chapter 8
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Chapter 8Hominid Origins
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
Chapter Outline Dating Methods Early Hominids from Africa Australopithecus from East Africa Early Homo South African Hominids Interpretations: What Does It All Mean?
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 (55–34 m.y.a.) have been discovered and now total more than 200 recognized species.
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:1. Primates2. Widely distributed3. Mostly extinct by the end of the
Eocene.
Early Eocene Primates: Features 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 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 inEarly Primate Evolution
Miocene Hominoid Distribution, From Fossils Thus Far Discovered
Miocene Fossil Hominoids1. African forms (23–14 m.y.a.)
• Especially from western Kenya, these hominoids are, in many ways, primitive.
2. 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 Hominoids3. 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 Fossils1. These are hominoids—more 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.
Miocene Hominoid Fossils4. 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.
5. 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 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 Evolutionof Hominid Characteristics
LocomotionModern 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
Mosaic Evolutionof Hominid Characteristics
BrainModern Homo
sapiens
Greatly increased brain size—highly 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 ofencephalization
Mosaic Evolutionof Hominid Characteristics
DentitionModern 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
Mosaic Evolutionof Hominid Characteristics
Toolmaking BehaviorModern 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
Unknown—no stone tools; probably had capabilities similar to chimpanzees
Revised Classificationof Hominoids
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.
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.
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).
Major Features of Hominid Bipedalism 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 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 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 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 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 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
Biological Sciences Social Sciences
Geology Physical anthropology Archaeology
Geomorphology Ecology Ethnoarchaeology
Geophysics Primatology Cultural anthropology
Chemistry Psychology
Taphonomy
Dating MethodsPaleoanthropologists 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 Chronometric Dating
Examples StratigraphyFluorine Dating
K/ArRadiocarbon (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
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.
Relative Dating Techniques Biostratigraphy - related to changes in
the dentition of animals. Paleomagnetism - based on the shifting
of the geomagnetic pole.
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.
Position of the Foramen Magnum (a) a human and (b) a
chimpanzee. Note the more
forward position in the human cranium.
Key Very Early Fossil Hominid Discoveries (pre-Australopithecus)
Site Dates(m.y.a.) Hominids
East Africa
Middle Awash (Ethiopia;
five localities)5.8–5.2 Ardipithecus
Aramis (Ethiopia) 4.4 Ardipithecus ramidus
Central Africa
Tugen Hills ~6.0 Orrorin tugenensis
Toros-Menalla ~7.0 Sahelanthropus tchadenis
Features of Australopithecus1. 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.
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.
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.
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.
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.
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.
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.
Estimated Body Weights and Stature in Plio-Pleistocene Hominids
Body Weight StatureMale 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. 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.
Steps in Interpreting Homind Evolutionary Events 5. Comparing with other fossil material—in
chronological framework if possible.6. Comparing fossil variation with known ranges
of variation in closely related groups of living primates and analyzing ancestral and derived characteristics.
7. Assigning taxonomic names to fossil material.
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.
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.
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.
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
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.
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 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 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 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) Trueb) False
Answer: True Efficient bipedalism as a primary form of
locomotion is only seen in hominids.
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