Human Ecology II

Question 1

Recap: Human adaptations to a density independent (abiotic) regulating factor: Ultraviolet
radiation

Answer 1

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

Question 2

Dispersal to non-equatorial environments

Answer 2

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)

Answer 3

Question 4

Adaptation & Acclimatization to UV

Answer 4

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)

Question 5

Predictions from these hypothesized selection pressures on tolerances:

Answer 5

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

Question 5

Roadmap

Answer 5

Why racial groupings isn’t a biologically defensible
categorisation.

Variation within and among populations

Geographic clines (e.g blood group frequencies)

Malaria
Lactose tolerance

Question 6

Skin colour and race classifications

Answer 6

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

Answer 7

Question 8

Variation within groups vs. among groups

Answer 8

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)

Question 9

Why did the idea of “races” (race-based groups)
arise?
Sampling problem (small samples at large distances)

Answer 9

Question 10

Biotic selection pressures

Answer 10

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?

Question 11

Malaria

Answer 11

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

Question 12

Sickle cell allele is advantageous against
malaria

Answer 12

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)

Question 13

Malaria: Cultural changa
Slide 2hvironmental change =>
change in selection pressure and genetic evolution

Answer 13

Answer 14

Distributions of sickle cell red blood cells and malaria are similar
Selective pressure & adaptive response

Answer 15

Question 16

Fitness of sickle cell genotypes in different environments (survival rates)

Answer 16

Question 17

Sickle cell not the only anti-malarial adaptation?

Answer 17

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.

Question 18

Cultural responses to malarial environment

Answer 18

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)

Answer 19

Answer 20

Question 21

Evolution of Lactose tolerance

Answer 21

(= 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

Question 22

Cultural adaptation to eating dairy
(7-10 KYA)

Answer 22

Fermentation

Lactobacillus bacterium digests lactose to lactic acid

Energy benefits of dairy without cost of intolerance symptoms kefir, yoghurt, cheese

Answer 23

Answer 24

Question 25

Summary

Answer 25

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)

Answer 26

Answer 27

Question 27

Recoup

Answer 27

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

Answer 28

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.

Answer 29

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

Question 30

Roadmap

Answer 30

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

Question 31

Evolution of Homo sapiens

Answer 31

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

Question 32

Foragers

Answer 32

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

Question 33

15-20 KYA Settlement

Answer 33

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

Answer 33

Question 34

Human evolution & dietary trends

Answer 34

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 +

Answer 35

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

Question 36

Human cultivation and selective propagation

Answer 36

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)

Question 37

Population processes (Demography)

Answer 37

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

Answer 37

Answer 38

Answer 39

Answer 40

Answer 41

Answer 42

Answer 43

Answer 44

Question 45

“Behavioural Solutions” in the past

Answer 45

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

Question 46

Intrigued by this area of human biology???

Answer 46

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)

Question 47

Conclusions

Answer 47

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.

Answer 48

Answer 48

Question 49

Signals of positive selection (genetic evidence that evolution of humans continues)…

Answer 49

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)