Neolithic Revolution

Rapid changes over a few millennia - foraging to farming - large settlements; cities - written language: Sumer 3500 BC China 1500 BC - systematic thinking (philosophy)Are these changes too rapid to be produced by genetic evolution?

Large Communities: Cities

What factors have made this possible? - Large brain? - Language? - Mutual tolerance? - Religion? - Altruism?

Cultural Evolution

Learning from experience, Transmitting by observation and emulation Transmitting by language

Variation in cultures reinforces group identity

Rapid evolution of language diversity - about 7000 languages exist – half are unwritten - 96% spoken by only 4% of people - many becoming extinct

Natural Selection in Human Evolution

• Natural selection has central role in Darwinism• Has been inferred in changes since Chimp-Human LCA• Can this be shown specifically in human evolution?• If so, supports idea that human evolution has been Darwinian

Thalassemia

Reduce synthesis of globin chainsTwo forms α and βImbalance of chains causes abnormal haemoglobinAnaemiaCommon in East Mediterranean, across to S.E. AsiaLike sickle cell, carriers (heterozygotes) have greater resistance to malaria

The Milk Revolution

Not everyone can drink milk as adultsOne component of milk – lactose – is toxic to those adultsBabies can tolerate lactose up to age 7 - 8Lactose tolerance in adults occurs in some regionsIn these regions lactase enzyme continues to be active in adultsMutation in gene which switches lactase gene on or off

Distribution of Lactose Tolerance

Selection for Lactose Tolerance in Adults

Cows milk palatable if made into cheeseEvidence for cheese making 7000 years agoPottery with fine holes (sieve) which contained fatty residues from milkIf cattle reared for milk, mutation in humans to allow it to be drunk would be favoured Mutations selected in several regions – same effects on lactase, but genetic changes were differentEuropean mutation occurred about 7,500 years ago

Denisovans and Tibetans

Denisovans are descendants of H. erectus migrants in Siberia – fossils 50 Kya (Denisova is a cave)Now extinct but modern humans in SE Asia have 2% Denisovan DNATibetans have a gene (EPAS1) variant which is advantageous at high altitudes – appears to modify properties of haemoglobinGene region is identical to that found in DenisovansSuggest interbreeding between Denisovans and modern humans Then natural selection as Tibetan plateau colonised

Tay Sachs Disease

Mutation in HERA geneβ-hexosaminidase – removes toxic gangliosidesAffects brain development - lethalAshkenazi Jews – 1 in 3500 births are affected - I in 30 are carriersGiven lethal consequences, why is mutant form so relatively high?Probably due to “Founder Effect” – population was very small at some stage

Ghengis Khan’s Y ChromosomeAbout 8 % of men across Asia carry a specific Y chromosome typeDistribution suggests it originated about 1000 years ago in MongoliaArea sampled coterminous with maximum extent of Mongol empireHigh frequency suggests selectionWas this selection natural or social?Belief that Ghengis Khan and his male relatives fathered thousands of children

Qualitative and Quantitative Variation

Some differences in an individual gene produce recognisable differences in expression . Qualitative effectsBut many characters controlled by many genes and effects on single genes cannot easily be identified. Quantitative effects e.g. stature, behaviour, intelligenceAlso, expression influenced by environmental effectsCan genetic and environmental effects be separately be measured?Frequency distribution of such characters often that of the Normal Curve

Quantitative Variation Determining Genetic ComponentAssume that some part of observed variation is genetic and rest is environmentalGenetic component can be estimated from correlations between different types of relatives: - identical twins – differences are environmental within families - identical twins reared apart – differences between families - siblings reared together – genetic and environmental differences - siblings reared apart – environmental differences between families - parents and offspring - etcEstimates of genetic (Vg) and environmental (Ve) variationHeritability is Vg/(Vg + Ve), i.e. proportion of total variation which is genetic

Changes in Hairiness and Skin Colour

Early hominins moved from forests to open savannahExposed to harsh sunChange to hairlessness to allow sweating to keep cool except on head – some protection from sunThen to black pigmented skin to protest from UVBut migration to northern regions and lower levels of sunshine caused vitamin D deficiencySo selection to paler skin

Human Evolution and Lice

Infection by 3 types of lice - head - clothing (body) - pubicMitochondria DNA sequencing of head and clothing typesDiverged about 170 KyaSuggests association with use of clothesWas this associated with climate cooling at that time?Hairlessness probably arose much earlierIf wearing clothes began for H. sapiens in Africa, practice useful when migrating to colder north

What happened to the Neanderthals?

Neanderthals evolved in Europe from Homo erectus migrations out of Africa 1.8 MyaNeanderthals were large, had relatively large brains (1200c) and developed stone weapons H. sapiens followed 50 KyaBy 40 Kya Neanderthals had disappearedHumans had bigger brains and better tools – did they eliminate Neanderthals?Evidence of interbreeding. Modern European genome has 2-3% genome which is Neanderthal. Note that modern Africans have none.Or was climate change responsible?

Human Diseases and EvolutionChanges in humans

Cystic fibrosis - affects lungs; usually early death - recessive gene, carriers up to 1 in 30 among Europeans - high frequency for lethal mutation - possibly heterozygote advantage? (cf sickle-cell)

Smallpox - degree of genetically-based tolerance in Europeans - European colonisation spread virus - caused devastation in native Americans and Australian Aborigines

Human Diseases and EvolutionChanges in infecting organisms

Resistance in bacteria to antibiotics – multiple resistance (e.g. MRSA)Resistance to vaccines in virusesBug evolution can outrun human evolutionConstant search for new antimicrobial treatments

What will be future of human evolution?

Has human evolution been Darwinian? (Question in course title)

Or has much change been due to cultural (non-genetic) evolution?Particularly in last 20 Ky

But cultural transmission depends on mental abilityHumans are “wired for culture”