Lecture 3 Flashcards
Where did humans originate?
Two main ideas:
- anatominally modern humans (AMHs) evolved from H. erectus in multiple locations, and then gene flow occured between different populations - multiregional model
- AMHs first arose in Africa and spread from there, replacing other hominin populations e.g. Neanderthals etc. - out of Africa model
The earliest known AMH
These are thought to be the earliest - lower jaw bone
This analysis shows that the shape of the molars - various different species that are compared
Neanderthals and other homo species- blue area - specimens found that are anatomically modern humans
Shape of molars fit with other modern humans
Can look at stone tools that have been found at different sites around the world
Linguistics/ phonemics
Atkinson (2011) phonemic diversity supports a serial founder model of language expansion from Africa
Studied 504 languages
Phoneme - basic unit of sound
Diversity greatest in Africa
Data best fit model where origin is in Africa
Genetic evidence for the origin of humans
- Compared mtDNA (pros and cons) from placentas of 147 people and diverse geography
- Very laborious molecular technique - restriction mapping
- Genetic evidence data back to mid 1980s, tried to take mitochondrial DNA from various modern day humans with diverse geography
- Mid 1980s- lots of techniques weren’t available, worked with mitochondrial DNA most cells have many copies of mitochondria in it- mitochondria is maternally inherited
- They did restriction mapping - cut the DNA where they see the sites
Cann et al. findings
Looked at mitochondrial DNA divergence and the diversity within the populations
Figures show the percentage of diversity across continents
African populations have more diversity than elsewhere
They tried to work out the time for the most recent common ancestor
They estimated/ assumed that mitochondrial DNA evolved at a clock rate
They estimated that the common ancestor of all of the sequences probably lived 340 - 3000 years ago
From that, they speculated that all present day humans/ descendents from an African population
Also concluded that some of the early homo erectus specimens have not contributed to modern day mitochondrial regions - Asian homo erectus populations are not our ancestors
Timeline is consistent with out fossil records- data should be treated cautiously
1991 follow up mtDNA paper
Part of the motivation- recieved a few critisms for this at the time
One of the critisisms- small sample size, restriction mapping rather than actual DNA sequences
Criticised over their method - wasnt a full statistical test and couldn’t be calibrated
1991 follow up mtDNA paper (ii)
- Sequence data from 135 people
- Newer tree-building approach
- African branches are deeper (older) and Non-african branches shallower (more recent)
- Rate estimated by comparison between human- chimp mtDNA
- Estimated that common ancestral sequence was from an African 200KYA
Reaction to Vigilant et al
Templeton claimed a better tree (same data) supported non-Africans being basal (older)
Other critics said data being inconclusive but might support out of Africa
Mitochondrial studies: round up
Methods improved- both in terms of collecting data and statistically
All show that diversity is greatest in African populations
All show that the deepest branches are African
All support the idea that humans evolved in Africa then spread to other parts of the world
All support the idea that humans evolved in Africa and then spread to other parts of the world- some interpretations of the data remained controversial
But
Intepretations of the data remained controversial e.g. templeton critisisms
Mitochondrial DNA is a tiny fraction of the genome
The Y chromosome
Sequences 3 Y chromosome genes total length 64Kbp in 70 men
Y chromosome only found in males (so paternally inherited ) completely different evolutionary history to mtDNA
similar patterns to the mtDNA studies
Most recent common ancestor 59 (40-140) KYA
Branch with African and non-African lineages 40 (31-79) KYA
Draft from whole genomes
1000 genomes project
Whole genomes of 179 people from 3 populations and large proportions of genome from a further 697 people (7 populations)- counted up total number of SNPs combined in each population
African population had more diversity than European - consistent with out of Africa theory
More recent genomic data
Consistent with the out of Africa model- better data - difference between Y and mitochondria gets smaller
Considering the two main models
Fossils indicate earliest AMHs were present in Africa up to 300KYA
Stone tool data not very conclusive
Linguistic data supports African origin of language
Genetic data supports Out of Africa well
