L9 - Human Evolution & Expansion Flashcards
(31 cards)
What biological groupings do humans fit into?
- Internal reproduction (like apes, mammals)
- Mammals
- Vertebrates (Evolved from Pikaia, something with a backbone)
- Eukaryotic cells: nucleus in cell
- Multicellular
Where do humans fit into the tree of life?
- 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
What characteristics do we share with other mammals?
- Mammary glands
- Hair/fur
- Live birth
How far back do we have to go in the (Western) scientific literature to recognize that humans and apes are related?
1735: when it was first formally recognized that apes and humans were related
- Defined by Carl Linnaeus
What is Lamarck’s theory of evolution?
- 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
What was Darwin’s theory of evolution?
- Natural selection
Why was there a debate about human evolution?
- 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
When does the fossil record begins?
- 1820: first homid skull is found
Fossils found in Indonesia?
- 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
Northern Kenya: fossil jackpot !
- Turkana Basin
- Lake and river sediments = well preserved fossils
- Good stratigraphy (can date things in relative layers)
Was homonid evolution a straight line (one species became another, all are our ancestors)?
- No! A tree with many branches
- Many homo sapiens co-evolved
What is the base of the human tree? Australopithecus
- “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
The First Homo: Homo Habilis
- Brain is getting bigger, smaller teeth
- Definitely made stone tools
- Habitat: Africa
- Timeframe: 2.4 - 1.5 MYA
Homo erectus - most successful human species identified to date
- 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
Later Homo lineages…
- Homo antecessor
- Homo heidelbergensis
- Homo florensis (the hobbit)
- Homo nadeli
- Homo luzonensis
- Homo rudolfensis
- Homo longi?
- Homo bodoensis?
Homo Neanderthalensis
- 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
Why did Homo Neanderthalensis go extinct?
- Homo Neanderthalensis and Homo Sapiens were too similar and one had to outcompete the other
- Genocide??
Who are the Denisovans?
- 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
Homo Sapiens: winners !!
- 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
What enabled/drove the diversification of the human lineages?
- 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?
Morphological traits
- 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
What are the challenges that arise when using DNA to identify species?
- 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
What is ancient aDNA?
- 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
Ancient aDNA: How?
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
