Human Evolution

Question 1

What superfamily are humans a part of? What does it contain?

Answer 1

Hominoidea - group contains all living and extinct apes and human ancestors

Question 2

What morphological synapomorphies distinguish Hominoidea from other primates?

Answer 2

1. lack of tail
2. Upright trunk
3. High joint mobility
4. widely spaced shoulders

Question 3

What is the Great Apes (Hominidae) classification and how many species/genera make it up?

Answer 3

The great apes (Hominidae) is a subfamily made of 8 extant species in 4 genera + humans

Question 4

What morphological synapomorphies distinguish Hominoidea from Hominidae? (4)

Answer 4

1. Elongated skull
2. Enlarged brow ridge
3. Shortened stout canines
4. Enlarged ovaries/mammary glands

Question 5

What is the closest living relative to humans?

Answer 5

Chimpanzees

Question 6

With which species are humans closer than chimpanzees to at roughly 20% of loci? How can this be explained?

Answer 6

Gorillas are closer at 20% of loci, which can be explained by incomplete lineage sorting, as coalescence of those genes could have happened much earlier than the speciation, with humans diverging from chimpanzees before gorillas for certain genes

Question 7

Why would a polymorphism arise?

Answer 7

Drift - it is random

Question 8

What evolutionary force is responsible for incomplete lineage sorting?

Answer 8

Genetic drift

Question 9

In which branch of the gene tree of humans, gorillas, and chimpanzees would a polymorphism be maintained in the genes where gorillas have a closer relation to humans?

Answer 9

In the branch after gorillas speciate, there will still be polymorphism between humans and chimpanzees before they genetically diverge

Question 10

In what kinds of branches would polymorphisms be more or less likely to be maintained?

Answer 10

In long, narrow/small populations, polymorphisms would be less likely to be preserved. They would be more likely to be preserved in in shirt, wide/large branches

Question 11

What are hominids?

Answer 11

Our closest relatives (all extinct)

Question 12

Is human evolution linear?

Answer 12

No

Question 13

When did the hominem lineage arise? What environmental trend arose concurrently?

Answer 13

roughly 6m years ago there was a period of environmental change and cooling

Question 14

What are the two hypotheses of the role of environmental change in humans?

Answer 14

1. Savannah hypothesis - cooling temperatures and changes in seasonal patterns caused a shift from tropical forest to savannah
2. Environmental Variability hypothesis - instead of evolving to a single environment, humans adapted to cope with changing environments

Question 15

What Savannah hypothesis traits were observed?

Answer 15

Bipedal Locomotion and Loss of large canines

Question 16

What were the hypothesized reasons for bipedal locomotion?

Answer 16

1. More efficient than knuckle walking
2. Keeps hominins cool in sunlight

Question 17

What is the hypothesized reason for loss of large canines?

Answer 17

Different diet

Question 18

Which human evolution hypothesis is more supported?

Answer 18

The environmental variability hypothesis

Question 19

What fossil record is there of the environmental variability hypothesis?

Answer 19

Remains have been found in a variety of habitats, and some species occupied multiple habitats

Question 20

How long have humans been dominant species for?

Answer 20

12K years

Question 21

What is the clade of humans called?

Answer 21

Hominin

Question 22

What characteristics do early hominins share?

Answer 22

Small cranial capacity and some limited capacity for upright locomotion (some were still arboreal - toed)

Question 23

What challenges are there to determining the evolutionary history of Hominins?

Answer 23

1. It is close to the split with chimpanzees
2. Geological forces have distorted some fossils

Question 24

How long ago did the hominin clade appear?

Answer 24

7mya

Question 25

How long ago did archaic hominins live?

Answer 25

4.2-1.9 mya

Question 26

How are archaic hominins differentiated from modern humans?

Answer 26

They had thick skulls, prominent supraorbital ridges, and a lack of a prominent chin

Question 27

How early was tool use discovered?

Answer 27

3.4mya (widespread 2.6mya)

Question 28

What side branch group of Hominids became fully extinct and were characterized by huge muscle attachment regions on the skull and large teeth

Answer 28

Megadont archaic Hominins

Question 29

What are the earliest members of the genus homo? How long ago did they appear?

Answer 29

Transitional hominins - 2.3mya

Question 30

Describe the transitional hominin craniums

Answer 30

They had smaller brain sizes than premodern hominins, but bigger cranial capacities than archaic hominins

Question 31

Premodern hominins (2mya) had what characteristics?

Answer 31

1. Body plan similar to humans 2. Taller than transitional/archaic hominins + larger brain 3. used tools 4. used fire to cook

Question 32

Humans share a most recent common ancestor 800K-500K years ago with which species?

Answer 32

Neanderthals and Denisovans

Question 33

How long ago were Indonesian side branch tiny hominins expected to go extinct?

Answer 33

12K years ago

Question 34

What are the two alternative models to modern human transition?

Answer 34

1. Multiregional Model -humans migrated out of Africa ~2mya, and evolved in Europe, Asia, and Africa with enough gene flow to maintain a single species 2. Out of Africa Model - 3 waves of colonization, Africa to Asia ->common ancestor migrates into Europe and Asia -> Homo Sapiens arise in Africa as well and migrate around the world

Question 35

What phylogenetic predictions can be made under the multiregional hypothesis?

Answer 35

The common ancestor to humans should be very OLD (2MYA) - and humans will show equal genetic diversity around the world

Question 36

Which model for human transition is more supported?

Answer 36

The out-of -Africa Model

Question 37

What phylogenetic predictions can be made under the Out of Africa hypothesis?

Answer 37

1. There is a single origin of H. Sapiens in Africa 2 . Common ancestor to all humans should be relatively young and distinct 3. Non-African humans represent a subset of genetic diversity of African humans

Question 38

What are the 5 supports to the Out-Of-Africa Model?

Answer 38

1. Fossil evidence of gradual divergence of humans in Africa (Ethiopia) 2. Archeological evidence suggest toolmaking started in Africa 3. Phylogenies suggest non-African individuals arose from African populations (200K years ago -Mitochondrial Eve) 4. SNP analyses of the gene support Out-Of Africa 5. Genetic diversity declines with distance from Africa

Question 39

When did H. Sapiens migrate?

Answer 39

~60K years ago

Question 40

How did genetic lineages mix between different Hominin groups?

Answer 40

Hybridization was present ->introgression