An evolutionary genetic approach
Genetics is just one approach for studying human evolution
It can delve into our recent and ancient past
A synthesis with other disciplines is likely to be most fruitful
when did early humans first appear?
- Humans and chimps/bonobos diverged about 6-7 million years ago (MYA)
- Anatomically modern humans (AMHs) probably appeared < 300 KYA
Clarifications and distinctions of humans
- Humans are the only surviving species in the genus Homo, but there were others (until quite recently) e.g. Homo neanderthalensis
- Closest relatives - chimps - diverged 6-7 million years ago
What does the human lineage consist of
any species that were our ancestors since the divergence between humans and chimps.
What are hominins
species that are closer to us than chimpanzees (not easy to define)
fossils are rare and often very incomplete and were sometimes predated by carnivores.
Fossil record species
human evolutionary genetics relies on history and linguistics etc.
Different disciplines can tell us going back to different lengths of time- historical records
Sahelanthropus tchadensis
Toumai – ‘hope of life’
- Possible ancestor
- Discovered in 2001
- Jaw and cranium fragments
-Some hominin-like features including flat face
-Mode of locomotion unknown - don’t know if it moves on 4 limbs or 2
Australopithecus afarensis
‘Lucy’
- Discovered in Ethiopa 1974
- Lived 3.2 MYA
- Laetoli footprints probably same species. Probably bipedal
- Sexually dimorphic. Weighed 25-50Kg, 1m-1.5m tall
- Lived in open savannah/grasslands
Australopithecus africanus
‘Taung Child’
- Discovered in Southern Africa in 1925
- Lived 2-2.9MYA
- More human-like than Au/ lucy . Afarensis and less sexually dimorphic
- First evidence that hominins arose in Africa
- Like A afarensis, this species was a gracile (lightly built) hominin
- More heavily built (Robust) hominin species are not thought to be our ancestors
Homo habilis (‘handy man’)
- Discovered by Mary and Louis Leakey in Olduvai, Tanzania (1960)
- Lived 2.3MYA
- Larger brain than Au africanus
- Perhaps first species to use stone tools
- Larger brain than au africanus
- Used to be considered the first hominin, but now placed in Australopithecus genus
H erectus used to be considered its descendent, but may have been around at same time
Homo erectus/erganser
“Turkana Boy” or “Nariokotome Boy”- regarded as a different species
- 1.9 MYA until ~135KYA
- Upright, tall (1.8m). Similar size and proportions to modern humans
- first to be Found outside Africa e.g. Java man, Peking man. H erganser used to be considered the African species and H erectus outside Africa. Now regarded as one species
- Earliest specimens outside of Africa are 1.8MYA
- Regarded as the first hominin ancestor
Homo hiedelbergensis
- Lived about 1MYA until 200KYA
- Larger brain than H erectus
- Ancestor of humans, Neanderthal man and Denisovan man (the genomic stars of this module)
- Not an ancestor, more a contributor (see Lecture 4)
Neanderthal man Homo neanderthalensis
- First discovered in Neander Valley, Germany (1856)
- Some specimens found earlier but not identified at the time
- Ranged across Europe 250KYA – 28KYA
- Same time as H sapiens
- Genome sequenced in 2010
- They were found in Europe at the same time as us
First anatomically modern humans (AMHs)
- Omo 1 lived 195KYA
Other well known specimens include Cro-magnon man – 1st specimens to be discovered; Middle Eastern specimens (90-130KYA); Lake Mungo, Australia (40KYA) and discoveries in China and Borneo (35-45KYA)
- Irhoud fossils near Safi in Morocco, are now thought to be considerably earlier
- Paper in Nature in June 2017 dated them as being from 315KYA
- We are constantly having to re-evaluate what we know about human evolution
What makes us human?
Some phenotypes are not shared with other great apes but may have been present in extinct hominins
- bipedalism
- ability to make fire
- clothing
- enlargened brains
- cooked food
- naked skin
How do humans have unusual life histories
- Growth spurt seen during Adolescence
-Female age structures in menopause - related to kin selection and helping offspring reproduce
Other kinds of genetic differences: Gene loss and gene gain
- There are only about 60 genes ‘new’ to humans
- Brain and testes expressed genes especially common
- Some genes have been lost
- Some of these changes are shared with Neanderthals
Other kinds of genetic differences: Gene family expansion
These can occur when whole segments of chromosomes get duplicated and so genes in those regions have multiple copies per genome.
Mutations in the individual genes mean that different members of a gene family can eventually have different functions
Examples of genes with multiple copies in humans, relative to great apes
Number in brackets refers to variation between human populations
Other kinds of genetic differences: Differences in coding sequence
100,000 of the human-chimp differences are in coding regions of genes
40,000 result in changes in amino acid
- Half on lineage leading to humans; ~1 per gene
- Many will no have affect on phenotype
Only around 100 differences between humans and our closest extinct relatives, Neanderthals and Denisovans
