week 4 - evolution Flashcards
fossil basics
- Trace fossils (ichnology)
o Footprints
Imprints not necessarly accurate but do give us a lot of information about the species
o Coprolites, tracks, trails, nests - Perimineralisation and petrification
o Chemical process
o Minerals replaced - Moulds and casts
taphonomy
The what and how of fossilisation
- Why are some bones more common than others?
o Very common to find teeth (because survives more often)
o Heavy bones more likely to be fossilised
- Why are fossils not found everywhere
o Where matters (understanding habitat) eg rainforest too acidic for fossils
Geological time, stratigraphy and dating
Stratigraphy: how the layers in the earth are put together
Don’t need to remember all the eras but should be familiar with the eras
Cenozonic era
Not as simple as the deeper you go the older it is
* Shit happens (caves
* Dating is really complicated
* So there is lots of agreements with dating
how do you determine a species
Splitters
- Different species unless there is a convincing reason to untie them
o Variation = new species
Lumpers
- Same species unless there is a convincing reason to divide them
o Intra-species varitation normal
i.e. age; sex; disease; genetic variation
A lot of disagreement about this
Element of ego
* E.g. named a new species
interbreeding
- Different, related species can interbreed
- Often infertile
o But not always; can take 2Ma of separation for infertile hybrids - Hybrid zones: 10% of primate species engage in cross-species hybridization
- Hybrids can result in new species
We (homo sapiens) are proof of this
fossil remains are limited
- Complete skeletons are incredibly rare
- Usually find a mix of fragment bones and teeth
- Often impossible to link cranial and post cranial remains
o And they don’t always link
what defines the genus homo?
Original definintion of homo genus compared to previous genus:
- Small, ‘modern’ teeth
- Bipedal
- Tool use
- Brain size
what defines the genus homo?
small teeth
Comparatively our teeth are smaller
BUT
There in an older species (Australopithecus sediba (MH2)) in another genus with teeth smaller than some of the early human species
So not a clear dividing line
what defines the genus homo?
bipedal
- Upright posture/bipedality goes back to at least 7Mya with Sahelanthropus tchadensis
Far more likely our ancestors were upright - Like uranagtang
Goes back at least 7 million years
This upright body posture far predates our genus
what defines the genus homo?
tool use
- First homo species ~2.6 Mya
- ~3.3 Mya ‘Lomekwian’
o West Turkana, Kenya
o Kenyanpithecus platyops - ~3.4 Mya cut marks on bones
o Dikika, Ethiopia
o Australopithecus afarensis
Plently of other species can use tools - Stone tool far predate our homo genus
what defines the genus homo?
brain size
- Homo habilis 500cm3 low end
- Paranthropus robostus 550cm3
For a long time was considered an absolute cut off - This is not the case
- There is a trend towards bigger brain sizes
- No clear line to draw
Is our definition of Homo wrong and why all these problem with the Homo genus?
The year fossils were found is important
* Knowledge avaiable
Homo habilis
* Small brain
But had all the other aspects
Does this make them human
- There was an obsession of humans being more advanced (tool use) so wanted it part of our group
- So need all the evidence
Ancestry and interbreeding
- A lot of interbreeding
- We know this exists
Who evolved from who?
- Things get really messy
- Impossible to know
Unless in a modern situation can use genetics (this can still give different answers)
All of these species were alive at the same time
genetics and interbreeding
- H. sapiens show evidence of interbreeding with
o Denisovans
o H. neanderthalnsis
Shows how there was a constant flow of humans
o Unknows archaic European populations (Eurasians)
o Unknown archaic African population - H. neanderthalenisis and Denisovans interbred.
o Female remain from around 90 kya fund to have a a neanderthal m other and Denisovan father
Can see this with fossils
90,000 years ago
Very rare to catch
climatic factors:
adaptability and speciation
- Large climatic fluctuations when Homo genus evolved
- Strong links between climate and evolution of hominids
- If climate is variable/servere you might:
o Die out
o Move to a new area
o Adapt to different conditions - Hominin variability = environmental variability
- Not just anatomical but also cultural
o Suddenly find things like tool kits (a lot more variability)
Homo migration out of africa
The areas in the west with no fossils doesn’t mean hominids were not there just that the conditions were not optimunm for fossils
Places where multiple species where in one area
Huge range
It was thought for the longest time that homo hablis and erectus never left africa
did homo hablis leave africa?
- Small brains?
- In-efficient energetics?
- Challenging Northern Africa habitat
- Scavengers
- No current evidence
Theories as to whyy they couldn’t - They had reltively small brains compared to later forms
- Much shorter (stride length) more energy to travel
- Werent as efficent as moving
- North african climate to difficult to pass (desert)
- Scavengers of carcusses (not active hunters)
So likely they didn’t leave africa (no evidence)
Homo erectus: the first global species?
- Original considered all individuals:
o Energetically efficient, tall, bipeds
o Had increased brain size - Now known to be morphologically variable
o Plasticity? - Behaviourally more capable or adaptable?
- Active hunters?
o Migrating a lot easier - Luck?
o Lots of aspects coming together at once
Migration
- Very complicated
- Becoming more complicated in recent years
When looking at fossils don’t know their path
Used to think dates where too early
But in china more evidence of earlier dates
Therefore individuals must have left africa earlier than the times we have found because of the evidence else where
Huge areas where we don’t have fossils
New knowledge to tell us a bigger picture
Their movement takes time
They were just pushing the boundaries of what they knew
No set plan
Route could be literally anything
Homo floresienis
migration
- Some are saying their ancestor is homo hablis
- And this is an earlier time they left africa
On current evidence this seems unlikely
More likely ancestors are homo erectus
Neanderthals were adapted to European conditions, but died out after modern humans migrated to Europe
- Why?
A very successful species
The idea of them being brutish is mostly because they were found in victorian times and anything that wasn’t human was viewed as subhuman
We know we have a common ancestor (don’t know what this iss) -> sister species
Were adapted to europe
* But spread a long way across eurasia
Adapted very well to cold conditions
Have bigger brains than us
We interbred with them
At some point they eventually died out
* Big question of why this happened
what happened to the Neanderthals?
violence
- Did modern humans murder all Neanderthals?
- Evidence of inter aggression from bone injuries.
o Evendience of cut marks on biones with tools that homo sapiens made - BUT highly unlikely this caused Neanderthal extinction.
Evidence for conflict but no evidence that this was large enough to cause an extinction
what happened to the Neanderthals?
pathogens
- Infections disease from modern humans to Neanderthals
o tapeworm, tuberculosis, stomach ulcers & types of herpes - Neanderthal population weakened
We know that diseases passed from homo sapiens to Neanderthals
This would have served to weaken the population - Still unlikely that this alone caused extinction
Also other way round - But this helped us
