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Evolution of Lactase Persistence
Alan R. Rogers
November 22, 2015
Outline
I Lactose, lactase, and lactase persistence
I Evidence of a selective sweep
I Prehistory of Europe
The trouble with fresh milk
I Contains the sugar lactose
I Digesting lactose requires the enzyme lactase
I Most humans don’t produce it after age 5.
I Fresh milk gives them gas and diarrhea.
I 8000 years ago, all humans had this problem.
Lactase persistence
I Some modern humans produce lactase throughout life.
I Digest fresh milk as adults.
I Caused by mutation near lactase gene.
I When and where?
Distribution of lactase persistence (dark blue) Within countries, lactase persistence more common inpopulations that drink milk
Lactase persistence in Europe
I ModernEuro-peans
I Dashes:Funnel-beakerculture
Outline
◦ Lactose, lactase, and lactase persistence
I Evidence of a selective sweep
I Prehistory of Europe
Evidence for a selective sweep
I In Europeans, persistence allele surrounded by a million basesof LD.
I Indicates strong selection.
I Statistical tests reject the drift hypothesis (Bersaglieri et al2004)
I Increasing for ∼10,000 years (Coelho et al 2005).
LD surrounds lactase gene in Europe
Huge block of LD around lactase allele in Europe
(Nathan Harris)
I Rows are differentSTRs
I Lactasepersistence allele:haplotype TA.
I Has reduced SNPvariation,
I Indicates recentorigin.
I Age: 7,450 or12,300 years(depending onassumptions)
Outline
◦ Lactose, lactase, and lactase persistence
◦ Evidence of a selective sweep
I Prehistory of Europe
Lactase persistence in ancient Europeans
T is lactasepersistence allele
Appeared in Europeby 2500 BC
(Kruttli et al 2014)
What washappening there5000 y ago?
Modern Europeans derive from 3 ancestors
EEF: Early EuropeanFarmers
WHG: WesternHunter-Gatherers
ANE: Ancient NorthEurasians
(Lazaridis 2014)
Old Europe
I Expanded into Europe fromMiddle-East and Anatoliabeginning 7000 bp.
I Earliest European farmers.
I Lactose intolerant.
Otzi, the Iceman
I 3300 BC on border betweenItaly and Austria
I Hair had high levels ofcopper and arsenic—a metalsmith.
I Last meals: chamois and reddeer mean, and einkornwheat
I Lactose intolerant.
Long house
Sculpture The Yamna culture: pastoralists
Mare’s milk
I One kg of mare’s milk has 190 Calories of fat and protein 250Calories of lactose.
I With 5 kg per day yield one mare feeds two lactase persistentchildren.
I Less that one non-lactase-persistent child.
I Lactase persistence more than doubles food supply with onesimple mutation.
I This advantage cannot be appropriated by others.
Indo-European expansion
Indo-European languages Tocharian
Modern Uighurs Corded ware culture
2400 BC
Overran Europe
Possibly introducedIndo-Europeanlanguages
And maybe also lactasepresistence
Study of Mathieson et al 2015
I DNA from 83 ancient Europeans.
I Track changes in allele frequencies over time.
History of evolution in Europe
Lactase persistence begins in Europe around 4000 BP.
Summary
I Recent adaptive evolution in lactase persistence.
I Appears in Europe about 5000 y ago.
I May have arrived with Indo-Europeans.