproduction and to much smaller extent, menopause, correlated with overall reproductive fitness\
- Suggests that age at first reproduction and possibly menopause are under selection
- Education and religion only 2% & 1% of fitness variance
Outline a study regarding current human evolution processes
Byars et al, 2010:
- using the Framingham Heart Study
- longitudinal, multigenerational study
- traits measured- total cholesterol, systolic blood pressure, diastolic blood pressure, blood glucose
- results- evidence of slow evolutionary change
- over 10 generations women would be 1.3% shorter, 1.4% heavier, have reduced cholesterol by 3.6%, and have reduced blood pressure by 1.9%, have first child slightly earlier, and reach menopause slightly later
- selection intensity, but not direction, varied over time
Outline research of the demographic transition recently happening
- Gambia- transition occurred in 1970s
- selection changed- pre transition- selection acted to decrease height and increase BMI
- post-transition- to increase height and decrease BMI
- variance in fitness decreased, but selection didn’t decrease
Outline the relationship between menopause timing and reproduction
- increasing time length between menarche (first period) and menopause gives a longer opportunity for reproduction
- however culture favours later age at first birth
Outline possible effects of social factors on fertility selection
Mathews, 2013:
- 594 women, age 17-44, from the British Household Panel Study 1992-2003
- Odds of having a second child were increased by:
* Having relatives to provide childcare
* Contact with emotionally close relatives
Independent of socio-economic variables
Outline how current selection can be analysed using genetics
- GWAS for signals of selection
- Correlate polygenic trait scores (PGS) with fitness
- PGS are the summed allele counts (effect sizes) of SNPs associated with a trait in a GWAS
- Population PGS generally have a normal distribution – so meaningful risks predictions are at the extremes
Outline an example of polygenic risk scores suggesting current selection
Mullins, 2017:
- Icelandic population- N>150,000
- higher polygenic risk scores for autism was associated with having fewer children
- ADHD was associated with having more children
Outline the link between genetics and variation in current reproductive fitness
Mathieson et al, 2023:
- GWAS- N>785,000 Europeans
- 43 loci associated with number of children ever born (NEB) or childlessness
- Loci relate to puberty timing age at first birth, sex hormone regulation, endometriosis, age at menopause
- Most significant NEB-associated variant CADM2 shows signal of balancing selection-associated with risk-taking
- Second most significant, ESR1 (oestrogen receptor 1) also shows balancing selection
Outline examples of genes associated with being under strong selection in the past
- new role for the MC1R gene for the melanocortin 1 receptor required for the synthesis of skin and hair pigment
- Strong signal of FADS1 & FADS2 selection known to have been under selection multiple times in the past: the variant increasing FADS1 expression increased form <10% 10 kya to 60-75% in present-day Europeans- code for enzymes involved in lipid metabolism
Outline evidence regarding the link between genetic selection and education
Beuchamp, 2016:
- 20,000 N from US
- Polygenic scores for individual genotypes predicting education attainment, age of menarche (also BMI/height/cholesterol etc)
- tested scores against fitness
- results suggest natural selection favoured lower educational attainment in both sexes, and higher age of menarche
- but rate of selection for education very slow
Note- The environment, especially culture, can override genetics, e.g. there has been an increase of c 2 years education/generation in the US; population source biased- higher SES live longer so able to take party in study
Outline issues with using genetic studies for current selection
- Time spans are short: selection needs to act consistently over many generations to produce genetic changes
- The genetic architecture underpinning the ‘traits’ is poorly understood, e.g. how causal are the genetic components of a polygenic score for educational attainment?
- Phenotypic traits are hard to define and measure precisely, e.g. years of education as a proxy for intelligence
Outline the influence of mate choice on selection/genetic diversity
- Can shape genetic diversity via assortative and dissassortive mating
- Drives sexual selection
- Influences reproductive success
- Cultural evolution impacts mate choice- e.g. online dating- Ponseti et al (2022)- review of 13 studies showed makes men more active in making contact, makes women more likely to a accomplish sexual goals due to male demand, but presences broadly in line with real world studies e.g. education more preferred in males
- males more likely to give dishonest signals of fitness, M more likely to lie about height, females about weight
- impact of social media on assortive mating- Partners tend to choose from similar educational, religious and ethnic groups: couple endogamy- less endogamy found in German sample in race/education/religion (Potarca, 2017)
List factors that may drive selection in the future
- Climate change
- New infectious diseases
- Antibiotic resistance
- Genetic engineering
- Changing cultural norms
Space travel and living on another planet
Summary of current adaptation/evolution
- still evolving – but it is effectively impossible to select for immortality
- Many adaptive human traits, such as lactase tolerance and malaria resistance are still under selection
- The epidemiological and demographic transitions reduce mortality and fertility and impact selection so that it acts mainly on fertility behaviour
- Selection still acts on biological fertility – but cultural influences are probably stronger with the overall result of decreased fertility in transitioning populations
- Heritable influences on reproductive choices may be under selection
- Cultural evolution greatly impacts reproductive fitness via reproductive choices including mate choice
Outline selection pressures at high altitude
- very physiologically challenging
- oxygen partial pressures drop
- At 4500m (the approximate limit of human permanent habitation) oxygen pressure is 40% lower than at sea level
- 5% world population (140 million) live > 2500 m
Outline the impact of altitude on oxygen levels
- As the partial pressure of oxygen drops, you have to breath deeper and faster – but at some point, won’t be able to make up the difference resulting in hypoxia
- means less oxygen in the system- means physical performance worse at higher altitudes
- Partial pressure of inspired O2 (PIO2) is decreased in mountainous regions
Outline the immediate adaptive response to acute hypoxia
- Hyperventilation: rate & depth
- Haemoconcentration via reduced plasma volume
- Increased heart rate & cardiac output
- Pulmonary vasoconstriction
- Elevated arterial pressure
Outline acclimatisation to altitude
- Depth of respiration increases
- Pulmonary artery pressure increases to increase lung-blood oxygen exchange
- More red blood cells
- Increased release of oxygen
from haemoglobin - brain protection- angiogenesis, cerebral blood flow regulation, neuromuscular coupling and blood-brain barrier
- takes 3-7 weeks depending on altitude- 1800-4200m
Outline types of maladaptation to high altitudes
- acute mountain sickness- commonly induced by mild-moderate hypoxia
- Subacute mountain sickness- HAPE- deadly- Affects c10% of people living long-term 2500-5500m
- Chronic mountain sickness: Monge’s disease- especially common in Andean populations
Outline acute mountain sickness
- Typically occurs >2500 m
- Affects 10-25% non-acclimated ascending to c2500 m & 50-85% at 4500-5500 m
- Incidence rises 13% for each 1000 m > 2500 m
- Starts 6-12 h and worsens with altitude- but self-limiting over 4 days at the same altitude
- symptoms- headache, weakness, loss of appetite, nausea, vomiting, dizziness, facial/peripheral oedema (swelling)
- vest treatment is to decline
Outline subacute mountain sickness (HAPE)
- Most common cause of high-altitude related death
- Increasing pulmonary capillary pressure and cardiac output are triggers
- Can occur 2-5 days above 3-4000 m- depends on altitude, rate of ascent, and individual susceptibility
- Decreasing consciousness signals onset of cerebral oedema leading to coma and death
- Can be chronic after several months at high altitude due to pulmonary vasoconstriction leading to persistent pulmonary hypertension and right ventricular enlargement in the heart; differing susceptibility across populations
Outline chronic mountain sickness
- Up to 20% Andeans affected
- Extreme polycythaemia & erythrocytosis
- Hypoxaemia
- Pulmonary hypertension but…
- Peripheral arterial pressure dops
- Right side of heart enlarges
- Can lead to congestive heart failure
- Only treatment is to go to lower altitude
List locations where populations have exhibited adaptation to high altitudes
Bigham (2008):
- Andean Altiplano, the Semien Plateau (Ethiopia), and the Tibetan Plateau
- populations show very different physiological responses to high altitude
Different physiological response to high altitude across populations table- red blood cell concentration, haemoglobin concentration, partial oxygen, stature, lung volume
Outline variation in blood flow to the brain across high altitude population
- Claydon et al (2008)- blood flow maintained more stably in Ethiopian compared to Andean
- Ethiopian- vasodilation in response to changing Co2 is greater may explain why cerebral blood flow is not restricted at high altitude compared to Andeans – and why CMS is in the Ethiopian highland population
Outline scales of adaptive challenges of high altitude
- those affecting old age not acted upon by natural selection- Julien et al, 2019
Outline reproductive fitness at high altitudes
- Tibetan women have lower prenatal and postnatal mortality than Han Chinese women (usual lowlanders) living at 3000-4000m
- may be because don’t over produce haemoglobin
Outline the relationship between birth weight/uterine blood flow and high altitude living
- Niermeyer et al, 2009- tends to drop 100g for every 1000m of altitude
- drops most in Han, elast in tibetan
- Julian et al, 2008- maternal blood supply strong influence- vasoconstriction at high altitude reduces uterine blood supply - level of endothelia relative to nitric oxide metabolites in the maternal circulation elevated in non-pregnant state
- at higher altitude, women with higher uterine artery blood flow had heavier babies
- Moore et al, 2001- Pregnant Tibetan women have higher uterine artery blood flow velocity to counter falling arterial oxygen content- newcomers who become pregnant don’t show this response
Outline genetic signatures of birth weight adaptations at high altitudes
Bigham et al, 2014:
- PRKAA1 & EDNRA SNP polymorphisms are associated with birth weight at low or high altitude
- PRKAA1 is associated with uterine artery diameter and metabolic homeostasis: EDNRA is involved in oxygen sensing
Outline developmental differences associated with high altitude adaptation
Llapur et al, 2013:
- Delayed body growth but accelerated lung growth – especially in males
- Increased erythropoietin (both sexes)
- adaptation not thirty phenotype as not sacrificing hand/foot in Peru (Pomeroy et al, 2012)- these are priority- Nepal also (Payne et al, 2018)
Outline genetic regulation of the physiological response to hypoxia
The form and function of hypoxia inducible factors (HIFs) respond to changes in oxygen availability- regulated by several genes:
* HIF1A: transcription factor
* EGLN1: oxygen sensor influencing HIF1A expression
* EPAS1: transcription factor, reduces red blood cell count so protecting from overly think ‘sticky’ blood.
* EPO: erythropoietin, increases red cell production
* PPARA: increases red cell count
e.g. Sherpa - more efficient mitochondria and muscle, maintain blood flow- partly due too PPARA gene variant
Outline convergent adaptation in high altitudes
Azad et al, 2017:
- Convergent adaptation of the erythropoietic response and cardiovascular system in Tibetan, Andean and Ethiopian populations living at high altitudes
Outline adaptation to high altitudes in germs of haplotype and admixture
- Huerta-Sánchez et al, 2014- Haplotype pattern in a region defined by SNPs that are at high frequency in Tibet and at low frequency in the Han- Includes EPAS1 which shows a very strong signature of selection in Tibetans- illustrate that admixture with other hominin species has provided genetic variation that helped humans to adapt to new environments
- Jeong et al, 2014- Tibetan adaptation to high altitude also reflects admixture between ancestral H. Sapiens populations- Tibetans show a depletion of Han ancestry and enrichment of Sherpa ancestry around EPAS1 and EGLN1
Outline an integrated approach to amass of high altitude adaptation
Yu et al (2022)- should combine epigenetics, genomics, transcriptomics, proteomics and metabolomics
Outline an example of an epigenetic response to high altitude that isn’t necessarily adaptive
- Alam et al, 2020- upregulation of specific miRNAs can lead to a cascade of altered gene expression resulting in HAPE (high altitude pulmonary oedema)
Compare adaptation to high altitude at the individual and population level
- individual- environment influence on genotype, phenotype and fitness
- other evolutionary forces (demography, mutation, recombination) and allele frequency trajectories alter generic variation patterns
Cultural adaptation to high altitude- food
- Tang et al, 2023- lots of grazing land
- Dairy pastoralism- enabled widespread settlement of Tibet at least 3500 years ago- Evidence from dental calculus of 40 individuals 1500-1312 BCE, northern Tibet- no evidence for milk drinking in lower arable farming areas
- Li et al, 2023- Subsistence Tibetan agriculture is dominated by family farms. Four subpopulations were identified and 2 common gene variants and many non-overlapping variants
- Andes- Chuño- nutritional potato-based food source which can be preserved for decades- Yoshikawa et al, 2020; quinoa, guinea pig meat
- Ethiopia- domesticated teff (small seeds which grow best at 1700-2200 metres- Belay et al, 2023; Rodents key food source (Ossendorf et al, 2019)
Cultural adaptation to high altitude- housing/social
Moore et al, 1988:
* Insulated housing style (unless temporary), e.g. adobe houses in the Andes
* Tight woven, layered clothing and baby-carriers.
* Co-sleeping for mothers, infants, and families
* Lowland women who move to higher altitudes move back to lowland family while pregnant and stay with or leave infant until child is 1-2 years
* Protecting child nutrition; scheduling of low-energy activities with low-food periods e.g., Andes temporary outmigration of males to protect food provisions for children.
* Use of child labour that is ‘cheaper’ to fuel, e.g., a 12-year- old child can herd like an adult for 30% fewer calories.
* Animal dung for fuel in place of wood
* Strong traditions of local trade and exchang
