Human Evolution I

Question 1

True or false: Phylogenetics says we are apes.

Answer 1

True

Question 2

List the synapomorphies of apes. (6)

Answer 2

o Large brains
o Absence of tails
o Erect posture
o Greater flexibility of hips and ankles
o Increased wrist/thumb flexibility
o Changes to shoulder and arm structures

Question 3

List the synapomorphies of great apes. (4)

Answer 3

o Elongated skulls
o Enlarged brow ridge
o Shortened, stout canines
o Enlarged ovaries and mammary glands

Question 4

Who are our (humans’) closest living relatives?

Answer 4

Chimpanzees and bonobos

Question 5

When did humans diverge from chimps and bonobos?

Answer 5

~5 million years ago

Question 6

What are the four synapomorphies that make Hominids different from other Great Apes?

Answer 6

o We started to walk on two legs
o Our brains got very large
o We lost our hair
o We started to use tools

Question 7

How many Homo lineages originated and then migrated out of Africa?

Answer 7

At least 3

Question 8

When did Homos start migrating out of Africa?

Answer 8

2 million years ago

Question 9

What is the multiregional model for the origin of humans?

Answer 9

o H. erectus migrated out of Africa ca. 2 million years ago
o Diverging populations hybridized giving rise to H. sapiens
o Single old migration out of Africa

Question 10

If the multiregional hypothesis were true then… (3)

Answer 10

o Multiple and perhaps simultaneous origins of H. sapiens in Africa, Europe and Asia
o Common ancestor to all humans should be old (2 million years)
o Humans should show equal genetic diversity around the world

Question 11

What is the African replacement model for the origin of humans?

Answer 11

o Three Homo spp. Migrations out of Africa
o H. sapiens migrated out of Africa 40-60 thousand years ago, replacing H. neanderthalensis and perhaps also H. erectus without hybridization

Question 12

If the African replacement hypothesis were correct then… (3)

Answer 12

o Single origin of H. sapiens in Africa
o Common ancestor to all humans should be young and distinct from H. erectus and H. neanderthalensis
o Non-African modern humans should represent a subset of the genetic diversity found within African humans

Question 13

What is the leaky replacement hypothesis of human origins?

Answer 13

H. sapiens migrated out of Africa 40-100 thousand years ago, replaced AND hybridized with H. neanderthalensis

Question 14

Which hypothesis is the winner?

Answer 14

Leaky replacement

Question 15

What are the five pieces of evidence in support of the leaky replacement hypothesis?

Answer 15

• Ancient Homo species dispersed out of Africa ca. 1.8 MYA and colonized Europe and Asia
• Earliest H. sapiens fossils (195,000 years ago) are from Ethiopia
• Phylogenetic analyses show that the common ancestor to all non-African modern humans are African modern humans
• Genetic diversity in non-Africans represents a narrow subset of the genetic diversity found in Africa
• Comparison of European Neanderthal nuclear DNA with human populations
  o 1-4% of non-African modern human DNA was more closely related to Neanderthal DNA than African modern human DNA
  o Small amount of interbreeding between H. sapiens and H. neandrathalensis as humans migrated out of Africa