ANT 3

ANCESTRAL HUMANS:
UNDERSTANDING THE HUMAN

FAMILY TREE

Chapter 6

New Human Ancestral Species

Discovery of Australopithecus sediba in 2010, and soon after,
Homo naledi in South Africa.

◦ Details remain ambiguous, but these finds represent new branches
in our family tree.

The odds of finding new species are very small, given the
scarcity of fossils.

◦ But paleoanthropology (the study the fossilized remains of ancient
hominids to shed light on their biological and behavioral evolution)
is very active right now.

◦ Advancements in genomic science and technology, including the use
of DNA evidence recovered from fossils in the lab, have had a
major influence on this field.

Excavating Australopithecus sediba
(Photo: Brent Stirton/Getty Images Reportage)

At the heart of anthropology’s interest in our human ancestors is a

key question: when, where, and how did our human ancestors

emerge, and under what conditions did modern humans evolve?

◦ Who are our earliest ancestors?

◦ What does walking on two legs and having big brains mean for us?

◦ Who were the first humans and where did they live?

◦ How do we know if the first humans were cultural beings, and what role did

culture play in their evolution?

Who Are Our Earliest Possible Ancestors?

◦ Two key issues

◦ What is our evolutionary relationship to other apes?

◦ How does that relationship affect how we view and name certain fossils found from 6

to 1 mya?

◦ All great apes and humans are placed together in Hominidae: a family of

primates that includes humans and their ancestors

Family Hominidae

◦ Hominidae has two subfamilies:

◦ Ponginae: Asian-derived subfamily; includes

Orangutan

◦ Homininae: African subfamily; includes humans,

chimpanzees, and gorillas

◦ Hominini: the tribe to which humans and our

direct human ancestors belong (hominins)

◦ All hominins are hominines

◦ But only some hominines are hominins (modern

humans and our direct lineage)

Hominins

Hominins share in common several unique

traits

◦ Modifications in the lower body, upper arms,

and backbone that make them capable of

bipedal locomotion

◦ Smaller canine teeth than other Hominidae

◦ A forward-placed foramen magnum to

support bipedalism

◦ A reduced Canine/Premolar-3 shearing

complex

General characteristics of hominins (Photo: Brent Stirton/Getty Images

Reportage)

Hominin Fossil Evidence

◦ Fossil evidence of ancestral hominins comes from Africa during the end of Miocene

◦ Numerous identifiable hominins emerged during the Pliocene and the Pleistocene

◦ Evolutionary relationships between these and earlier Miocene hominoids remains

unclear

◦ They are Australopithecus, Paranthropus, and Homo

There are three (undisputed) Hominin Genera:

◦ Australopithecus, Paranthropus, and Homo

◦ And possibly three more, including Sahelanthropus tchadensis, Orrorin tugenensis, and Ardipithecus.

Derived vs. Primitive Traits

◦ When we talk about similarities and differences between species and in terms of evolution

we talk about primitive/ancestral and derived traits

◦ Ancestral traits appear in older species of the same lineage but are retained through time

◦ Derived traits are more humanlike traits that have changed over time

Genus Australopithecus

Most researchers hypothesize that the human lineage

emerged from the australopithecines:

◦ Between 1.2-1.4m tall, fairly high degree of sexual

dimorphism, with males larger than females, and were

gracile

◦ Relatively large brains and a gripping hand

◦ May have processed food as early as 3.3 mya

◦ Arm length suggests a partially arboreal existence,

although they also had bipedal stature

Australopithecus anamensis skull (Photo: ©

Exploratorium, www.exploratorium.edu)

Genus Paranthropus

A cluster of hominin fossils dating to 2.7 and 1 mya

differ from australopithecines

◦ Larger brains, broad, “dish-shaped” faces, small foreheads,

flared cheekbones, pronounced sagittal crest, megadontia

◦ They ranged from 4.3 – 4.7 feet in height; all three species

were bipedal.

◦ Probably lived in open woodland or savannah landscapes

and were almost certainly tool users

Paranthropus aethiopicus (top/left) and Paranthropus

boisei (bottom/right) (Photos: Smithsonian

Institute; Bjørn Christian Tørrissen/Wikipedia)

Genus Homo

◦ Emerged from one australopithecine lineage about 3 to 2 mya

◦ Most hominin fossils younger than about 1.8 mya are

considered Homo

◦ Disagreement persists about how many species they actually

represent, or even if some early cases are members of Homo or

Australopithecus.

◦ Large cranial capacity, competent bipeds

◦ Made and used stone tools, called Olduwan tools

Homo naledi skull (Photo: John Hawks)

The “Missing Link”?

◦ Is one of these early species the “missing

link?” NO.

◦ Deciding which one is impossible: the fossil

record is incomplete

◦ Evolutionary theory rejects a “link”

◦ What we do have are many “missing links”

◦ Paleoanthropologists look for evolutionary

relationships between existing hominins

◦ Paleoanthropologists are still working

through who our most direct ancestor is

What Did Walking On Two Legs And Having Big
Brains Mean For The Early Hominins?

◦ Bipedalism: one of the determining traits

of hominins

◦ Directly linked with our emergence and

separation from the apes

◦ Increased brain size: also significant

◦ Enabled us to acquire a degree of social

complexity and tool use not seen in other apes

Bipedalism

Bipedalism a consequence of multiple, independent selections:

◦ It aids carrying objects

◦ It benefits hunting

◦ It allows upright reaching

◦ It aids vigilance and visual surveillance

◦ It aids long-distance walking and running

◦ It aids heat regulation

Increased Cranial Capacity

◦ Increased cranial capacity:

◦ greater brain power → increased metabolic costs for the body

◦ Increased meat consumption helped meet the added energy cost

◦ Abundance and the relative ease of gathering roots, tubers, nuts, and fatty fruits as

sources of high quality nutrition made them staple elements of Homo diets

Biocultural Evolution and Early Humans

◦ Hypothesis: bipedalism and increasing brain

power, with associated changes in diet, tool

use, and social relations, contributed to

evolutionary changes

◦ Led to the later forms of Homo

◦ If true, this hypothesis points to something

powerful and new:

◦ The interaction of biology and culture through

evolution to meet selective challenges

Who Were The First Humans And Where Did
They Live?

◦ During the Pleistocene epoch our lineage began to

spread out of Africa

◦ Homo erectus appeared about 1.8 mya

◦ Had human-like body proportions and height

◦ Lived on the ground as obligatory bipeds

◦ Cared for their young and the weak

◦ Made and used stone tools, controlled fire, may have had

some kind of proto-language

Homo erectus, female. Reconstruction based on ER

3733 by John Gurche

Homo erectus

◦ Looks a bit like us….but thicker bones, a more robust
skeleton, and a differently shaped cranium
◦ Some fossils also have a sagittal keel

◦ Found throughout Africa, Europe, India, Indonesia, and
China

◦ The taxonomic ordering of Homo erectus is unresolved; debate
continues
◦ Human-like proportions and height

◦ Obligatory bipeds

◦ Cared for the old and weak

◦ Made and used stone tools

◦ Controlled fire

◦ Possible a simple proto-language

Archaic Humans

◦ 500,000-300,000 years ago: changes in morphology and material culture suggest

emergence of one or more new variety of Homo

◦ Known for making more refined and specialized tools

◦ Individuals with these traits are referred to as archaic humans

Archaic Humans

◦ Anthropologists classify archaic

humans in one of two ways:

◦ All archaic Homo sapiens

◦ Separated into two different

species: Homo heidelbergensis and

Homo neanderthalensis

◦ The oldest archaic human

specimens are found in Africa

◦ Geographic spread includes the

Middle East, Mediterranean,

East Asia, Siberia, and Eastern

and Western Europe

Bodo cranium (Photo: © Bone Clones,

www.boneclones.com)

The Neanderthals and Denisovans

◦ Much attention has been directed to

fossils of Homo neanderthalensis

◦ Date from about 300,000 to 30,000 years

ago

◦ Stockier than modern humans, but

similar height and weight

◦ Discovery of a coeval archaic human

dating to 41,000 years in Denisova

cave adds new evidence and interest

Interrelationship of Three Species

◦ Strong fossil evidence

suggests Neanderthals,

Denisovans, and modern

humans overlapped for

10,000 years or more

◦ The relationships among

these varieties of Homo has

grown more complicated and

intriguing with technological

innovations in ancient

human genomics

Anatomically-Modern Humans

◦ 200,000 and 25,000 years ago, archaic features in

the fossil record change

◦ Changes in morphology

◦ Dramatic changes in types/complexity of tools and

other aspects of material culture and behavior

◦ Language as we know it probably appeared with

anatomically modern humans

◦ 35,000-12,000 years ago, there may have been at

least two species of humans

Where did we originate?

Where anatomically-modern humans actually originated

has led to the development of three explanatory models:

◦ The Recent African Origin model: proposes that modern

humans arose as a new species in Africa between 200,000

and 180,000 years ago, during the late Pleistocene

◦ The Multiregional Evolution model: proposes that modern

humans are only the most recent version of a single species,

Homo sapiens, that had been in Africa, Asia, and Europe for

nearly 2 million years.

◦ The Multiple Dispersals model (MD): argues that modern

humans left Africa in multiple waves, and edges out the

others given the current fossil and DNA evidence. In this

model the initial movement out of Africa occurs

approximately 1.8 mya.

How Do We Know If The First Humans Were
Cultural Beings, And What Role Did Culture Play In

Their Evolution?

◦ Cultural capacity of hominids emerged over a

long time and interacted with biology to meet

selective demands through biocultural

evolution

◦ Humans approached environmental

challenges with more than their hands and

teeth during the Paleolithic

Changes During the Paleolithic

Beginning with Homo erectus, we know culture played a greater role in their lives

than earlier hominins because:

◦ Diets changed: Increased brain and body size meant higher metabolic rates, requiring more

and higher-quality food.

◦ Tools changed: Early Homo used Olduwan tools, allowing processing of animals and

plants. About 1.6-1.4 mya, Acheulean tools, with better edges and different styles, appear in

the fossil record

◦ Used fire: enables consumption of a wider variety of foods and a higher energy return on

foods eaten and marks the beginning of cooking

◦ Cooperative behaviors increased: increases survivability

The Material Culture and Behavior of Archaic Humans

Evidence for archaic human material culture

and behavior:

◦ More complex tools appear

◦ Evidence of organized group hunts

◦ Regular use of controlled fire

◦ Evidence of shelters of wood and possibly hide

◦ 200,000 years ago, the Levallois toolmaking

technique appears

The Significance of Culture

◦ Cannot say with certainty when it

appeared

◦ Human activity is based on social

interdependence and intensive cooperation,

which depends on communication

◦ Cultural meanings allow for group memory,

establishing patterned ways of doing things,

and metaphysical thought

◦ By 50,000 years ago, anatomically modern

humans created images that some

scholars interpret as art