Ch20: Human Evolution

*The Origin of Homo sapiens: Three hypotheses: Morphological Data* 1. The African Replacement theory predicts that morphologically all modern humans are more closely related to .... 2. also predicts that forms from Africa will be most closely related to ..... 3. does morphology support these ideas? *The Origin of Homo sapiens: Three hypotheses: Molecular Data from Modern Humans* 1. African replacement predicts what ? 2. does the data support this ?

*Morphological Data* 1. African Replacement predicts that morphologically all modern humans are more closely related to each other than any is to an archaic form 2. Also forms from Africa will be the most closely related to modern humans rather than local archaic forms 3. Morphology most supports these ideas *Molecular data from Modern Humans* 1. African replacement predicts that all modern non-African gene sequences will branch from within the African sequences 2. the data mostly supports this idea

*The Origin of Homo sapiens: The African Replacement Hypothesis* 1. what is it also known as 2. where did H.Sapiens evolve then migrate to 3. interaction to H.erectus/neanderthalensis 4. earlier homo species genes and modern populations? *The Origin of Homo sapiens: Hybridization and Assimilation* 1. where did modern humans evolve then migrate to 2. interaction to H.erectus/neanderthalensis 3.4. earlier homo species genes and modern populations? *The Origin of Homo sapiens: Multiregional Evolution* 1. where did modern humans evolve 2. interactions among populations, different species? 3. what is the modern gene pool a mixture of

*TThe African Replacement Hypothesis* 1. "Out of Africa Model" 2. H. Sapiens evolved in Africa then migrated to Europe, Asia and beyond 3. Replaced H.erectus/neanderthalensis without interbreeding 4. No genes unique to earlier homo species persist in modern populations *Hybridization and Assimilation* 1. Modern humans evolved in Africa then migrated to Europe, Asia and beyond 2. Replaced H. Erectus/neanderthalensis with interbreeding 3. Some genes unique to earlier Homo species persist in modern populations *Multiregional Evolution* 1. Modern humans evolved concurrently in Africa, Europe, Asia and beyond 2. Enough gene flow (interbreeding) among populations to remain a single species 3. Modern gene pools derive from a mixture of local and distant archaic populations

The Ape Phylogeny: Morphological Evidence Humans and ape share many synapomorphies (common derived characteristics) including 1. 2. 3. 4. 5.

1. Absence of tail 2. Relatively large brains 3. Greater flexibility at hips/ankles + wrist/thumb 4. More erect posture 5. Changes in arms/shoulder

*The Ape Phylogeny* 1. Darwin proposed humans were derived from the same Homininae lineage as 2. was he right? what evidence supported this 3. What is the controversy in determine our closest evolutionary relatives? 4. Did humans evolve from monkeys ? 5. which are most closely related to

1. African great apes 2. yes, molecular + morphological evidence 3. where we fall compared to chimps, bonobos and gorillas, which are are closet evolutionary relatives 4. no, we evolved from a common ancestor to modern chimps, bonobos and gorillas 5. chimps

*The Origin of Homo sapiens: Here's a different line of evidence using allelic variation on chromosome 12* 1. how does African population compare to non-African populations 2. diversity related to distance from Africa 3. what does each region show 4. similar pattern to what 5. which origin of homo sapiens hypothesis does this data support

1. African population show much greater diversity than non-African populations 2. Diversity declines proportionally with distance from Africa 3. Each region shows a subset of alleles from those present in the previous regions (closer to Africa) 4. Similar to founder effect pattern 5 All these data tend to support the African Replacement model

Darwin and human evolution

1. Darwin avoided talking about it in first book 2. wrote in second book the Descent of Man

Overview 1. how does genetic diversity among modern humans compare to other apes 2. where does most diversity occur 3. how can you recover geographic divergence among modern humans

1. Genetic diversity among modern humans is quite low compared to other apes 2. Most diversity is among individuals within populations, rather than between populations (or races) 3. But if you use lots of SNP data you can recover geographic divergence among modern humans

What is the percentages of the following sequence divergence across the whole genome (the % of difference in base pair sequence in 100bp chunks) 1. human vs chimp 2. human vs gorilla 3. human vs Orangutan 4. how much of the human genome can't be aligned to chimpanzee 5. how much of the human genome can't be aligned to bananas, how much can, what does this mean for sequence divergence What is the current divergence time estimates combining molecular and paleontological data for the following pairs 6. human vs chimps 7. human/chimp vs gorilla 8. apes vs old world monkeys

1. Human vs Chimp = ~1% divergence 2. Human vs Gorilla = ~1.5% divergence 3. Human vs Orangutan = ~3.5% divergence 4. 4% 5. ~40% of human genome can't be aligned to bananas - that means 60% can and in those regions average sequence divergence is ~40% 6. human vs chimps: 5.4 +/- 1.1 mya 7. human/chimp vs gorilla: 6.4 +/- 1.5 mya 8. apes vs old world monkeys: 23.3 +/- 1.1 mya

*The Origin of Homo sapiens: Three hypotheses- what is the Implication of Different Models* 1. if African replacement is true then.... 2. if hybridization or multiregional evolution are true, then....

1. If African replacement is true then all modern human variation (however subtle) develop due to geographic differentiation within the last 100,000-200,000 years 2. If hybridization or multi regional evolution are true, then modern variation represents a mixture of recent and ancient geographic differentiation

*The Early Human Fossil Record:* - Human chimps and bonobos shared a common ancestor about 5-7 mya. Fossils determined what about the nature of this ancestor 1. 2. 3. 4. 5. 6.

1. Knuckle walking 2. Broad fruit based diet 3. Range of different habitats 4. Tools to obtain/process food 5. Culture (also a feature of orangutans) 6. Social behavior - Chimps - male dominated, strategic alliances, violent - Bonobos: female dominated, social bonds, less violent

Why do different genes show different phylogenetic relationships 1. 2. 3. 4. What is incomplete lineage sorting? 5. why is incomplete lineage sorting most common in non-coding regions

1. Some genes evolved at different rates in different species 2. Some genes are horizontally transferred (not so common in primate though) 3. Some genes undergo incomplete lineage sorting 4 *incomplete lineage sorting*: when the combination of polymorphism at a locus, genetic drift + speciation causing descendant species to lose different ancestral alleles throwing off the gene tree's branching pattern from the true species tree pattern 5. because coding regions create proteins and are most subjective to selection/more constraint on coding regions with negative/purifying selection that alters diversity

1. how does the genetic difference among apes and even primates compare to other branches in the tree of life 2. how are the differences among humans

1. are small compared to other 2. The genetic differences among humans are even more subtle

*The Early Human Fossil Record:* 1. humans belong to a lineage that is 2. what are the two options of how the lineage evolved, which is the winning hypothesis 3. Over the last four million years, multiple species (up to five at a time) have coexisted in Africa. What we can conclude about the Homo sapiens

1. culturally + evolutionarily flexible 2. two options - progressive evolution of a single lineage - evolutionary radiation - winning hypothesis 3. conclude Homo sapiens is the sole survivor among diversity of species from an otherwise extinct radiation of bipedal African hominins

*gene tree vs species tree* 1. are they they same thing? 2. how are they different 3. why might a gene analysis produce a tree that is different than the "true" species tree

1. do not equal each other 2. Species tree show diverging groups while Gene tree show a mixture of both 3. the history of the gene might be different than the history of the species; ex horizontal gene transfer

*The Ape Phylogeny* 1. early molecular tests were use to 2. where did the data place the split between humans and apes, did this resolve the confusion 3. what is the current estimate, how does it compare to the early one?

1. generate antibodies in rabbits that react to human serum albumin, then test the response to other primate serum albumins to see if there is a reaction - expected that we would react most strongly to those most similar to human 2. The early data placed the split at ~5 mya, but didn't resolve the polytomy (A section of a phylogeny in which the evolutionary relationships cannot be fully resolved) 3. The current estimate is 5-7 mya (the original was pretty close!)

*The Origin of Homo sapiens: Three hypotheses: Molecular Data from Ancient Humans* 1. genomes are sequenced from what 2. the ancient split between modern humans and Denisovans/Neanderthals occurs across what 3. what was measured 4. what percentage of modern non-African genome derived from Neanderthals and modern Melanesian genome came from Denisovans were found in H. sapiens' genome 5. what does this data support

1. genomes were sequenced from DNA in preserved fossils. 2. across the whole genome 3. measured how much Neandertal and Denisovan DNA ended up in the Homo sapiens genome 4. Bottom line: 2.5% of the modern non-African genome derived from Neanderthals and 4.8% of modern Melanesian genome came from Denisovans 5. So these data support a version of hybridization/Multi-regional evolution rather than African replacement - the jury is still out

*The Origin of Homo sapiens:* 1. although there are five uncontroversially human species: Homo sapiens, homo neanderthalensis, homo heidelbergensis, homo erectus, homo ergaster- what is still debated 2. how long ago did modern humans appear in fossils 3. what was the initial range of modern humans 4. what was the exact progression, what are the three hypothesis 5. whatever their origin, it can be assumed that all living humans were

1. how many species they truly represent + how did modern humans/homo sapiens emerge from the others 2. 100,000 years ago 3. Africa + Middle East originally - later expanded throughout Europe and Asia 4. The African Replacement Hypothesis, Hybridization and Assimilation, Multiregional Evolution 5. extremely closely related to each other

1. the human genome is a 2. Genome wide what percentage of sequences feature incomplete lineage sorting 3. what percentage of sequence are humans more like chimps than gorillas

1. mosaic 2. Genome-wide: ~30% of sequences feature incomplete lineage sorting- where humans and chimps aren't the most closely related sequences 3. alternatively, humans are more like chimps than gorillas in 70% of sequences