Human adaptation Flashcards
do humans have lots of genetic variation?
no, despite a high phenotypic diversity, there is little genetic diversity (99.9% identical)
Are we one species?
we are one species under the biological species act - based on reproductive isolation
Cite Mayr - biological species concept
why study genetic variation
can tell us about the evolutionary history of our species, along with archeological evidence.
genetic evidence
- we can estimate age of our species based on genetic diversity and mutation rates
e.g. mitochondrial DNA inherited maternally - Mitochondrial eve (most recent common female ancestor) like 100-200kya
founder effects
repeated migrations cause population bottlenecks, reducing genetic diversity
complex family tree
modern humans, Denisovans, neanderthals
neanderthals
- genetic evidence has revolutionised our relationship to neanderthals
- extinct human lineage co-existing with sapiens in Eurasia from -45-40 kya
- ancient DNA extracted from Neanderthal bones shows evidence of interbreeding
- up to 4% of your DNA from neanderthal (highest in non africans)
Denisovans
- extinct and mysterious human lineage also living alongside sapiens in Asia
- very few physical remains : existence largely inferred from bones/teeth
- up to 6% of your DNA comes from Denisovans (highest in Melanesians)
- some of the denisovan genomes comes from an unknown ‘ghost lineage’
Are we still adapting?
Yes -
example: malaria Cape Verde
- Cape Verde island settle by Portuguese colonisers and west African slaves - 1460
- west africans lest vulnerable to malaria due to DARC gene allele
- Rapid selection in 500 years where malaria prevalence highest
other examples of adaptations in last 1000s of years
H2 inversion, Lactase persistence, sickle cell alleles
(read sources)
how do we know humans are still adapting - genetics
- inferred from genetic variation
- positive selection results in increase in frequency and reduction in diversity
- also detectable by linkage disequilibrium (hitching neutral genes)
adaptations vs adjustments
adjustments - non-genetic responses to environments within organisms lifetime AKA phenotypic plasticity
adaptations - genetic responses to natural selection - permanent and heritable
Adjustments
Behaviour - learned, often culturally transmitted
Acclimatisation - temporary, referable physiological response to environment
Development - changes to physiology during growth, often permanent
skin colour as an adaptation to climate and altitude
- skin colour highly variable across human individuals and populations, and highly heritable
- polygenic trait - many genes for continuous variation e.g. MCR1 and MFSD12 affect melanin pigment
- has a clear latitudinal gradient, for variation in UV
- Lowe latitudes - high UV - increased risk of skin cancer etc
BUT latitude not only driver - Inuit people
body size and proportions
highly variable, also heritale
Bergamanns rule - body size larger at higher latitudes (colder religions)
Allens rule - body shape generally stockier at high latitudes (colder)
SA: V ratio
BUT - lots of ‘scatter’ not very strong correlation. other explanations? e.g. samoan thrifty genes
risk of high altitude environments
if unclimatised, feel altitude sickness 2500m above sea level
can lead to hypoxia and life threatening conditions
Adjustment for high altitudes:
behaviour: limiting physical activity, ascending gradually
acclimatisation: faster heart and respiration rate, higher haemoglobin production
development: slower growth rates
adaptations for high altitude
High altitude Tibetans and Ethiopians have mutations of EPAS1 gene
- for most people, EPAS1 increases haemoglobin production at high altitude
- but the mutation inhibits HG production
- prevent negative effects of long term HG elevation (e.g. clotting)
is ‘race’ a biologically meaningful way of classifying human variation
No - AABA statement:
“race does not provide an accurate representation of human biological variation”
what is race?
- discrete social categories based on perceived ancestry and characters
- different from ethnicity but confused often
- humans vary by ancestry but this does not map to race
- historically in biology race meant distinct populations within a single species
Biological reality of human genetic variation
clinal not discrete, young practically homogenous species, more genetic variation within than between population, race not equivalent to ancestry
