Human Ecology II Flashcards
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
Summary
Three examples of more recent human responses to environment that occur after humans migrate out of Africa to very different environments.
Biological (adaptation & acclimatization)
Cultural (behavioral responses)
Recoup
Humans subject to laws of physics, abiotic and biotic selection pressures
Mammals therefore sensitive to temperature and to factors like UV
Most of human evolution occurred in
Africa in the tropics and subtropics
Homo sapiens have evolved over several hundred thousand years
during a period of varying global climate
Populations left Africa and colonized different places with different environments/conditions from at least 70 KYA onward
Adaptation is complex; tit does not happen without the origin of a
RANDOM mutation that changes the phenotype in a way responsive to a regulating or limiting factor in the particular environment in which it occurs.
Humans can respond to selective pressures through acclimation and
aclimatization, this is called plasticity
Examples of human adaptation within the last 10KY include sickle cell
(~7500 YA) and Thalassemia as responses to malaria and post-weaning lactose tolerance (~6500 YA)
Evolution of social learning and communication => cultural adaptation
Roadmap
Human Ecology in the last ~ 10-15 thousand years environmental changes (warmer, less variable) settlement of HG food production (horticulture & agriculture) humans change environment to increase food (carrying capacity)
Humans continue to evolve
Humans also specialize in altering their environment
Humans “outsource” work energy to abiotic sources
Contemporary ecology
Evolution of Homo sapiens
Earliest humans 200 KYA to 15 KYA:
large brains for body size, omnivores (eat at all trophic levels) migrant in small bands of relatives complex tool kit & problem solving controlled use of fire
Foragers
Foragers for 180,000+ years
extract food from environment
“high quality” foods
fruits, tubers, sometimes meat, honey,
Small related bands 20-50 people
Mobile: reduced foraging success => move accumulate only what can carry
15-20 KYA Settlement
Horticulture (tropical)
less migrant settle for months to years encourage edible plants over inedible higher population density
more organized intergroup conflict
~15KYA -12 KYA: Agriculture origins on 3 continents
food production (grains) less diverse diet animal production and labor increased human fertility and mortality rates
Human evolution & dietary trends
Cooking: changes the
cost of digestion available nutrients
Homo
neat eating
cooked food (co
availability of a food
Australopithecu:
ouch. hard food‹
More important to eating fibrous starchy foods than meat
alized. mixed diet
Did cooking allowed evolution of large human brain?
strong evidence suggestive evidence/
. Orrorin
Sahelanthropus
F. Luca, G.H. Perry, and A. Di Rienzo 2010 doi: 10.1146/annurev-nutr-080508-141048
(R. Wrangham 2009 “Catching Fire:
How cooking made us human”)
Agriculture (w/ cooking) =>
Diet of largely cereals and simple carbohydrates
Increases fertility ++
10
Increases mortality +
Changes in foods grown by humans (or why you can’t really eat Paleo)
Larger, reduced protection, increased flesh relative to stone, sweeter
Caloric yield per unit of work to gather now much gre ater
Human cultivation and selective propagation
Early humans forage plants and thus act as
“selection pressure” on the plants
Facilitate plants that yield more human food
Select for higher yield (bigger, faster
development)
larger grains, sweeter larger fruits fewer plant protections (toxins, spines)
Evolution through “artificial” selection
Increases carrying capacity (increase availability of a limiting factor)
Population processes (Demography)
Populations change in number and composition
N = population size
Numbers change through births (b) and deaths (d)
and immigration and emigration
r = natural rate of increase
Global population so: won’t talk about immigration & emigration
“Behavioural Solutions” in the past
Migrate to virgin areas (where resources not depleted)
Cultivate food plants and animals (apropriate more of total
primary productivity)
already very high
Expand area under cultivation (pretty much done this already)
Augment productivity / plant or animal artificial selection
Substitute sources of energy for cultivation (petrochems limiting)
Subsidize local nutrients (fertilizer)
Reduce competitors (insecticide, herbicide, etc)
Modify plant to increase productivity (genetics)
These are pretty much guided variations but each step gets a bit harder; less efficient at base level
Intrigued by this area of human biology???
Biological Anthropology stream:
Human Variation ANHB2215
Human Evolutionary Ecology
ANHB3315
Genes &Society ANHB3321
Human/Primate Social Organization ANHB3322
Not an ANHB major?
Minor in Biological Antropology (as above)
Conclusions
Homo sapiens evolved in a tropical environment
Species wide adaptations physiological & behavioural
Later spread throughout the world
population specific evolution (founder effects and natural selection)
Major change in human evolution was settlement and then
development of agriculture
Natural selection has no foresight (what was adaptive 20
KYA may be detrimental today)
Cultural adaptation depends upon prior genetic adaptation (e.g. brain, social transmission of information, etc) “preadapted” )
Both genetic and cultural evolution are ongoing.
Signals of positive selection (genetic evidence that evolution of humans continues)…
Digestive enzymes Increases: copies AMY1 gene (amylase production) ‘
Europe &Asia higher than HG origin popns
Skin pigmentation (OCA2, MYO5A,
DTNBP1, TYRP 1 in Europeans)?
Carbohydrate metabolism: 2
Alcohol dehydrogenase (ADH East Asian), Mannose (MAN2A1 Yoruba)
Sucrose (SI East Asian) Lactose (LCT European)
Microbiome components (bacteria of the human gut) ‘
(Japanese microbiota w gene to degrade porphyrin found in popns with seaweed diet)
Development of microbiome affected by Caesarian sections, formula, small households and refined CHO diets ‘ (MORE IN 2nd YEAR)
