Chapter 8

Hominid 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 Hominoids

1. 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

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

Mosaic Evolutionof Hominid Characteristics

Brain

Modern 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 of

encephalization

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

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

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

GeologyPhysical

anthropologyArchaeology

Geomorphology Ecology Ethnoarchaeology

Geophysics Primatology Cultural anthropology

Chemistry Psychology

Taphonomy

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 DatingChronometric

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

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)

SiteDates

(m.y.a.)Hominids

East Africa

Middle Awash (Ethiopia;

five localities)5.8–5.2 Ardipithecus

Aramis (Ethiopia) 4.4Ardipithecus

ramidus

Central Africa

Tugen Hills ~6.0 Orrorin tugenensis

Toros-Menalla ~7.0Sahelanthropus

tchadenis

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.

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 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. 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) True

b) False

Answer: True Efficient bipedalism as a primary form of

locomotion is only seen in hominids.