Week 11 Flashcards
Where you place humans on the tree of life?
Primate phylogeny -> numerous derived characteristics
Clearly most related to great apes (hominidae)
When did the branch leading to humans split off of tree of life?
Consensus from many independent gene sequences
Human most related to chimps
Molecular clock - separation 5.4 mya
What are the Homini?
Humans, extinct ancestors and related races/species
How many taxonomic groups within great apes?
Within the great apes (Hominidae) – four taxonomic groups (tribes)
Orangutans, gorillas, chimpanzees and humans.
What is an overview of the oldest hominins?
Oldest – Sahelanthropus tchadensis
Discovered in Chad, central Africa – ca 5-6 Mya
What are examples of other hominin forms?
Homo Habilis
Homo erectus
Homo heidelbergensis
What is an overview of the hominini despersal?
Homo genus range expansion out of Africa approx 1.8 MYA
Homo erectus like forms (archaics) spread across the world
Resolving between these species remains controversial
What was an overview of the different forms between the different forms around the world?
Recent evidence suggest that different forms were members of a single species
H. erectus - a very successful species – surviving 1.8 million years
Modern humans – only very recent
What makes us human?
Use of complex tool industry is the definition of humans (homo)
Increased cognitive abilities - brain size
H. erectus developed tool and cultural technologies
Advances may have lead to expansion of Homo species across the globe 1.8 Mya
What are potential key drivers for human cognitive abilities?
Feedback loops caused by tool use and/or social interactions between species
What is the evolution of bipedalism?
Footprints - Australopithecus afarensis - 3.3 Mya
Seen in upright bipedal, free striding gait – well developed arch to the foot
Why did bipedalism evolve?
Frees the hands for fine manipulations
Greater stamina for long distance travel
More effective hunting
Improved ability to carry food
What is the evolution between bipedalism and human habitats?
Many theories link bipedalism to living in a savanna – where A. afarensis lived but prior to this A. anamensis (4mya) – thought to be bipedal - existed in dry woodland
What are the differences between humans and other great apes?
Gorillas, Chimps, n = 24 chromosome pairs
After split from chimps, 2 chromosomes fused (12 and 13)
Humans n = 23
What is the genetic differences between humans and other great apes?
1% if focus on coding sequences in genome
5% all regions (incl insertions and deletions)
Which genes make us human?
80 genes in chimps – disabled in humans
Functional differences in genes related to sensory perception, immune defence, spermatogenesis
In key organs what are the differences between human and chimp compared to rhesus monkey?
Blood human and chimp equidistant to rhesus
Liver human slightly more diverged than chimp
Brain human massively diverged compared to chimp
Where did humans evolve?
Generally agreed – evolved in east Africa
But Henn et al 2011 PNAS. >500,000 markers – indicates S. African origin?
What are the two origins of modern humans?
Out of Africa
Multi-regional evolution
What is an overview of out of Africa theory?
Emerged recently in Africa – spread and replaced archaics
What is an overview of multi-regional evolution theory?
Hominin populations - evolved in situ into modern
homo populations – with gene flow between
Implies ancestral forms = not biological spp
Which theory for the human evolution was correct?
Fossil evidence could not refute multi-regional evolution hypothesis
Genetic/genomic evidence indicates there was recent expansion & replacement by H. sapiens
Out of Africa theory
Did non-African archaics contribute to the gene pool of modern humans that expanded into each region?
2% Neanderthal DNA in non-African Humans
4-6% Denisovan DNA in Melanesian humans
What is an overview of the Origin of Humans?
Humans – demographically young species
From east or south Africa – ca. 100,000 years ago
Recent expansion - with small sequential colonisation events
What is the relationship between H.sapiens and other hominins?
Replaced archaic forms of hominins – with some inter breeding
H. Sapiens – lone survivors of extinct radiation of bipedal African hominins
What is the effective population size of humans?
Approx 10,000
What is the genetic variation between humans?
6 % sequence divergence
All humans – closely related!
How has genetic variation of humans measured?
mtDNA – pairwise comparison between random individuals within each species
What is the genetic variance of other great Apes?
Gorrillas - 22%
Bonobos - 11%
Western chimpazee - 16%
What is the FST for humans?
Genetic variation – Fst between populations
Worldwide Fst = 0.15;
so 80% of variation found within populations and only 20% among populations
What is an overview of the genetic variance between humans?
Human genetic variation cannot be subdivided into sharply defined discrete races
Most of what variation there is was left in Africa
What can determine genetic differences between populations?
Subtle differences exist in alleles frequencies at specific loci between populations.
Accumulated - determine statistical genetic differences between populations
What are examples of the eight classes of genetic similarity?
Western and Southern Europe + Africa
Northern Europe + Eastern Europe + Iran
Australia
What are fine scale examples of genetic structure in the UK?
Distinct unique genetic groups in Cornwall, Devon, Northern Wales, 2 in southern wales
What is gene flow like since human expansion?
Global Fst – 0.15 - low levels of gene flow since human expansion
Ca. one individual per generation between continents
No obstacle to changes being caused by selection
How did they prove that humans are still under selection?
Expected distribution of Fst of loci across the genome because of drift (without selection) vs observed distribution
More loci with higher Fst’s than expected = identifies genes under selection
What is an example of human evolution of a key trait?
Lactose tolerance
What is an overview of the relationship humans have with lactose ?
Lactose – nutritional carbohydrate in milk
Broken into glucose/galactose by Lactase
Only active up to weaning age in other mammals
Most humans (70%) cannot digest Lactose – intolerant to large amounts of unfermented milk
What is the histroy of the evolution of lactose tolerance?
Persistence of lactase into older age – Northern European populations
Polymorphism upstream of the LCT gene – associated with lactase persistence
Frequency of the polymorphism – matches geographical distribution of dairy production
What caused the ability to tolerate lactose?
Lactase persistence allele – In European humans, = recently single mutation
Found in haplotypes (sections of linked genes) that are homogenous over long sections of genome – recombination hasn’t had time to break up ancestral sequence
When was the rough origin of the mutation for lactose tolerance?
Length of haplotype – consistent with origin of this variant 10,000 years ago
Roughly when dairy cattle farming became established in Europe
What is the overview of human skin colours?
- Dark skin = ancestral in humans – protects against Ultra-Violet radiation (UV)
But some UV – required – for synthesis of Vitamin D
Pale skin evolved – avoids Vitamin D deficiencies at higher latitudes
Skin colour closely related to regional levels of UV
Alleles at various specific pigmentation loci – closely associated with light skin
What is an example of human evolution occuring today?
Influence HIV/AIDS has on human evolution
What is the overview of HIV on current human evolution?
Some geneotypes make a person more susceptible to HIV compared to others
The more susceptible the reduced number of children compared to genes that offer resistance
How does population level of HIV impact evolution of resisitance genes?
In South Africa - 20% pop have HIV
Most common susceptible genotype - 0.8 children
Most common resistant genotype - 1.3 children
Other South African population lower amount of HIV
Most common susceptible genotype - 0.97 children
Most common resistant genotype - 1.1 children
South African population with higher amount of HIV
Most common susceptible genotype - 0.7 children
Most common resistant genotype - 1.38 children
There is stronger selection in populations where HIV is more prevalent
