Chapter Study Outline

  1. First Hominins
    1. Six million years ago, climate and geographic change led to the evolution of hominins.
    2. Characteristics of humans include:
      1. Bipedalism
      2. Differences in dental anatomy from apes
      3. Large brains relative to body size
      4. Long period of juvenile development
      5. Dependence on a material and symbolic culture
    3. Hominins shared some of the features of humans and also some features of contemporary chimpanzees.
  2. Chimp-Human Split
    1. Between 7 to 5 mya, the common ancestor of chimps and humans roamed the earth.
    2. Sahelanthropus tchadensis, discovered in 2002, is the earliest known hominin, living around 7 to 6 mya. It has both derived and primitive features.
    3. Orrorin tugenensis, discovered in 2001, is also similar to both chimps (e.g., teeth) and humans (e.g., leg bones).
    4. Ardipithecus includes two species, ramidus and kadabba, that each have similarities to chimps and humans.
  3. Diverse Hominins
    1. Australopithecus
      1. Au. anamensis, an early hominin dated from 4.2 to 3.8 mya, was bipedal, but its skull was more apelike. Large molars, small canines, and arm bones mark it as hominin, while the chin and dental arcade have more primitive features.
      2. Au. afarensis dates from about 4 to 3 mya and includes Lucy, a well-known female specimen. The human-looking knee and hip joints clearly indicated a bipedal individual; the skull and dentition, however, were apelike. The Laetoli footprints confirm bipedal locomotion, but this species likely spent time in trees as well.
      3. Au. africanus, which dates from 3 to 2.2 mya, was identified in the first part of the twentieth century and includes the Taung child's skull. Postcranial anatomy and the position of the foramen magnum indicate this species was bipedal. It additionally has more derived traits than afarensis, including dental differences associated with chewing and quick juvenile maturation, as found in chimpanzees.
      4. Au. garhi lived around 2.5 mya and was found in 1999. Although it was similar in brain size to other australopithecines, the teeth were much larger, and garhi had a sagittal crest to anchor large chewing muscles.
    2. Paranthropus
      1. P. aethiopicus from around 2.5mya has specialized anatomy for heavy chewing.
      2. P. robustus, another robust hominin, dates from 1.8 to 1 mya, and is even more specialized for heavy chewing than aethiopicus.
      3. P. boisei is larger still than the other two paranthropids, with a body type sometimes called hyperrobust, and dates from 2.2 to 1.3 mya.
    3. Kenyanthropus
      1. K. platyops is a relatively new fossil find that is different from the australopithecines and the paranthropids, with features not found in any other genus.
    4. Homo
      1. The earliest species of Homo appeared from about 1.9 to 1.6 mya.
      2. Although there has been controversy over whether habilis and rudolfensis are members of the genus Homo or Australopithecus, the size of the brain led the Leakeys to classify them with Homo.
      3. While H. habilis is more gracile, H. rudolfensis is more robust.
  4. Phylogenies
    1. Various phylogenies of how humans evolved can be constructed.
    2. Discoveries of new species and new specimens can change phylogenetic relationships.
  5. Advent of Bipedalism in Early Hominin Morphology and Behavior
    1. Theories of bipedalism
    2. Walking is efficient locomotion on the ground.
    3. Our ancestors were suspensory feeders.
    4. Moving on two legs keeps a hominin cooler.
      1. Walking on two legs leaves the arms free to carry objects.
      2. It's easier to gather fruit from small trees on two legs with free arms.
    5. Subsistence
      1. Hominins developed strategies for dealing with lack of food in the dry season.
      2. Early hominins may have hunted for meat.
      3. Hominins may have used tools like modern chimps do.
      4. Social organization
      5. Food sharing may have been important to early hominins.
      6. Early hominins may have lived in multimale, multifemale groups.
      7. It's possible that early male hominins invested little in their offspring.