Hominid Evolution

Chapter 19 Hominid Evolution

Kingdom Animal Phylum Chordate Class Mammal Order Primates Family Hominids Genus Homo Species Sapiens Classification Hierarchy (Linnaeus) Humans and apes diverged ~8 Mya

Diverged ~8 million years ago >12 different forms of hominids since then Humans and Apes

Oldest Hominid • Sahelanthropus tchadensis, • the oldest known hominid • 7 million years old • discovered in 2002 in Chad

Sahelanthropus tchadensis • Skull found in the African nation of Chad in 2002 • pushed back the origins of humans to nearly 7 million years ago • its discovery has raised more questions than it answered

“Bushy” Model of Human Evolution • Paleoanthropologists now think • human evolution branched many times • rather than evolving in a somewhat straight line • Key traits such as • upright walking • manual dexterity • “large” brain • evolved more than once, and produced many evolutionary dead-ends

Fossil hominids http://www.nature.com/nature/journal/v418/n6894/fig_tab/418133a_F2.html

Oldest Hominid • Sahelanthropus tchadensis shows a mosaic of primitive and advanced features • The small brain case and most of the teeth are chimplike • Fairly flat nose and the prominent brow ridges • are features only seen, until now, in the human genus Homo • Looks more human than hominids that came millions of years later!

Early History of Ancestral Hominids • Much of our knowledge • comes from fossils found in a small desert area southwest of Cairo, Egypt • During the Late Eocene and Oligocene • this region was a lush, tropical rain forest • supported a diverse and abundant fauna and flora

Thousands of Fossil Specimens • Several thousand fossil specimens • representing more than 20 species of primates • recovered from rocks of this region • One of the earliest ancestral hominids • was Aegyptopithecus, • small, fruit-eating, arboreal primate • weighed about 5 kg

One of the Earliest Ancestral Hominids • Skull of Aegyptopithecus zeuxis, • one of the earliest known anthropoids • ~30 Ma

Hominids • The hominids (family Hominidae) • primate family that includes present-day humans • fossil record extending back 7 million years • Hominids are bipedal • that is, they have an upright posture • Skeletal structure shows bipedal traits • Hominid brain organization: larger compared to other primates

Comparison of Locomotion • Comparison between quadrupedal and bipedal locomotion • in gorillas and humans • In gorillas the ischium bone is long • and the entire pelvis is tilted toward the horizontal

Comparison of Locomotion • In humans the ischium bone is much shorter • and the pelvis is vertical • Comparison between quadrupedal and bipedal locomotion • in gorillas and humans

Hominids: Larger Reorganized Brain • In addition, hominids show a trend • toward a large and internally reorganized brain • A large brain size and organization • is apparent in the brain of a present-day human

Response to Climatic Changes • Many anthropologists think • hominid features evolved in response to major climatic changes • During this time • vast savannas replaced the African tropical rain forests • where the lower primates had been so abundant

Mixed Forests and Grasslands • As the savannas and grasslands continued to expand • hominids made the transition from true forest dwelling • to life in an environment of mixed forests and grasslands

Geologic Age Ranges

Oldest Known Hominid • Discovered in Chad in 2002 • nearly 7-million-year-old skull and dental remains of Sahelanthropus tchadensis • make it the oldest known hominid yet unearthed

Australopithecus • Australopithecines are early hominids • genus Australopithecus • Currently, five species are recognized: • A. anamensis • A. afarensis • A. africanus • A. robustus • A. boisei

Evolutionary Scheme • Many paleontologists accept that • A. anamensis • the oldest known australopithecine, • is ancestral to A. afarensis, • who in turn is ancestral to A. africanus • and the genus Homo, • as well as the side branch of australopithecines • represented by A. robustus and A. boisei

Lucy • Knees worked like modern human knees • Makes 40% bigger than females • Males had large crests on the tops of their skulls • A reconstruction of Lucy’s skeleton • Lucy is a ~ 3.5-million-year-old • Australopithecusafarensis

Hominid Footprints • Preserved in volcanic ash in Tanzania • Discovered in 1978 • Proved hominids were bipedal walkers at least 3.5 million years ago

Hominid Footprints • Most scientists think the footprints • were made by Australopithecus afarensis • whose fossils are found nearby

Brain Size of A. afarensis • A. afarensis had a brain size of 380–450 cubic centimeters (cc), • larger than the 300–400 cc of a chimpanzee • much smaller than that of present-day humans (1350 cc average)

Apelike Features • The skull of A. afarensis retained many apelike features • massive brow ridges • forward-jutting jaw • teeth were intermediate between those of apes and humans • The heavily enameled molars • adaptation to chewing fruits, seeds, and roots

Landscape with A. afarensis • Re-creation of a Pliocene landscape • showing members of • Australo-pithecus afarensis • gathering and eating • various fruits and seeds

Skull of A. africanus • A reconstruction of the skull • of Australopithecus africanus • This skull, • known as that of the Taung Child, • was discovered by Raymond Dart in South Africa in 1924 • and marks the beginning of modern paleoanthropology

Not As Well Adapted for Bipedalism • It appears the limbs • of A. africanus may not have been as well adapted for bipedalism as those of A. afarensis

The Human Lineage: handy man Homo habilis • The earliest member of our own genus Homo • lived 2.5-1.6 million years ago • H. habilis evolved from the A. afarensis and A. africanus lineage • coexisted with A. africanus for about 200,000 years

Geologic Age Ranges • The geologic age ranges • for the commonly accepted species of hominids

Characteristics of Homo habilis • H. habilis had a larger brain (700 cc average) • than its australopithecine ancestors but smaller teeth • It was about 1.2-1.3 m tall and weighed 32-37 kg

Homo Erectus • In contrast to the australopithecines and H. habilis, • which are unknown outside Africa, • Homo erectus was a widely distributed species • migrated from Africa during the Pleistocene • Specimens have been found • not only in Africa • also in Europe, India, China ("Peking Man"), and Indonesia ("Java Man")

Survived in Asia Until About 100,000 Years Ago • H. erectus evolved in Africa 1.8 million years ago • and by 1 million years ago • was present in southeastern and eastern Asia, • where it survived until about 100,000 years ago

H. erectus Differed From Modern Humans • Although H. erectus developed regional variations in form, • the species differed from modern humans in several ways • Its brain size of 800-1300 cc, • though much larger than that of H. habilis, • was still less than the average for Homo sapiens (1350 cc)

Size Similar to Humans • H. erectus's skull was thick-walled • face was massive • prominent brow ridges • teeth were slightly larger than those of present-day humans • H. erectus was comparable to size to modern humans • between 1.6 and 1.8 m tall • weighing between 53 and 63 kg

Skull of Homo erectus • A reconstruction of the skull of Homo erectus • a widely distributed species • whose remains have been found in Africa, Europe, India, China, and Indonesia

H. erectus Was a Tool Maker • The archaeological record indicates • that H. erectus was a tool maker • Furthermore, some sites show evidence • that its members used fire and lived in caves • an advantage for those living in more northerly climates

Homo erectus Using Tools • Re-creation of a Pleistocene setting in Europe • in which members of Homo erectus are • using fire and stone tools

The "Out of Africa" View • Currently, a heated debate surrounds the transition • from H. erectus to our own species Homo sapiens • “Out of Africa" view • early modern humans evolved from a small African colony • offspring then migrated from Africa and populated Europe and Asia, driving the earlier hominid populations to extinction

The "Multiregional" View • “Multiregional" view • early modern humans did not have an isolated origin in Africa • established separate populations throughout Eurasia • Occasional contact and interbreeding • enabled our species to maintain its overall cohesiveness • still preserving the regional differences in people we see today

Homo sapiens Evolved From H. erectus • Regardless of which theory turns out to be correct, • our species, H. sapiens, most certainly evolved from H. erectus

Neanderthals • Neanderthals • inhabited Europe and the Near East • 200,000 to 30,000 years ago • Some paleoanthropologists : • as a Neanderthals are a subspecies of our own species (Homo sapiens neanderthalensis) • Others: separate species (Homo neanderthalensis)

Neanderthals Difference • Main difference between Neanderthals and present-day humans is in the skull • Neanderthal skulls were long and low • heavy brow ridges, a projecting mouth, and a weak, receding chin • Their brain was slightly larger on average • than our own, and somewhat differently shaped

Neanderthal Skull • Reconstructed Neanderthal skull • The Neanderthals were characterized • by prominent heavy brow ridges and weak chin

First Humans in Cold Climates • Given the specimens from more than 100 sites • we now know Neanderthals were not much different from us, only more robust • Europe's Neanderthals were the first humans • to move into truly cold climates • enduring miserably long winters and short summers • as they pushed north into tundra ecosystems

Burial Ceremony in a Cave • Archaeological evidence indicates • Neanderthals lived in caves • and participated in ritual burials • as depicted in this painting of a burial ceremony • such as occurred approximately 60,000 years ago • at Shanidar Cave, Iraq

Cro-Magnons • About 30,000 years ago • humans closely resembling modern Europeans • moved into the region inhabited by the Neanderthals and completely replaced them • Cro-Magnons • successors of the Neanderthals in France • 35,000 to 10,000 years ago • huge advances in development of art and technology

Cave Painters • Cro-Magnons were cave painters • Using paints made from manganese and iron oxides • painted hundreds of scenes on the ceilings and walls of caves in France and Spain • many of them are still preserved today

Painting From a Cave in France • Cro-Magnons were very skilled cave painters • Painting of a horse • from the cave of Niaux, France

Hominid Evolution