human evolution Flashcards
lecture 14 - Mark Briffa
human phylogeny - part one
vertebrates : chordates with a backbone
gnathostomes : vertebrates with jaws
tetrapods : gnathostomes with limbs and feet
amniotes : tetrapods with eggs adapted for land
mammals : amniotes with hair and that lactate ( class - mammalia )
human phylogeny - part two
Eutherians : placental mammals
primates : eutherians with hands and feet adapted for grasping. no claws, large brain, short jaws, stereo vision. (order)
anthropoids : primates with a somewhat opposable thumb
hominoids : anthropoids with a fully opposable thumb - apes and humans
hominins
hominoids more closely related to modern humans than modern chimps, gorillas or orangutans
forehead : differences between modern Hominins and Panins
human: steep forehead, flat face
chimpanzee: low forehead, projecting face
brain : differences between modern Hominins and Panins
human: large brain (14 - 1600 cc), large cranial size at birth
chimpanzee: small brain (400cc)
teeth : differences between modern Hominins and Panins
human: small canines, large molars
chimpanzee: large canines, small molars
bipedal : differences between modern Hominins and Panins
bipedal - using 2 legs for walking
human: fully bipedal - foramen magnum under skull
chimpanzee: partially bipedal - foramen magnum at back of skull
earliest hominins
three candidate groups of fossils:
- Sahelanthropus tchadensis
- Orrorin tugensis
- Ardipithecus ramidus
very limited material
fossils from 6-4.5 mya
Australopithecus
archaic hominins from east Africa
(earliest hominin. - unknown if related to humans)
- several species
- A. afarensis discovered in 1974, Ethiopia
- 4.5 - 4 mya
- 1m tall
- fully bipedal
- but small brained relative to modern humans 400-500 cc
bipedal locomotion
- key adaptation in hominids
- anthropoid ancestors were arboreal ( living in trees ) - (30 - 35 mya)
- didnt evolve in one go
- long distance bi-pedalism only evolved 1.9 mya
- a pre-adaptation for other hominid features
savannah theory : bipedal locomotion
a hypothesis that human bipedalism evolved evolved as a direct result of human ancestors transition from an arboreal lifestyle to one on the savannas
*widely excepted
aquatic ape theory - bipedal locomotion
our ancestors once spent a significant part of their life in water
- not really accepted
functional morphology of A. afarensis
- brain bigger than chimp but so is body
- small incisors and big molars suggests diet of tough food (prob. plant based)
- capable of bi-pedal walking but only over short distances
- large zygomatic arches : massive jaw muscles
- rectangular ( or U shaped ) arrangment of teeth
- protruding jaw
A. garhi
- east africa 2.5 mya
- even larger chewing teeth
- ‘megadont’ (having larger teeth)
- fossil animal bones with scrap-marks found in same site : first evidence of tool use and de-flehing animal carcases
dexterity
performing tasks with hands
manual dexterity in humans:
- power grip
- precision grip
( change to bipedalism allowed selection on hands )
australopiths
Paranthropus spp., a robust australopith 2.3 - 1.2 mya, Southern Africa
Australopithecus africanus, gracile australopith 3 - 2.5 mya, Southern Africa, bipedal but possibly arboreal
transitional hominins
earliest example of genus Homo
- Homo habilis
600-700 cc, ‘handy man’, 2.4 mya Olduvai gorge Tanzania, controversial: may be an australopith, possibility of spoken language based on false assumptions about brain morphology ( Broca’s area ) - H. rudolphensis
500-800 cc, bigger wider faltter face, 1.9 mya Lake Turkana Kenya, large chewing muscles, very little known about species
pre-modern homo
- homo ergaster
- 5 mya - kenya, slender, fully bipedal, low sexual dismorphism
- homo eructus
- 2 mya - kenya, ‘peking man’, may be the direct ancestor of modern humans, first ti migrate out of africa 1.5 mya
Homo neanderthalensis
- many similarities with modern humans
- upto 1900 cc
- evidence for interbreeding with early H. sapiens in europe
- but modern humans not directly descended from neaderthalensis (share some DNA)
- 0.2 mya - 0.04 mya
hominin average brain size
H. neanderthalensis : up to 1900cc
H. sapiens : average 1400cc
H. erectus : average 900cc
H. habilis : average 650cc
Homo sapiens : modern hominins
- oldest fossils 185-160,000 years old in Ethiopia - possibly split 365k years ago
- moden humans evolved in africa
- lack heavy brow ridges
- oldest fossils outside africa 100,000 years old
- oldest in new world 15,000 years ago
- the only extant hominin
out of Africa hypothesis : the spread of humans
a model for the origin and dispersal of modern humans. The hypothesis contends that humans evolved in East Africa, dispersing to populate the rest of the world from c. 70,000 years ago, replacing, rather than interbreeding with, the archaic hominins that were resident outside of Africa
hominin adaptations
hominins are hominoids with:
- full bipedalism
- dextrous hands
- smaller jaws and teeth
- very large brains
- reduced sexual dismorphism
- unique social and cultural behaviour
