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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
