Anthropology Questions 2

Lecture #16 — The Australopithecines and Early Homo The Big Questions • What are the characteristics of the australopithecines? • How can understanding anatomy help us understand behavior? • When did our ancestors first use stone tools? Human Evolution Is Mosaic • Not all of the traits we associate with modern humans emerged at the same time. – The australopithecines are clearly bipedal but they have relatively small brains and pretty big molars with thick molar enamel. – Bigger brains appear with the first members of our own genus, Homo habilis , and then get a lot bigger with Homo erectus. – We will also see a general trend toward less skeletal and dental robusticity over time. The Australopithecines were… • A diverse group of Plio -Pleistocine African hominins – Pliocene 5.5 – 2.5mya – Pleistocene 2.5mya – 10,000ya • Divided into two genera (plural of genus) – Australopithecus or Gracile Australopithecines – Paranthropus or Robust Australopithecines http://humanorigins.si.edu/sites/default/files/imagecache/medium_banner_520px_height/images/banner/2.3.2 -7_wo_bars.jpg Hominin Sites Genus Australopithecus Gracile Australopithecines • Australopithecus anamensis – 4.2 -3.9mya – Allia Bay and Kanapoi , Kenya • Australopithecus afarensis – 3.7 -3mya – Laetoli and Hadar , Ethiopia • Australopithecus africanus – 3 -2mya – South Africa Australopithecus afarensis will be our prototypical australopithecine. Australopithecus anamensis 4.2 - 3.9mya Australopithecus anamensis — 4.2 -3.9mya Allia Bay and Kanapoi , Kenya (near Lake Turkana) Australopithecus afarensis 3.7 - 3mya Australopithecus afarensis — 3.7 -3mya Ethiopia Lucy — Hadar , Ethiopia Australopithecus africanus 3 - 2mya Adult specimen from Sterkfontein Australopithecus afarensis Lucy — Hadar , Ethiopia 3.18mya Lucy — The Most Famous Fossil • Discovered in 1974 by Donald Johansen and Tom Gray • 40% complete skeleton • 3.5’ tall Laetoli Footprints, Tanzania 3.6mya Laetoli Footprints • Preserved in volcanic ash • 3.6mya • Bipedal — Legs lock into position when standing erect, inward angling femur, big toe not opposable, anterior foramen magnum • Height for females 3.5 – 4’; males as high as 5’. • Marked sex differences in the canines. – Sexual dimorphism comparable to baboons and gorillas  non -monogamy General Characteristics • Post -Cranial Skeleton – Small body size (3.5 -4.5’) – Arms and fingers relatively long • Suggests they were likely still spending time in trees — foraging? Sleeping? – Humerus not weight -bearing – Pelvis rounded – Tibia and femur bipedal Cranio - Facial Anatomy (Australopithecus afarensis ) Cranio - Facial Anatomy • Foramen Magnum – Anterior like modern humans • Cranial Capacity – Chimpanzees 350 -400 – Australopithecines 400 -500 – Humans (1200 -1600) • Forehead – Chimpanzees and Australopithecus lack a forehead (associated with growth in brain, particularly frontal lob) – Post -orbital constriction — pinching behind the eye orbits • Chimpanzee and Australopithecus show constriction, chimpanzee more pronounced • Supraorbital Torus ( browridge )— Chimpanzee>Australopithecus>human Cranio - Facial Region • Size of Facial Region – Zygomatic Arch (cheekbones) — masseter muscle attachments • Australopithecines have large zygomatic arches to support large masseter muscles; force focused on molars • Chimpanzees and humans have smaller zygomatics – Mid -facial prognathism — jutting out of the mid -face • Chimpanzees show more mid -facial prognathism than australopithecines; australopithecines more than humans •  Early hominins generally intermediate between chimps and humans but the major changes in the cranial anatomy occur later than the emergence of bipedalism Dentition (Pan troglodytes, Australopithecus afarensis , Homo sapiens) Dentition • Incisors and Canines – Chimpanzee and human incisors are more prominent than australopithecines  characteristic of fruit -eating primates – Chimp canines are sharper and more pronounced than australopithecine or human • female and male chimp canines larger but male chimp > female chimp • australopithecine canines are more on the human scale reflecting dietary and social adaptations – using nondental means to process foods and defend or compete  TOOLS and CULTURE! Dentition • Molars – Australopithecines have large molars and premolars — extended grinding surface on the molars for chewing • thick enamel on molars — grinding adaptation; many specimens show significant molar wear – Apes and humans have thin molar enamel — fruit -eating and food processing • Australopithecines have a U -shaped dental arcade, intermediate between parallel chimpanzee and parabolic human Mosaic Evolution • Australopithecines show some similarities to Pan spp., some to humans, some unique • Over time, chewing apparatus reduced, brain enlarged • Trend from Australopithecus to Homo is a marked increase in size of braincase relative to face and teeth • Paranthropus aethiopicus – 2.5mya – Black Skull, Lake Turkana, Kenya • Paranthropus robustus – 2 -1.3mya – South African fossils • Paranthropus boisei – 1.5mya, – Olduvai Gorge Paranthropus or Robust Australopithecines Characteristics • Dentition – Small front teeth – Enormous grinding molars – Mandible large and deep • Postcranial – Similar in size and features to Australopithecus • ATE GRASSES! Paranthropus aethiopicus — The Black Skull Sagittal crest supports muscle attachments for temporalis muscles — HUGE muscles for major molar grinding. Chewing the cud! Paranthropus boisei KNM - ER 406 Early Hominin Behavior • “Man -the -Hunter”? – Raymond Dart, and other early paleoanthropologists, argued that early hominins were pair -bonded species in which males hunted and provisioned females and offspring in exchange for monopolizing sexual access to a female • What does the evidence suggest? Early Hominin Behavior • “Man -the -Hunter” • “Hominid -the -Hunted -Omnivore” – Lots of australopithecine remains found in association with large predators – The little hominins show clear taphonomic signs of having been consumed by the larger predators • Leopards and really big eagles – both leave distinctive teeth/claw marks on prey (including little hominins ) Early Hominin Behavior • The Australopithecine Adaptation – Long distance travel to collect plant and animal foods (insects are animals) – Large grinding teeth  tough , gritty foods – Tools — social learning and transmission • Not stone tools yet but tools of perishable materials • What about food sharing and mating? – Let’s think comparatively, look at other primates with similar sexual dimorphism… Early Hominin Behavior Species Female Body Weight as % of Male Mating System Gibbons/ Siamangs (Hylobates spp.) 98 -100% Pair -bonded Orangutan ( Pongo pygmaeus ) 50% Polygynous Gorilla ( Gorilla gorilla ) 40 -50% Uni -Male Bonobos/Chimpanzees (Pan spp.) 82% Polygamous Australopithecus afarensis 64% ? A. africanus 73% ? A. robustus 80% ? A. boisei 69% ? Modern Humans ( Homo sapiens ) 83% ? Early Hominin Behavior • Dart suggested pair -bonding and males provisioning females. – Pair -bonded species, like gibbons and siamangs , show virtually no sexual dimorphism. – That does not appear to be the case with australopithecines. – The degree of sexual dimorphism they show is somewhere between polygynous and promiscuous species. – There is no reason to suspect that early hominins would deviate from this pattern. – What about modern humans? Hmmm… Early Hominin Behavior • What about food sharing? – Again, the comparative method is useful. – Male and female bonobos and chimpanzees hunt. In fact, in bonobos more females have been seen hunting than males. – Adult female chimpanzees share food with offspring and with unrelated females and their offspring, and occasionally share meat with males – Males almost never share food, with the exception of occasional meat sharing •  No evidence to suggest that food sharing in early hominins was primarily male -to -female What about Dart’s Hypothesis, Then? • Reflects the dominant early -to -mid 20 th century gender and economic constructions in the West more than the evidence and, in fact, is inconsistent with data from living human groups. – Of 400 surveyed human societies in 1967, 80% practiced some form of polygyny , 20% practiced some form of monogamy (mostly serial monogamy). Becoming Human Transitioning to Homo • Homo habilis – Louis Leakey at Olduvai Gorge • 2 -1.8mya – Stone Tools • Oldowan Tool Culture • 2.5mya • Early Homo – Many specimens of unclear species designation – Some authors prefer not to assign species designations, referring to all pre -Homo erectus Homo specimens as early Homo Australopithecus afarensis Homo habilis General Trends from Australopithecus to Homo • Comparing the skulls, can see a general decrease in robusticity and increase in the proportion of the cranium taken up by the brain case. Characteristics of Early Homo • Cranium – 500 -800cc – Less robust – Reduced prognathism • Dentition – Overall reduction in size – More omnivorous • Post -Cranial – Similar size to Australopithecus Homo habilis in the Environment • General drying trend BUT it is characterized by short -term climatic fluctuations between wetter and drier periods – This rapidly fluctuating environment is selecting for increasing brain size  BEHAVIORAL FLEXIBILITY (culture as the human adaptive strategy) • Omnivorous diet – Meat makes up an part of the diet but Early Homo is NOT doing any substantial hunting; we are still talking about scavenging, opportunistic hunting of small vertebrates and majority diet of plant foods Along edges of forest for roots and tubers Along stream banks: stone to use as tools Trees provide nuts and fruits Scavenging from carcasses left by carnivores Opportunistic hunting of small game Oldowan Tool Technology Oldowan Tools • Stone tools first appear in the fossil record associated with the emergence of Homo • Choppers, scrapers, flakes • Percussive technique • Shows significant cognitive leap, planning