Exploring the Pleistocene Epoch and Human Evolution

2. The Great Ice Age • Pleistocene epoch (Ice Ages or Age of Humanity) - began about 1.6 million years ago (mya). • The major climate and environmental changes that took place during the Pleistocene were the backdrop for some of the most important stages in human evolution. • The Pleistocene epoch had constant fluctuations between warm and intensely cold global climates.

3. The Great Ice Age • Pleistocene epoch • The northern parts of Europe and North America were mantled with great ice sheets, the last retreating only some 15,000 years ago. • There have been at least nine of these glacial periods during the last 780,000 years, which is why the Pleistocene is sometimes called the Great Ice Age. • Interglacials, with climates as warm as or warmer than that of today, were rare, and the constant changes repeatedly displaced plants and animals from their original habitats.

4. The Origins of the Human Line • Aegyptopithecus - Oligocene, some 35 million to 30 million years ago - Aegyptopithecus zeuxis, Nile Valley. • Miocene Primates • dental apes - hominoids with apelike teeth but with monkeylike bodies (~23 mya). • Proconsul • Morotopithecus bishopi • Kenyapithecus • Nakalipithecus nakayamai

5. The Origins of the Human Line • Bipedalism - Early hominins became bipedal over a long period of time, perhaps as a result of spending more and more time feeding on food resources on the ground. • Bipedalism is a way of moving that is configured for endurance rather than power or speed. • Walking is highly effective for wide-ranging foraging or running a marathon.

6. Molecular Biology and HumanEvolution • Vincent Sarich and Alan Wilson - Developed a means of dating primate evolution. • Sarich and Wilson showed that the albumins of apes and humans are more similar than those of monkeys and humans. • They argued, apes and humans have a more recent common ancestry. • Estimated that chimpanzees and humans last shared a common ancestor about 5 million to 6 million years ago.

7. Molecular Biology and HumanEvolution • Results of the molecular clock using changes in beta globulin genes (Goodman) • split between monkeys and apes ~ 25 mya • split between the greater and lesser apes to about 17 mya • Gorillas split from the chimpanzee-human branch about 8 million years ago • the human line and chimpanzees about 7 to 8 million years before present

8. The Ecological Problems Faced by Early Hominins • Early hominin populations underwent adaptive changes through natural selection to solve environmental problems caused by the broader ecological community. • Adaptive problems • Being large mammals   • carrying capacity • Being terrestrial primates  • Living in a savanna environment  

9. Fossil Evidence: 7 to 4.0 mya • Summary of Fossil Hominins • Toumaï: Sahelanthropus tchadensis - between 6 million and 7 million years old. • Confirms what many people have long believed. Hominin evolution was much more complicated than was suspected a generation ago. • Ardipithecus ramidus - found in a 4.4-million-year-old layer at Aramis in the arid Awash region of Ethiopia.

10. The First Australopithecines: c. 4 to 3 mya • Australopithecus anamensis • Complete upper and lower hominin jaws, some teeth, and limb fragments of almost 80 individuals from Allia Bay and Kanapoi on Lake Turkana, Kenya. • These fossil finds date to about 4.2 to 3.9 mya.

11. The First Australopithecines: c. 4 to 3 mya • Australopithecus afarensis • Best known from the Hadar region of Ethiopia and from the Laetoli site in Tanzania (named “Lucy”). • Lucy was only 1.0 to 1.2 m (3.5 to 4.0 feet) tall and 19 to 21 years old. • The remains of at least 13 males, females, and children were also found. • Lucy herself has recently been dated to 3.18 mya by means of a variant of potassium- argon dating that uses computerized argon laser fusion.

12. The First Australopithecines: c. 4 to 3 mya • Laetoli: Footprints of A. afarensis • Dramatic confirmation of A. afarensis • excavated by Mary Leakey • potassium-argon-dated to 3.75 to 3.59 mya • The footprints came from the buried bed of a seasonal river, where thin layers of fine volcanic ash once formed a pathway for animals traveling to water holes.

13. Fossil Evidence: 3 to 2.5 mya • Gracile Australopithecines: Australopithecus africanus • Australopithecus africanus was a gracile, highly mobile hominin, marked in fossil form by small, almost delicate skulls and prognathous faces. • Found only in South Africa, africanus is an evolutionary mystery, for no one has yet found this form in East Africa, where A. afarensis flourished.

14. Fossil Evidence: 3 to 2.5 mya • Robust Australopithecines: A. aethiopicus, A. boisei, and A. robustus: • Found in both eastern and southern Africa • had small brains and large teeth that were specialized for chewing coarse, fibrous plant foods • Three species - A. aethiopicus, A. boisei, and A. robustus

15. Fossil Evidence: 3 to 2.5 mya • Australopithecus garhi: • stood about 1.46 m (4 feet 10 inches) tall • had protruding features, not unlike those of a chimpanzee • The lower molars are three times the size of those of modern humans, the canines almost as large. • Australopithecus garhi’s brain was only a third the size of that of a modern human. • The legs are long and humanlike, while the arms are long and more like an ape’s.

16. Early Homo: 2.5 to 2.0 mya • Sometime around 2 million to 1.8 million years ago, early forms of the genus Homo appeared, marked by larger brains, generally smaller jaws and teeth, and other features that seem to foreshadow modern human crania. • Homo habilis • Louis and Mary Leakey - Olduvai Gorge in 1960 • Richard Leakey - the famous Skull 1470 in East Turkana, a large-brained, round-headed cranium that confirmed the existence of H. habilis in no uncertain terms

17. Early Homo: 2.5 to 2.0 mya • Homo habilis (cont.) • about 1.3 m (4 feet 3 inches) tall and about 40 kg (88 pounds) • H. habilis would have looked less apelike than Australopithecus, around the face and skull. • The head was higher and rounder, the face less protruding, the jaw smaller.

18. Who Was the First Human? • In recent years, four criteria have been generally used to assign a fossil to the genus Homo: • an absolute brain size of 600 cc • the possession of language • the possession of a modern, humanlike precision grip and an opposable thumb • the ability to manufacture stone tools • This definition of Homo makes a clear distinction between the hominins of earlier than 1.9 million years ago and Homo erectus and its successors who evolved after that date.

19. Archaeological Evidence for Early Human Behavior • Four lines of evidence offer opportunities for testing hypotheses about early hominin behavior: • 1. Scatters of artifacts • 2. Manufactured artifacts • 3. Surviving food remains • 4. Isotopic analyses

20. Archaeological Evidence for Early Human Behavior • Evidence for “Central Places”? • All archaeology currently tells us is that the early Olduvai sites were places to which stone and food resources were carried. • These may have been the remote predecessors of hunter-gatherer central places, which were to come into being in later times, conceivably with the regular use of fire for heat and protection.

21. Archaeological Evidence for Early Human Behavior • Hunting and Scavenging • Were these hominins full-fledged hunter-gatherers, or did they scavenge predator kills for meat? Or both? • taphonomy • microwear studies • diverse carnivore and ungulate communities

22. Plant Foraging and “Grandmothering” • A scanning electron microscope focused on tooth microwear has shown that some Lower Pleistocene hominins had diets very similar to those of modern nonhuman primates. • Grandmother Hypothesis (O’Connell) - Very often, women in their 60s and 70s are more efficient foragers than their younger female kin of reproductive age. • By the age of 5, children can supply as much as half their daily nutritional requirements by their own efforts. • Both mothers and grandmothers deliberately target easy-to-acquire foods such as fruit during the rainy season, which children can also take in large numbers.

23. Toolmaking • Human beings manufacture tools regularly and habitually and with much more complexity than do Chimpanzees. • The Oldowan Industry – Chipped stone tool industry found in Africa dating from 1.8 mya. • Mary Leakey • Nicholas Toth • Julio Mercader

24. The Mind of the Earliest Humans • Homo habilis shared the ability of their earlier ancestors to “map” resources over the landscape, their intelligence amplified by toolmaking. • Nicholas Toth • Leslie Aiello and Peter Wheeler • Steven Mithen

25. The Development of Language • Despite the enhanced skill of communicating with others, the first humans probably had only the most rudimentary forms of speech, in addition to the grunts and gestures of other primates.

26. Social Organization • Homo habilis may have lived in larger groups, something made possible by greater social intelligence resulting from larger brain size.