Hominid Origins

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Chapter 8

• Hominid Origins

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Chapter Outline

• Early Primate Evolution
• Miocene Fossil Hominids
• Definition of Hominid
• The Bipedal Adaptation
• Biocultural Evolution The Human Capacity for
  Culture
• Paleoanthropology as a Multidisciplinary Science

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Chapter Outline

• Dating Methods
• Early Hominids from Africa
• Australopithecus from East Africa
• Early Homo
• South African Hominids
• Interpretations What Does It All Mean?

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Early Primate Evolution

• The roots of the primate order go back to the
  beginnings of the placental mammal radiation
  circa 65 m.y.a.
• The earliest primates were diverging from quite
  early primitive placental mammals.
• A vast number of fossil primates from the Eocene
  (5534 m.y.a.) have been discovered and now total
  more than 200 recognized species.

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Eocene Primates

• Fossil primates from the Eocene display
  distinctive primate features.
• Looking at the whole array of Eocene primates, it
  is certain that they were
• Primates
• Widely distributed
• Mostly extinct by the end of the Eocene.

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Early Eocene Primates Features

• Chinese fossils dating from the early Eocene
  (5545 m.y.a. have three interesting features
• Forward rotation of the eyes, a feature that
  makes them distinct from the lemur-loris lineage.
• The cranium shows small eye sockets, suggesting
  they may have been diurnal.
• They were all apparently extremely small,
  weighing less than 1 ounce.

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Oligocene Primates

• The Oligocene (3423 m.y.a.) yielded fossil
  remains of several species of early anthropoids.
• By the early Oligocene, continental drift had
  separated the New World from the Old World.
• It has been suggested that late in the Eocene or
  very early in the Oligocene, the first
  anthropoids arose in Africa and reached South
  America by rafting over the water separation on
  drifting chunks of vegetation.

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Major Events inEarly Primate Evolution
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Miocene Hominoid Distribution, From Fossils Thus
Far Discovered
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Miocene Fossil Hominoids

• African forms (2314 m.y.a.)
• Especially from western Kenya, these hominoids
  are, in many ways, primitive.
• European forms (1611 m.y.a.)
• From scattered localities in France, Spain,
  Italy, Greece, Austria, Germany, and Hungary,
  most are quite derived.

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Miocene Fossil Hominoids

• Asian forms (167 m.y.a.)
• The largest and most varied group from Turkey
  through India/Pakistan and east to southern
  China, most are highly derived.

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Miocene Hominoid Fossils

1. These are hominoidsmore closely related to the
   ape-human lineage than Old World monkeys.
2. Mostly large-bodied hominoids, more akin to the
   lineages of orangutans, gorillas, chimpanzees,
   and humans than smaller-bodied apes.
3. Most of the Miocene forms thus far discovered are
   so derived that they are probably not ancestral
   to any living form.

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Miocene Hominoid Fossils

1. One lineage that appears well established relates
   to Sivapithecus from Turkey and Pakistan. This
   form shows some derived facial features similar
   to the modern orangutan, suggesting a fairly
   close evolutionary link.
2. Evidence of definite hominids from the Miocene
   has not yet been indisputably confirmed. However,
   exciting new finds from Kenya, Ethiopia, and Chad
   (the latter dating as far back as 7 m.y.a.)
   suggest that hominids diverged sometime in the
   latter Miocene.

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Patterns of Evolution

• Mosaic evolution
• Evolutionary pattern in which physiological and
  behavioral systems evolve at different rates.
• Biocultural evolution
• Biology makes culture possible and developing
  culture further influences biological evolution.

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Mosaic Evolutionof Hominid Characteristics
Locomotion
Modern Homo sapiens Bipedal shortened pelvis body size larger legs longer fingers and toes not as long
Early hominid Bipedal shortened pelvis differences from later hominids, smaller body size and long arms relative to legs long fingers and toes probably capable of considerable climbing
Miocene, generalized hominoid Quadrupedal long pelvis some capable of considerable arm swinging, suspensory locomotion
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Mosaic Evolutionof Hominid Characteristics
Brain
Modern Homo sapiens Greatly increased brain sizehighly encephalized
Early hominid Larger than Miocene forms, moderately encephalized prior to 6 m.y.a., no more encephalized than chimpanzees
Miocene, generalized hominoid Small compared to hominids, but large compared to other primates a fair degree of encephalization
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Mosaic Evolutionof Hominid Characteristics
Dentition
Modern Homo sapiens Small incisors canines further reduced molar tooth enamel caps thick
Early hominid Moderately large incisors canines somewhat reduced molar tooth enamel caps very thick
Miocene, generalized hominoid Large front teeth (including canines) molar teeth variable, depending on species some have thin enamel caps, others thick enamel caps
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Mosaic Evolutionof Hominid Characteristics
Toolmaking Behavior
Modern Homo sapiens Stone tools found after 2.5 m.y.a. increasing trend of cultural dependency apparent in later hominids
Early hominid In earliest stages unknown no stone tool use prior to 2.5 m.y.a. more oriented toward tool manufacture and use than chimpanzees
Miocene, generalized hominoid Unknownno stone tools probably had capabilities similar to chimpanzees
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Revised Classificationof Hominoids
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The Bipedal Adaptation

• Efficient bipedalism as the primary form of
  locomotion is seen only in hominids.
• Advantages of bipedalism
• Freed the hands for carrying objects and for
  making and using tools.
• In the bipedal stance, animals have a wider view
  of the surrounding countryside.
• Bipedal walking is an efficient means of covering
  long distances.

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Obligate Bipedalism

• Bipedalism as the only form of hominid
  terrestrial locomotion.
• Since major anatomical changes in the spine,
  pelvis, and lower limb are required for bipedal
  locomotion, once hominids adapted this mode of
  locomotion, other forms of locomotion on the
  ground became impossible.

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Major Features of Hominid Bipedalism

• The foramen magnum (shown in red) is repositioned
  farther underneath the skull, so that the head is
  more or less balanced on the spine (and thus
  requires less robust neck muscles to hold the
  head upright).

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Major Features of Hominid Bipedalism

• The spine has two distinctive curvesa backward
  (thoracic) one and a forward (lumbar) onethat
  keep the trunk (and weight) centered above the
  pelvis.

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Major Features of Hominid Bipedalism

• The pelvis is shaped more in the form of a basin
  to support internal organs moreover, the ossa
  coxae are shorter and broader, thus stabilizing
  weight transmission.

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Major Features of Hominid Bipedalism

• Lower limbs are elongated, as shown by the
  proportional lengths of various body segments
  (e.g., in humans the thigh comprises 20 of body
  height, while in gorillas it comprises only 11).

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Major Features of Hominid Bipedalism

• The femur is angled inward, keeping the legs more
  directly under the body modified knee anatomy
  also permits full extension of this joint.

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Major Features of Hominid Bipedalism

• The big toe is enlarged and brought in line with
  the other toes in addition, a distinctive
  longitudinal arch forms, helping absorb shock and
  adding propulsive spring.

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Paleoanthropology

• Paleoanthropology is defined as the study of
  early humans.
• Paleoanthropologists reconstruct the anatomy,
  behavior, and ecology of our ancestors
• It is a diverse multidisciplinary pursuit seeking
  to reconstruct every bit of information possible
  concerning the dating, anatomy, behavior, and
  ecology of our hominid ancestors.

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Components of Paleoanthropology
Physical Sciences Biological Sciences Social Sciences
Geology Physical anthropology Archaeology
Geomorphology Ecology Ethnoarchaeology
Geophysics Primatology Cultural anthropology
Chemistry Psychology
Taphonomy
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Dating Methods

• Paleoanthropologists use two types of dating
  methods to tell us the age of sites and fossils
• Relative dating determines only whether an object
  is older or younger than other objects.
• Chronometric (absolute) dating provides an
  estimate of age in years based on radioactive
  decay.

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Relative and Chronometric Dating
Relative Dating Chronometric Dating
Examples Stratigraphy Fluorine Dating K/Ar Radiocarbon (14 C) Fission-track
Methodological basis Provides a sequence only i.e., no estimates in actual number of years Most techniques are radiometric i.e., steady decay of radioactive isotope provides estimate in actual number of years
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Relative Dating Techniques

• Stratigrapy - based on the law of superposition,
  that a lower stratum (layer) is older than a
  higher stratum.
• Fluorine analysis applies to buried bones and
  groundwater seepage. Bones incorporate fluorine
  during fossilization.

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Relative Dating Techniques

• Biostratigraphy - related to changes in the
  dentition of animals.
• Paleomagnetism - based on the shifting of the
  geomagnetic pole.

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Chronometric Dating Techniques

• The age of an object can be determined by
  measuring the rate of disintegration
• Potassium/argon (k/Ar) dating involves the decay
  of potassium into argon gas. K/Ar has a half-life
  of 1.25 billion years.
• Carbon-14 is a radiometric method commonly used
  by archeologists. Carbon 14 has a half-life of
  5730 years.

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Position of the Foramen Magnum

• (a) a human and (b) a chimpanzee.
• Note the more forward position in the human
  cranium.

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Key Very Early Fossil Hominid Discoveries
(pre-Australopithecus)
Site Dates(m.y.a.) Hominids
East Africa Middle Awash (Ethiopia five localities) 5.85.2 Ardipithecus
East Africa Aramis (Ethiopia) 4.4 Ardipithecus ramidus
Central Africa Tugen Hills 6.0 Orrorin tugenensis
Central Africa Toros-Menalla 7.0 Sahelanthropus tchadenis
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Features of Australopithecus

1. They are all clearly bipedal (although not
   necessarily identical to Homo in this regard).
2. They all have relatively small brains (i.e., at
   least compared to Homo).
3. They all have large teeth, particularly the back
   teeth, with thick to very thick enamel on the
   molars.

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Laetoli

• Dated at between 3.5 and 3.7 m.y.a.
• Fossilized hominid footprints were found in an
  ancient volcanic bed.
• Despite agreement that these individuals were
  bipedal, some researchers feel they were not
  bipedal in the same way as modern humans.

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Hadar (Afar Triangle)

• Dating suggests a range from 3.9 to 2.3 m.y.a.
• Recovered
• "Lucy" an Australopithecus afarensis female, was
  recovered here.
• Group of bones representing 13 individuals,
  including 4 infants, suggest a social unit died
  at the same time.
• Some stone tools may be 2.5 million years old,
  making them the oldest cultural evidence yet
  found.

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Koobi Fora (East Lake Turkana)

• This site yielded the richest assemblage of
  Plio-Pleistocene hominids from the African
  continent.
• Most of the hominids date to 1.8 m.y.a., others
  date back to 3.3 m.y.a.
• 150 hominid specimens recovered at Koobi Fora
  represent at least 100 individuals.

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West Turkana

• Two important discoveries
• Discovery of a nearly complete 1.6 m.y.a. Homo
  erectus adolescent.
• Discovery of the black skull, a well-preserved
  2.4 million year old skull which caused a major
  reevaluation of Plio-Pleistocene evolution.

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Olduvai Gorge

• Louis and Mary Leakey conducted continuous
  excavations from the 1930's to early 1980.
• Paleontological evidence includes more than 150
  species of extinct animals which can provide
  clues to the ecological conditions of early
  hominid habitats.

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South African Sites

• The first australopithecine the missing link
  between apes and humans was discovered at a
  quarry at Tuang.
• As the number of discoveries accumulated, it
  became clear that the australopithecines were not
  simply aberrant apes.
• The acceptance of the australopithecines as
  hominids required revision of human evolutionary
  theory.

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Estimated Body Weights and Stature in
Plio-Pleistocene Hominids
Body Weight Body Weight Stature Stature
Male Female Male Female
A. afarensis 99 lb 64 lb 59 in. 41 in.
A. africanus 90 lb 65 lb 54 in. 45 in.
South Africanrobust 88 lb 70 lb 52 in. 43 in.
East African robust 108 lb 75 lb 54 in. 49 in.
H. habilis 114 lb 70 lb 62 in. 49 in.
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Steps in Interpreting Homind Evolutionary Events

1. Selecting and surveying sites.
2. Excavating sites and recovering fossil hominids.
3. Designating individual finds with specimen
   numbers for clear reference.
4. Cleaning, preparing, studying, and describing
   fossils.

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Steps in Interpreting Homind Evolutionary Events

1. Comparing with other fossil materialin
   chronological framework if possible.
2. Comparing fossil variation with known ranges of
   variation in closely related groups of living
   primates and analyzing ancestral and derived
   characteristics.
3. Assigning taxonomic names to fossil material.

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Groups of Plio-Pleistocene Hominids

• Specimens represent 200 individuals from South
  Africa and more than 300 from East Africa.
• Divided into four broad groupings
• Set I Basal Hominids.
• Set II Early Primitive Australopithecus.
• Set III Later, more derived Australopithecus.
• Set IV Early homo.

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Set I. Basal Hominid(4.4 m.y.a.)

• The earliest and most primitive remains are those
  from Aramis.
• They have been classified as Ardipithecus
  ramidus, a different genus from all other
  Plio-Pleistocene forms.

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Set II. Early Primitive Australopithecus,
4.2-3.0 m.y.a.)

• The hominids from Laetoli and Hadar are assigned
  to Australopithecus afarensis.
• A. afarensis is so primitive in the majority of
  dental and cranial features that if it were not
  for evidence of bipedalism, this primate would
  not be classified as a hominid.

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Set III. Later, More Derived Australopithecus
(2.5-1.0 m.y.a.)

• Robust Australopithecines
• Larger body size
• Small cranial capacities
• Very large, broad faces
• Massive back teeth and lower jaws
• Gracile Australopithecines
• Different face dentition

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Set IV. Early Homo (2.4-1.8 m.y.a.)

• The earliest appearance of our genus, Homo may be
  as ancient as the robust Australopithecines.
• Leakey named these specimens Homo habilis ("handy
  man")
• H. habilis differs from Australopithecus in
  cranial cavity and dental proportions.

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Quick Quiz
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• 1. The primary task of an archeologist at a
  paleoanthropological site is to
• search for hominid "traces."
• reconstruct the ancient environment of the site.
• establish the relationships of any fossil humans
  recovered.
• perform dating techniques to establish the time
  period.

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Answer a

• The primary task of an archeologist at a
  paleoanthropological site is to search for
  hominid "traces."

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• 2. _________________ dating indicates that
  something is older or younger than something else.

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Answer Relative

• Relative dating indicates that something is older
  or younger than something else.

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• 3. The radiometric dating technique used to date
  material from a few hundred years old to 75,000
  years old is ___________.

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Answer Carbon-14

• The radiometric dating technique used to date
  material from a few hundred years old to 75,000
  years old is ___________.

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• 4. Efficient bipedalism as a primary form of
  locomotion is only seen in hominids.
• True
• False

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Answer True

• Efficient bipedalism as a primary form of
  locomotion is only seen in hominids.