Chapter 8
Hominid Origins
Chapter Outline
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Early Primate Evolution
Miocene Fossil Hominids
Definition of Hominid
The Bipedal Adaptation
Biocultural Evolution: The Human
Capacity for Culture
Paleoanthropology as a Multidisciplinary
Science
Chapter Outline
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Dating Methods
Early Hominids from Africa
Australopithecus from East Africa
Early Homo
South African Hominids
Interpretations: What Does It All Mean?
Early Primate Evolution
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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 (55–34 m.y.a.) have been discovered
and now total more than 200 recognized
species.
Eocene Primates
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Fossil primates from the Eocene display
distinctive primate features.
Looking at the whole array of Eocene
primates, it is certain that they were:
1. Primates
2. Widely distributed
3. Mostly extinct by the end of the
Eocene.
Early Eocene Primates:
Features
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Chinese fossils dating from the early Eocene
(55–45 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.
Oligocene Primates
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The Oligocene (34–23 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.
Major Events in
Early Primate Evolution
Miocene Hominoid Distribution,
From Fossils Thus Far Discovered
Miocene Fossil Hominoids
1.
2.
African forms (23–14 m.y.a.)
•
Especially from western Kenya, these
hominoids are, in many ways, primitive.
European forms (16–11 m.y.a.)
•
From scattered localities in France, Spain,
Italy, Greece, Austria, Germany, and
Hungary, most are quite derived.
Miocene Fossil Hominoids
3.
Asian forms (16–7 m.y.a.)
•
The largest and most varied group from
Turkey through India/Pakistan and east to
southern China, most are highly derived.
Miocene Hominoid Fossils
1.
2.
3.
These are hominoids—more closely related to
the ape-human lineage than Old World
monkeys.
Mostly large-bodied hominoids, more akin to
the lineages of orangutans, gorillas,
chimpanzees, and humans than smallerbodied apes.
Most of the Miocene forms thus far discovered
are so derived that they are probably not
ancestral to any living form.
Miocene Hominoid Fossils
4.
5.
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.
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.
Patterns of Evolution
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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.
Mosaic Evolution
of Hominid Characteristics
Modern
Homo
sapiens
Early
hominid
Locomotion
Bipedal: shortened pelvis; body size larger;
legs longer; fingers and toes not as long
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, Quadrupedal: long pelvis; some capable of
generalized considerable arm swinging, suspensory
hominoid locomotion
Mosaic Evolution
of Hominid Characteristics
Modern
Homo
sapiens
Early
hominid
Brain
Greatly increased brain size—highly
encephalized
Larger than Miocene forms, moderately
encephalized; prior to 6 m.y.a., no more
encephalized than chimpanzees
Miocene, Small compared to hominids, but large
generalized compared to other primates; a fair degree of
hominoid encephalization
Mosaic Evolution
of Hominid Characteristics
Modern
Homo
sapiens
Early
hominid
Dentition
Small incisors; canines further reduced;
molar tooth enamel caps thick
Moderately large incisors; canines somewhat
reduced; molar tooth enamel caps very thick
Miocene, Large front teeth (including canines); molar
generalized teeth variable, depending on species; some
hominoid have thin enamel caps, others thick enamel
caps
Mosaic Evolution
of Hominid Characteristics
Toolmaking Behavior
Modern
Stone tools found after 2.5 m.y.a.; increasing
Homo
trend of cultural dependency apparent in
sapiens
later hominids
Early
In earliest stages unknown; no stone tool
hominid
use prior to 2.5 m.y.a.; more oriented toward
tool manufacture and use than chimpanzees
Miocene, Unknown—no stone tools; probably had
generalized capabilities similar to chimpanzees
hominoid
Revised Classification
of Hominoids
The Bipedal Adaptation
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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.
Obligate Bipedalism
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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.
Major Features of Hominid
Bipedalism
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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).
Major Features of Hominid
Bipedalism
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The spine has two
distinctive curves—a
backward (thoracic) one
and a forward (lumbar)
one—that keep the trunk
(and weight) centered
above the pelvis.
Major Features of Hominid
Bipedalism
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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.
Major Features of Hominid
Bipedalism
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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%).
Major Features of Hominid
Bipedalism
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The femur is angled
inward, keeping the legs
more directly under the
body; modified knee
anatomy also permits full
extension of this joint.
Major Features of Hominid
Bipedalism
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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.
Paleoanthropology
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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.
Components of
Paleoanthropology
Physical
Sciences
Geology
Biological
Sciences
Physical
anthropology
Social Sciences
Archaeology
Geomorphology
Ecology
Ethnoarchaeology
Geophysics
Primatology
Cultural anthropology
Chemistry
Taphonomy
Psychology
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.
Relative and Chronometric
Dating
Relative Dating
Examples
Stratigraphy
Fluorine Dating
Methodological Provides a
basis
sequence only; i.e.,
no estimates in
actual number of
years
Chronometric
Dating
K/Ar
Radiocarbon (14 C)
Fission-track
Most techniques*
are radiometric;
i.e., steady decay
of radioactive
isotope provides
estimate in actual
number of years
Relative Dating Techniques
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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.
Relative Dating Techniques
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Biostratigraphy - related to changes in
the dentition of animals.
Paleomagnetism - based on the shifting
of the geomagnetic pole.
Chronometric Dating
Techniques
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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.
Position of the Foramen
Magnum
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(a) a human and (b) a
chimpanzee.
Note the more
forward position in
the human cranium.
Key Very Early Fossil Hominid
Discoveries (pre-Australopithecus)
East
Africa
Central
Africa
Site
Dates
(m.y.a.)
Hominids
Middle Awash
(Ethiopia;
five localities)
5.8–5.2
Ardipithecus
Aramis (Ethiopia)
4.4
Ardipithecus
ramidus
Tugen Hills
~6.0
Orrorin tugenensis
Toros-Menalla
~7.0
Sahelanthropus
tchadenis
Features of Australopithecus
1.
2.
3.
They are all clearly bipedal (although not
necessarily identical to Homo in this
regard).
They all have relatively small brains (i.e.,
at least compared to Homo).
They all have large teeth, particularly the
back teeth, with thick to very thick
enamel on the molars.
Laetoli
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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.
Hadar (Afar Triangle)
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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.
Koobi Fora
(East Lake Turkana)
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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.
West Turkana
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Two important discoveries:
 Discovery of a nearly complete 1.6
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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.
Olduvai Gorge
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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.
South African Sites
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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.
Estimated Body Weights and Stature in
Plio-Pleistocene Hominids
Body Weight
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 African
“robust”
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.
Steps in Interpreting Homind
Evolutionary Events
1.
2.
3.
4.
Selecting and surveying sites.
Excavating sites and recovering fossil
hominids.
Designating individual finds with
specimen numbers for clear reference.
Cleaning, preparing, studying, and
describing fossils.
Steps in Interpreting Homind
Evolutionary Events
5.
6.
7.
Comparing with other fossil material—in
chronological framework if possible.
Comparing fossil variation with known ranges
of variation in closely related groups of living
primates and analyzing ancestral and derived
characteristics.
Assigning taxonomic names to fossil material.
Groups of
Plio-Pleistocene Hominids
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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.
Set I. Basal Hominid
(4.4 m.y.a.)
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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.
Set II. Early Primitive
Australopithecus, 4.2-3.0 m.y.a.)
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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.
Set III. Later, More Derived
Australopithecus (2.5-1.0 m.y.a.)
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Robust Australopithecines
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Larger body size
Small cranial capacities
Very large, broad faces
Massive back teeth and lower jaws
Gracile Australopithecines
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Different face dentition
Set IV. Early Homo
(2.4-1.8 m.y.a.)
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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.
Quick Quiz
1. The primary task of an archeologist at a
paleoanthropological site is to
a) search for hominid "traces."
b) reconstruct the ancient environment
of the site.
c) establish the relationships of any
fossil humans recovered.
d) perform dating techniques to establish
the time period.
Answer: a
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The primary task of an archeologist at a
paleoanthropological site is to search
for hominid "traces."
2. _________________ dating indicates
that something is older or younger than
something else.
Answer: Relative
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Relative dating indicates that something
is older or younger than something else.
3. The radiometric dating technique used to
date material from a few hundred years
old to 75,000 years old is ___________.
Answer: Carbon-14
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The radiometric dating technique used to
date material from a few hundred years
old to 75,000 years old is ___________.
4. Efficient bipedalism as a primary form of
locomotion is only seen in hominids.
a) True
b) False
Answer: True
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Efficient bipedalism as a primary form of
locomotion is only seen in hominids.