L9 - Human Evolution & Expansion

Question 1

What biological groupings do humans fit into?

Answer 1

• Internal reproduction (like apes, mammals)
• Mammals
• Vertebrates (Evolved from Pikaia, something with a backbone)
• Eukaryotic cells: nucleus in cell
• Multicellular

Question 2

Where do humans fit into the tree of life?

Answer 2

• Kingdom: Animalia
• Phylum: Chordata
• Class: Mammalia (mammary glands, hair/fur, live births…)
• Order: primates (humans are the most related to chimpanzees)
• Family: Hominidae
• Genus: Homo
• Species: H. sapiens

Question 3

What characteristics do we share with other mammals?

Answer 3

• Mammary glands
• Hair/fur
• Live birth

Question 4

How far back do we have to go in the (Western) scientific literature to recognize that humans and apes are related?

Answer 4

1735: when it was first formally recognized that apes and humans were related
- Defined by Carl Linnaeus

Question 5

What is Lamarck’s theory of evolution?

Answer 5

• Thought that acquired characteristics can be inherited (giraffe necks)
• Thought that ancestral humans were likely tree dwelling, like apes today, and increasingly walked on the ground on two feet, until they became bipedal and lost the ability to climb trees

Question 6

What was Darwin’s theory of evolution?

Answer 6

• Natural selection

Question 7

Why was there a debate about human evolution?

Answer 7

• Lack of fossil record
• Had only found a fraction of the fossil record that we have today
• Until 1800s
  
  • No fossils found of ancient human species
  • Only a few stone tools

Question 8

When does the fossil record begins?

Answer 8

• 1820: first homid skull is found

Question 9

Fossils found in Indonesia?

Answer 9

• Home of the Orangutans
• Generally speaking, the tropics don’t preserve fossils very well, things tend to decay very quickly
• Found very primitive “human-like fossils”
  
  • Found the “missing link” between man and apes: HOMO ERECTUS

Question 10

Northern Kenya: fossil jackpot !

Answer 10

• Turkana Basin
  
  • Lake and river sediments = well preserved fossils
  • Good stratigraphy (can date things in relative layers)

Question 11

Was homonid evolution a straight line (one species became another, all are our ancestors)?

Answer 11

• No! A tree with many branches
  
  • Many homo sapiens co-evolved

Question 12

What is the base of the human tree? Australopithecus

Answer 12

• “Lucy”: bi-pedal, ape like
• Small brains, but some made and used tools
• Change in diet
• Greater sexual dimorphism (males and females look more different)
• Habitat: Africa
• Timeframe: 4.2 - 2 MYA

Question 13

The First Homo: Homo Habilis

Answer 13

• Brain is getting bigger, smaller teeth
• Definitely made stone tools
• Habitat: Africa
• Timeframe: 2.4 - 1.5 MYA

Question 14

Homo erectus - most successful human species identified to date

Answer 14

• Believed to be the first to leave Africa
• Big brains, tools, hunters
• Started to undergo social and cultural types of evolution (fire, art, speech…)
• Habitat: Africa, East and West Asia
• Timeframe: 1.9 MY - 150 000 years ago

Question 15

Later Homo lineages…

Answer 15

• Homo antecessor
• Homo heidelbergensis
• Homo florensis (the hobbit)
• Homo nadeli
• Homo luzonensis
• Homo rudolfensis
• Homo longi?
• Homo bodoensis?

Question 16

Homo Neanderthalensis

Answer 16

• Sister species to us
  
  • We both evolved from a single common ancestor
  • Neanderthals are not our direct descendants, although we share a little bit a DNA
• Had clothing, stored food, had art, had healthcare…
• Interbred with Homo sapiens
• Survived many ice ages
• Habitat: Europe, central Asia
• Timeframe: 400 000 - 30 000 years ago

Question 17

Why did Homo Neanderthalensis go extinct?

Answer 17

• Homo Neanderthalensis and Homo Sapiens were too similar and one had to outcompete the other
  
  • Genocide??

Question 18

Who are the Denisovans?

Answer 18

• Another sister species to humans
• First hominids we sequenced DNA from
• No skull identified to date
• Habitat: Western and central Asia
• Timeframe: 700 000 - 15 000 years ago

Question 19

Homo Sapiens: winners !!

Answer 19

• Only extant species in the Homo genus
• Must have developed traits that made us better competitors than our counterparts
• Skull morphology has changed distinctly over time
• Evolved in Africa and left ~ 185 000 years ago
• Interacted with other Homo species (i.e., outcompete them and killed them off, interbred)
• Habitat: originally Africa, current global distribution
• Timeframe: 300 000 - today

Question 20

What enabled/drove the diversification of the human lineages?

Answer 20

• Physical and technological changes opened up new niches
• Developing larger brains: intelligence !!
• Natural selection
• Physiological evolution that allow humans to better live in certain environments (ex: bipedal)
• Changes in climate - favourable periods that allowed expansion?

Question 21

Morphological traits

Answer 21

• Until recently, the identification of the human species depended solely on morphological traits
  
  • Fossil record is very fragmented
  • Difficult to distinguish chronospecies
  • Difficult to tell apart natural variation within species from differences separating species

Question 22

What are the challenges that arise when using DNA to identify species?

Answer 22

• It’s tricky to get DNA out of a fossil
• Half-life of DNA = 521 years
  
  • For reference, neanderthals went extinct about 20,000+ years ago

Question 23

What is ancient aDNA?

Answer 23

• Current theoretical upper limit for analysis: 1.5 MY
• aDNA sequenced to date: 430 000 years (early Neanderthal)
  
  • Could only sequence 0.1% of the entire genome

Question 24

Ancient aDNA: How?

Answer 24

If DNA breaks down significantly over time, how can we analyze sequences far past their half-life?
- PCR: lets us amplify very tiny samples
- Then, we need to reassemble the snippets of DNA back into the long reads of DNA
- We use Homo sapiens as a reference/guide as to where some of these snippets should go and how they should fit together

Question 25

aDNA - mistakes happen :(

Answer 25

- Modern contaminatio

Question 26

Neanderthal Genome Project

Answer 26

- International effort to sequence the entire genome of H. neanderthalensis from two bones - Took 4 years (vs 13 for Human Genome Project), and had to sort through degraded and contaminated aDNA

Question 27

What are the methodologies of the Neanderthal Genome Project?

Answer 27

- DNA sequencing struggles with contamination - Take samples from teeth/mouth - least amount of contamination here

Question 28

Neanderthal Genome Project - Discoveries

Answer 28

- H. neanderthalensis likely started with a very small founder population of 3000 individuals. - May have developed language like us - H. sapiens -H. neanderthalensis hybridized and produced fertile offspring!

Question 29

The Denisovans

Answer 29

- Denisovans interbred with H. Sapiens and H. neanderthalensis - As much as 17% of the genome of the Denisovan girl is from a Neanderthal genome - Particularly pronounced in East-Asian populations - Total amount of Denisovan DNA in modern human genomes = 0.5% - 1.1%

Question 30

Most recent developments with aDNA?

Answer 30

- 2017: sucessfully extracted aDNA from the teeth of 90 ancient Egyptian mummies - Revealed that people who made mummies are not the same people who inhabit Egypt today - Most closely related to people from the near east

Question 31

What is eDNA?

Answer 31

- Environmental DNA - Organisms are constantly shedding DNA into their environment (skin cells, bacterial cells, excretion; feces; coughing) - Unlike RNA which breaks down pretty quickly, DNA can be relatively stable, particularly when its preserved in sediments - eDNA techniques have been applied to sediment sites of ancient human habitation - like caves