Evolution: changes in allele frequencies over time
4 forces of evolution
o Mutation (only source of new variation)
o Selection (acts to diverge populations directionally)
o Drift (act to diverge populations randomly)
o Migration (acts like genetic glue)
Epidemiology: the science of disease occurrence and transmission
Human babies drink mama’s milk for the first 6 months
o Babies drink milk but adults don’t
Ex: cats. Meow.
Basic primitive condition: adult mammals are lactose intolerant
This is because there needs to be a point where the babies
stop drinking their mothers milk
Lactose: milk sugar
Lactase: enzyme that digests lactose into usable parts
Lactose intolerant: “normal” for humans but the derived trait is lactase persistent
o Aka: mutated allele (lactase persistent (+)) lactose tolerant. Can digest
milk. All babies are this.
o Vs normal allele (lactase (-)) lactose intolerant. Body can’t digest milk and
the bacteria digests it instead.
Ex: Asians, blacks, Native Americans – high % of people are
Why are there hotspots?
Migration? No! Look at a map. Random peaks and stuff.
Don’t match migration patterns.
Sexual selection? No! Don’t wana mate with someone who
can drink milk.
Natural selection? YEA! Food value, water content, more
o Can do better than others
o BUT what environment would favor ability to digest
Pastoralism: Economy that relies on cattle, sheep, goal, CAMEL, etc.
o Get milk, meat, blood from them (mainly milk and blood)
o Even if you can’t drink their milk it’s still super helpful
o Helpful for places with little water
o Kids take animals in the morning, take care of them, then bring them back
Sheep: little boys and little girls take them out
Cattle: teen guys
Camel: young men
o ANIMALS ARE EVERYTHING TO THEM :D
Ex: Hlusko in Ethiopia, Tanzania Lactase persistence = around world based on selection
o Only in Europe?
Because of rickets? Need milk to help deficiency – nahhh
o If you don’t live around animals who produce milk then there is no
selection for lactase persistence
o Lactose intolerance is the natural condition of most adults
the culture of the society is the thing that naturally selected for this
LCT gene –
o Perfect correlation between lactase persistence and having at least 1
alleles for this
Some people can digest milk better than others (homo vs hetero,
this gene is “dominant”)
o 9-10kya there was a cultural environment to select for this
People focused in Europe but Africa too! (4-5kya)
o There are different mutations that lead to the same thing
o Convergent evolution! :D
o 19% more offspring for people who are lactase persistent
Inherit 2 kinds of information from ancestors: genetic & cultural
o Ex: more people with larger brains because there are complex social