Human Ecology II Flashcards
(55 cards)
Recap: Human adaptations to a density independent (abiotic) regulating factor: Ultraviolet
radiation
Humans evolved in tropics
UV high in tropics
UV interferes with folate synthesis; produces skin cancers
Adaptation 1st to tropical levels of UV (high) via melanin
UV lower penetrance with darker coloured skin
Phenotypes with more melanin in skin => protect folate synthesis
=> minimize damage
=> selective advantage where UV high
but not where UV is lower
Dispersal to non-equatorial environments
Humanitudes dark skins migrate from equatorial to higher less UV (less light) colder so more of body covered (evidence for
“clothing” approx. 150 KYA) before “out of Africa”
Increases phenotype of lighter skin to
increase UV-B to respond to Vit D limiting/regulating factor
Migrant populations from high latitudes to lower latitudes show skin darkening… (reversal of the phenotype due to same adaptive process in reversed selective environment)
Adaptation & Acclimatization to UV
One additional comment about responses to the environment.
UV important selection pressure:
1) genetic adaptation (melanin/ skin color)
2) acclimatization (tanning)
Both a genetic response and a plastic response (ability to mobilize melanin based on individual’s recent exposure)
Predictions from these hypothesized selection pressures on tolerances:
Clinal (incremental changes that correlate with environmental measure of UV and temperature;
latitude)
Yes
High altitude (cold) populations will have shorter thicker stature than nearby lowland populations
Yes
More recent migrations will show more exceptions to skin color and latitude clines than areas occupied longer by humans
Yes
Roadmap
Why racial groupings isn’t a biologically defensible
categorisation.
Variation within and among populations
Geographic clines (e.g blood group frequencies)
Malaria
Lactose tolerance
Skin colour and race classifications
Skin colour has biological basis
Race classifications have no biological
basis
HEIGHT MEASUREMENTS OF MALES
Arbitrary
A social construct traditionally based on external morphology
Skin colour occurs in a cline
complex genetic trait (polygenic)
(i.e height as example of cline)
eumelanin (brown black) and pheomelanin (reddish yellow)
no discrete shifts in phenotype
Variation within groups vs. among groups
88% of genetic variation is among individuals (within populations); only 9.2% among continents.
Polymorphism = variation within a population (much)
Polytypism = variation between populations (very little)
Patterns in external features are not representative of the entire genome
Reflect population-specific adaptation or founder effects
Racism emphasises variation between groups when most of the
variation is within a group
Racism is a social phenomenon without a biological basis (but it can have a social and biological outcome. E.g health differentials)
Why did the idea of “races” (race-based groups)
arise?
Sampling problem (small samples at large distances)
Biotic selection pressures
Abiotic: non-biological, non-living
light, temperature, humidity; earthquakes,
floods
Biotic: biological, living
pathogens (Zika virus,Covid-19) predators, prey (food)
You survived a period of
heightened biotic related mortality (Covid-19);
We don’t know extent to which this is a selection pressure.
Maybe lower selective pressure than Zika? Why?
Malaria
Plasmodium parasite (numerous types)
Vector is Anopheles mosquito
“Strongest ongoing selective pressure”
Every 2 minutes a child dies of malaria
(WHO 2018) Africa increase, SE Asia decline
Many apparent genetic responses
Sickle cell
Thalassemia
When a similar phenotypic change results from varying genome changes in different population
= convergent evolution
Sickle cell allele is advantageous against
malaria
Sickle cell: phenotype is ‘sickled’ red
blood cells less susceptibility to
malaria (benefit) but less oxygen binding capacity (cost)
(this is an example of a trade-off)
Malaria: Cultural changa
Slide 2hvironmental change =>
change in selection pressure and genetic evolution
Distributions of sickle cell red blood cells and malaria are similar
Selective pressure & adaptive response
Fitness of sickle cell genotypes in different environments (survival rates)
Sickle cell not the only anti-malarial adaptation?
Thalassemia:
More complex, 4 genes involved;
also affects
structure of
hemoglobin
A-thalassemia
■ Malara
■ Thalassaemla
Malaria and thalassaemia
some
Malarial
protection
Convergent evolution: two different genetic responses in different populations that produce similar phenotype in response to similar environmental selection pressures.
Cultural responses to malarial environment
Smoky interiors of living quarters
Behavioural avoidance of mosquito breeding areas
Clothing (sleeves and legs) & bed nets
Elimination of mosquito habitat
Chemical actions to decrease mosquito populations (insecticides)
Chemical actions to repel mosquitos (mosquito
repellents e.g DEET)
e.g. Timor-Leste last 10 years: Malaria 220/1000 to 1/1000 (standing water decrease, bed nets, anti-malarial drugs, spraying)
Evolution of Lactose tolerance
(= Lactase continuation)
Lactose intolerance is ancestral condition.
Symptoms when ingest milk after weaning:
- Abdominal swelling and pain
- Flatulence
- Diarrhoea
10 KYA to 7 KYA: Some human populations began herding, archeological evidence of fermentation to break down lactose (behavioral cultural adaptation)
6.5 KYA : LCT mutation => lactose tolerance
LCTR (recessive wild, stops lactase) LCTP (dominant, lactase continues)
Revise Dr Gaudieri’s discussion of genetics of this phenotype
Cultural adaptation to eating dairy
(7-10 KYA)
Fermentation
Lactobacillus bacterium digests lactose to lactic acid
Energy benefits of dairy without cost of intolerance symptoms kefir, yoghurt, cheese
