Hominid Evolution
Outline
•Background
•What is a hominid?
•Who are the hominids?
•Mosaic evolution
•Biocultural evolution
•Lumper vs. Splitter
•Conclusions
Background
Primate group
Hard to define vs. other mammalian orders
Trends in evolution include:
Skeleton/mode of locomotion
Increase in brain size
Smaller, fewer, less specialized teeth
Stereoscopic vision
Grasping hand, w/opposable thumb
Two suborders:
Prosimians
Anthropoids
–includes members of family Hominidae (aka hominids)
»Homoninae (humans and their extinct ancestors; aka
hominins)
»Gorillini (gorillas)
»Panini (chimps)
Climate
Miocene (23.03-5.33 mya) =Africa
Early to middle Miocene: warm climate
Late Miocene: cooler, drier
Pliocene (5.33-2.6 mya)=Africa
Climate cooler, more varied
Diversity of habitats
closed forest to open terrain
~ 2.5 mya major cooling event & global climatic change
Pleistocene=2.6 ma – 11,700
Marked by glacial, interglacial periods
ice sheets advanced, retreated
great environmental variation
Most of human evolution occurs
climatic change = important
Giant mammals abundant
ground sloth
mammoths
Mastodons
saber-toothed cat
What is a Hominoid?
Bipedalism--single diagnostic trait to identify hominid
Strong selective advantages
Bioenergetics/thermoregulation model
Endurance
Food resources
Line diverged from Old World monkeys before Miocene
Pre-Australopithecines
Sahelanthropus tchadensis
7-6 ma
Chad, Central Africa
Skull like apes’
Massive brow ridges
Small canine teeth
Lived in forest setting
Orrorin tugenensis “original man”
6 ma
Tugen Hills,Kenya, East Africa
Chimpanzee-looking teeth
Femurs indicate likely bipedalism
Forelimb similar to A. afarensis and apes
Lived in forest setting
Ardipithecus ramidus
4.4 ma
Aramis, Ethiopia, East Africa
Femur, pelvis indicate bipedalism
Most apelike
Lived in wooded setting
Genus Australopithecus
Gracile features of skull
Smaller body size
Long arms relative to legs
Long fingers/toes
Australopithecus afarensis
3.7-3 ma
East Africa
A woodland setting
Arboreal behavior patterns
Postcranially:
Long arms relative to legs
Long fingers/toes
“Lucy”= 3.2 ma, Hadar, Ethiopia
Laetoli footprints
3.7-3.5 ma
Laetoli, Tanzania
Fossil footprints attributed to A. afarensis
Robust Australopithecines (aka Paranthropus )
Robust features of skull = “chewing machines”
Smaller body size
Long arms relative to legs
Long fingers/toes
Robust Australopithecines (aka Paranthropus )
Australopithecus boisei
1.8 ma
Olduvai Gorge, Tanzania
Australopithecus africanus
3-2.3 ma
Kimberley, South Africa
Australopithecus robustus
~ 2-1 ma
Swartkrans, South Africa
Genus Homo
Increase in brain size, body size
Reduction in dentition
Development of technology
more efficient foraging/scavenging & hunting
Homo habilis
2.5-1.6 ma
Olduvai Gorge, Tanzania
Kenya
Homo erectus
500,000-230,000 years ago
Zhoukoudian, China
Peking Man
Homo ergaster=Turkana boy
Boy about 12 years of age
Height about 5ft. 3in.
(African Homo erectus)
1.6 ma
West Turkana, Kenya
Neanderthals
50,000-60,000 year ago
La Chapelle-aux-Saints, France Cro Magnon
Classic Neanderthal:
short
very robust
heavily built, especially in facial area
adapted to live in colder, harsher climates
Cro Magnon
30,000 years ago
Morphologically like modern humans
Les Eyzies, France
Mosaic evolution
Rate of evolution in one functional system varies from those of other systems
Physiological and behavioral systems evolve at different rates
In hominid evolution dentition, locomotion, brain size and tool making have
developed at different rates
Biocultural evolution-culture/developing culture=possible
Environmental challenges =human physical, cultural adaptations
Physical adaptations
Habitual bipedalism
Reduction in size of dentition
Enlargement of brain
Cultural adaptations
Development of technology
Tool industries
Simple to complex
Lumper vs. Splitter
Different interpretations of variation exhibited by hominid fossils
•Lumper: intraspecific variation
•(one taxonomic category)
•Splitter: interspecific variation
•(two or more taxonomic categories)
Ex. Genus Homo
Why such confusion...?
Resolution=not main issue
Form of conflicting views instructive.
Include all early Homo fossil remains from Africa within one species
considerable variation =largely to be due to sexual dimorphism- intraspecific
variation
Too much variation among specimens to be explained as part of one species
argue more than one species of early Homo- interspecific variation