human evolution Flashcards
what are the nearest relative
chimps
shared traits are due to
- shared common ancestor
- convergent evolution
Gigantopithecus
• Roamed in Asia from the late Miocene until the middle Pleistocene
• Largest primate that ever lived– perhaps as large as
300kg-
Chimpanzee skeleton
1. Hindlimbs shorter than forelimbs 2. Long pelvis 3. Knuckle walking 4. Protruding face 5. Spinal cord and the vertebrae enter into the cranium posteriorly
Paleoanthropology
study of human origins
Study of fossils of primates – especially Hominoidea
• AND traits themselves differ in timing and rates of evolution
Ardipithecus group: Sahelanthropus
tchadensis
Chad • Thicker enamel • Reduced prognathism • Massive brow ridge • Foramen magnum under the skull – suggests bipedalism • Brain 320-380 cc
Ardipithecus group: Orrorin tugenensis
Kenya • Like chimps in some ways, humans in other ways • Chimp-like front teeth – slight diastema • Human-like molars – smaller – with thick enamel • Maybe bipedal
Ardipithecus group: Ardipithecus ramidus
Ethiopia • Discovered 1992 • Females 120 cm; 50kg • Limb proportions similar to quadrupedal Miocene apes • Rigid-like foot (derived?) • Grasping toe (ancestral) • Woodland dwelling • Male and female canines similar size
Australopithecus Group
Erect • Bipedal • Relatively long forelimb (ape-like) • Sexually dimorphic (chimp-like) • Small brains (chimp-like) • Intermediate teeth – slight diastema – reduced canine – thicker enamel than ape
Locomotory transition: arboreal suspensory to
bipedal
- Postural adaptation for feeding
- Thermoregulatory (reduce surface area for insolation)
- Energetics of movement over open ground
- Carrying objects
Australopithecus
afarensis
Lucy • 40% complete skeleton • Adult female • 105-150 cm; 29-42 kg • Sex dimorphic • Skull/dentition – small braincase – prognathism – reduced canine – little bit of a diastema • Pelvis broad & narrow • Femoral neck long • Femur slants inward → Early bipedal • Arms somewhat longer relative to legs than in humans → Probably slept & foraged in trees
Australopithecus africanus
First identified in 1924 • ‘Taung Child’ • S Africa • ‘Southern ape of Africa’ • Small brain case • Face slightly protruding below the nose • Teeth large but proportions more similar to modern humans • Reduced canines
Australopithecus sediba
2008
• South Africa
• Small brain
• Good biped
Paranthropus
S & E Africa • Bipedal • Small brains • Robust masticatory apparatus but not entire body • Small incisors • Reduced canines • Massive cheek teeth • Large masticatory muscle – as per bony attachment on sagittal crest and mandible
Earliest Homo: H. habilis and
H. rudolfensis (2.8 - 1.5 mya)
• East Africa • Forelimb proportions similar to A. afarensis • Hand bones more robust than later Homo • Slightly enlarged brain (wide variation & body size larger too) • Sexually dimorphic (males > females • Reduced facial size and smaller teeth
what is the difference between human madibles and chimps mandibles
humans: parabolic
chimp: parallel
The Plio-Pleistocene
• Rapidly cooling climate
– ice sheets & land bridges; more of ocean ways are in ice sheets
– changes in vegetation
• Cooling selects for increased body size
• Environment of evolution of Homo ergaster and H. erectus
• Reduction in hominin diversity
Erectine distribution
Out of Africa events • Different selection pressures → Asian differentiation = erectus (dead end)
what is the nature of science
Science is guided by natural law
– Science has to be explained by reference to natural law
– Science is testable
– The conclusions of science are tentative
– Science is falsifiable
what is scientific method
Hypothetico-deductive Method:
Scientific process of making a conjecture (hypothesis)
based on observations and then seeking empirical tests
that potentially lead to its rejection
what is used for evidence of evolution
- fossil record
- stratigraphy
stratigraphy
Fossils in deeper rock are older than those above, and their position within these rock layers gives them a chronological age relative to older (deeper) or younger (surface) fossils.
fossil record
If species were created independently there would be no order to the fossil record. The fossil record is a dated sequence of morphological change
what does the fossil record do
- evidence for common ancestry
- evoluntary trends
- evidence of intermediate forms
- evidence of evoluntary stability
- evidence for evoluntary failure
Denisovans
Very limited fossils
– 1 finger bone
– 2 teeth
• DNA study
• Split from humans ~ 800 kya
• Dated to 100 kya
• Genetically related to H. neanderthalensis
• Some human populations have a few ‘Denisovan’ genes
– intermating of Denisovan (males) with ancestral ‘human’ females
H. neanderthalensis
• H. sapiens and H. neantherthalensis are sister species (derived from a common ancestor)
• Evidence for admixture varies
– at best early and little
• H. sapiens displaced H. neanderthalensis
Obstetrical Dilemma
• Human pelvis bowl-shaped
– adapted for bipedality
– but restricts size of birthcanal
• BUT giving birth requires a birth canal wide enough to
allow baby’s head through
• Dramatic increase in brain size after becoming bipedal
created a problem → obstetrical dilemma
maternal adaptations
• Increase in neonatal cranium → selective pressure on
– size of opening of female pelvis resulting in sexual dimorphism of the human pelvis
– softening of pubic symphyses at end of pregnancy
neonate adaptations
Bones of cranium not fused
– able to slip → allow compression during birth
– space for rapid post-natal brain development
