Chapter 17: Human Evolution
17-1 The Study of Human Origins
17-2 Fossil Evidence of Hominid Evolution
17-3 Hypotheses of Hominid Evolution
17-1 The Study of Human Origins
I. The Hominid Fossil Record (understanding HUMAN evolution)
• (1) Revealing our ANCESTRY through FOSSIL records, and
• (2) Investigating closest of our living kin (primates).
NOTE: Some human behavior AND morphology are SIMILAR to those
of other PRIMATES, HOWEVER some remain UNIQUELY human.
(1) Paleoanthropologists (a.ka., biological anthropologists)
• Uncover FOSSIL EVIDENCE (including TOOLS, bones of PREY, and
PLANT remains) used to support LIFESTYLES of human ancestors.
(2) Hominids (hominid evolution)
• Modern humans AND our most recent ancestors;
NOTE: FOSSIL EVIDENCE largely pertains to skulls, teeth, bone
fragments, AND also tools (in the more recently evolved hominids).
(3) Pelvis (anatomical EVIDENCE for hominid evolution)
• Bones MAKING up the “HIPS” are evidence in SHOWING whether or not
an organism can walk UPRIGHT (bipedalism).
II. Primate Characteristics (Order Primata, Class Mammalia)
• 2 groups are RECOGNIZED…
(1) Anthropoid primates
(2) Prosimian primates
• NOTE: ALL primates evolved GRASPING hands, acute COLOR vision,
FRONT-facing eyes (depth perception) & proportionately LARGE brains.
(1) Anthropoid Primates (majority are GROUND species)
• MORE-RECENTLY evolved e.g., marmosets, gibbons, monkeys, apes,
and humans.
(2) Prosimian Primates (majority of species are ARBOREAL)
• MORE-PRIMITIVE and ANCESTRAL primates e.g., lemurs, lorises, and
tarsiers.
(3) Prehensile (adaptation of primate DEXTERITY)
• Movable fingers and toes (GRASPING using hands and feet) 
ancestral CLAWS have become MODIFIED as flattened NAILS.
(A) Characteristics of Anthropoids (rotating shoulder and elbow joints)
• Better DEXTERITY, LARGER and more COMPLEX brain (than prosimians),
IMPROVED color vision (evolved with being DIURNAL).
(1) Opposable Thumb (human evolution  LOST opposable big toe)
• 2-jointed thumb OPPOSITE to other fingers—allows for a NEW
arrangement of fingers better for PRECISION.
(2) Dental Formula (humans and anthropoids SHARE this arrangement)
• Includes 2 pairs of INCISORS, 1 pair of CANINES, 2 pairs of PREMOLARS, and 3 pairs of MOLARS.
(3) Great Apes (Modern Apes; Chimpanzee and Human = ~98% DNA)
• Gibbons, orangutans, gorillas, and chimpanzees  LARGER cranial
capacity  MORE complex structure (similar to HUMAN evolution).
NOTE: As primates evolved FROM prosimian TO anthropoid, brain SIZE
increased, allowing for complex behaviors and BETTER adaptability)
(B) Characteristics of Humans (Morphological distinctions)
• We are distinguished FROM the great apes in SEVERAL ways, including…
(1) Human jaw is ROUNDER rather than NARROW U-shaped like great apes
(2) Human pelvis is CUP-shaped rather than the FLATTER ape pelvis.
(3) Human spine is S-SHAPED rather than the SINGLE curve of ape spine.
(4) Human foot has SHORT, ALIGNED toes rather than the longer,
grasping toes (and opposable, big toe) of the ape.
NOTE:
Characteristics 2-4 work together to support
FULL TIME BIPEDALISM in humans;
(ONLY MAMMALS CAPABLE OF BIPEDALISM).
Critical Thinking
(1) When analyzing fossils, scientists examine the foramen magnum, the
opening for the spinal cord in the base of the skull. What does the
location of the foramen magnum on a skull tell about the posture of an
animal?
(1) Bipedalism (defines the Hominid lineage, from QUADRUPEDAL)
• An adaptation to GRASSLANDS  ability to walk primarily on TWO
legs, a UNIQUELY human trait.
NOTE: An ENLARGEMENT of human BRAIN has been shown to hold
extensive areas devoted to production and understanding of SPEECH—
important for cultural and intellectual development.
17-2 Fossil Evidence of Hominid Evolution
I. The First Hominids (evidence of bipedalism separates PRE-hominids)
• Hominid gene pool has EVOLVED towards a LARGER BRAIN and
BIPEDALISM
(e.g., improved vision, freed-up forelimbs).
NOTE: Fossils of hominids, UNLIKE those of apes (PRE-hominids) and their
ancestors, show ADAPTATIONS for UPRIGHT walking.
(1) Quadrupedal (advantages VS. disadvantages)
• Modern NON-human anthropoids walk on FOUR limbs (anatomy varied).
NOTE: Recent fossil evidence (on A. afarensis) has SUPPORTED a belief
that UPRIGHT walking evolved BEFORE any other adaptation (i.e., did NOT
require a LARGE brain) making hominids UNIQUE among anthropoids.
II. Australopithecus (a hominid GENUS)
• 1974: 3 m.y.o. PARTIAL skeleton of a PRIMATE found in the Afar Valley
of eastern Africa by Donald Johanson.
NOTE: Fossil named Australopithecus afarensis (A. afarensis)—southern
APE of the Afar Valley. Fossil was nicknamed Lucy, (estimated to be 3.03.9 m.y.o.)
(1) Lucy (hominid fossil ~ 3.2 m.y.a., ~ 475 cc  skull )
• Smaller CRANIAL CAPACITY (than humans) ALSO with SHORTER
stature than humans (~ Lucy was the HEIGHT of a chimpanzee).
(A) Other Australopithecines (different hominids COEXISTED (same TIME)
*(ANCESTOR) A. anamensis (~3.5 m.y.a.  OLDER than Lucy?)—A possible
ancestor of Lucy, found in 1995; presence of a SHINBONE may indicate
*BIPEDALISM*.
(DESCENDANT) A. africanus (2.3-3.0 m.y.a.)—A possible DESCENDANT of
Lucy, taller/heavier with a slightly LARGER cranial capacity (~430-550 cc).
(DESCENDANT) A. robustus and A. boisei (1.0-2.6 m.y.a.)—More RECENT
descendant (BUT non-human) HEAVY and LARGE SKULLS and larger
TEETH (~450-600 cc).
(B) An Older Hominid? (1995 uncovered an OLDER hominid)
• A NEW GENUS that predates Australopithecus by 200,000 years—
Ardipithecus ramidus, a *BIPEDAL* and the EARLIEST FOUND hominid.
• NOTE: Human evolutionists do NOT believe human evolution occurred in
a SINGLE, uninterrupted parade of increasingly humanlike forms.
• Rather evidence suggests SEVERAL hominid forms arose AND some died
out, leaving NO descendants. Thus the HUMAN EVOLUTIONARY TREE
contains many branches (like a BUSH).
17-3 Hypotheses of Hominid Evolution
NOTE: As RESEARCH continues, we are observing DEAD-END branches of
human evolution AND evidence that DIFFERENT hominids COEXISTED.
I. Early Members of Homo, The Human Genus (20th century fossils)
• HUMAN-LIKE morphology resulted in NEW human genus, Homo 
(1) LARGER Cranial Capacity (700 CC),
(2) TOOL Use.
(A) Homo habilis (“handy human,” tool MARKS on animal bones)
• 1.6-2.5 m.y.a.:  1st to make tools and weapons (also have larger SKULL)
(B) Homo erectus (“upright human” 1.8 m.y.a. to 50,000 years ago)
• Believed to be 1st hominid OUT of Africa  fossils of “Java Man” found
on Island of Java (Pacific) (also Europe, Asia).
NOTE: Compared to MODERN humans, H. erectus had a thick skull, large
brow ridges, a low forehead, and large protruding teeth. To survive in
COLDER climates of Europe and Asia, H. erectus may have used FIRES in
caves for warmth and cooking.
II. Homo sapiens (include TWO lineages  Neanderthal and Cro-Magnon)
• Descended FROM H. erectus ~ 800,000 years ago.
(Existed until as recently as 50,000 to 35,000 years ago).
NOTE: When H. sapiens AROSE, it is possible they did NOT replace H.
erectus RIGHT AWAY. Findings (fossils) show coexistence of BOTH
SPECIES may for occurred for ~ 700,000 years.
(A) Neanderthals (LARGEST C.C.,  evidence of STONE TOOLS for skins)
• EARLIEST group of H. sapiens from around 230,000-30,000 y.a. and
were found in parts of Europe and Asia.
NOTE: Heavy bones, THICK brow ridges, protruding teeth, AND a very
LARGE cranial capacity (larger than modern humans?!)—Are NOT believed
to be ancestral to modern humans and DISAPPEARED (LEFT NO
DESCENDANTS) at the same time that MODERN H. sapiens evolved in
LARGE numbers. (possible tribal warfares OR disease?)
Critical Thinking
(2) According to existing fossil evidence, Neanderthals died out about
30,000 years ago. Some anthropologists hypothesize that the
Neanderthals were killed off by Cro-Magnons. Others hypothesize what
the two groups interbred. What evidence would you look for to evaluate
these two hypotheses?
(B) Homo sapiens (MODERN  BETTER-developed tools/weapons)
• 1st fossils to bear RESEMBLANCE to modern humans  found in
southwestern FRENCH CAVES  ~ 35,000 years old. (Cro-Magnons)
NOTE: Cro-Magnons are distinguished from Neanderthals by their
HIGHER forehead and RECESSED brow ridge and teeth; also stood
TALLER at about 6 feet tall (ADVANCED use of TOOLS).
• OLDEST modern H. sapiens fossils are about 100,000 years old and
were found in Africa—BUT as Neanderthals declined, modern H. sapiens
became MORE advanced in hunting, habitat-building, and survival.
Critical Thinking
(3) How might the acquisition of language account for the very fast
cultural and intellectual development that has occurred in the evolution of
humans?
III. Spread of Modern Humans (TWO theories)
• ALL modern humans belong to a SINGLE species, Homo sapien sapien;
So HOW did all of our genetic VARIATION arise OVER TIME?
Critical Thinking
(4) From H. habilis to modern H. sapiens, there has been a trend for brain
size to increase. Is it inevitable that any future descendant species of H.
sapiens will have larger brains than we have? Explain your answer in terms
of some form of natural selection, such as directional selection.
(A) Multiregional Evolution (LESS widely accepted)
• Gene FLOW existed AMONG different populations during TRANSITION
from H. erectus  H. sapiens.
(1) Multiregional Hypothesis of Human Evolution [1 MILLION years AGO]
• PARALLEL populations of H. sapiens evolved SIMULTANEOUSLY from
DIFFERENT H. erectus populations LOCATED around the WORLD.
(A) Out of Africa (MORE widely accepted, mitochondrial DNA)
• MODERN H. sapiens originated about [100,000 to 200,000] years ago and
then, LIKE H. erectus before them, LEFT Africa to colonize the WORLD.
(1) Recent African-Origin Hypothesis (supported by mitochondrial DNA)
• MODERN H. sapiens evolved IN Africa and SPREAD throughout the
world, REPLACING populations of H. erectus and EARLY H. sapiens.
Critical Thinking
(5) Compared with humans, apes do not have a well-developed voice box or
well-developed facial muscles. How might the ape’s anatomy affect its
ability to use spoken language?
Extra Slides AND Answers for Critical Thinking Questions
(1) In social groups with language, information can be passed on and
accumulated, which significantly speeds up cultural and intellectual
development.
(2) The location of the foramen magnum indicates the angle at which the
spinal cord exits the skull, a clear indicator of posture.
(3) Fossil evidence of Neanderthals who met a violent death in areas where
Cro-Magnons later flourished would constitute evidence that the
Neanderthals were killed off by Cro-Magnons. Fossil evidence of a body
type representing a blend of Neanderthals and Cro-Magnon features would
support the hypothesis that the two groups interbred.
(4) It is not inevitable that descendant species of H. sapiens will have
larger brains that modern humans. Stabilizing selection tends to keep
traits in an average range. The size of the human female pelvis must
enlarge along with any enlargment of the head.
(5) The ape’s anatomy would restrict its ability to use spoken language
because speed production requires a great degree of control of the voice
box and facial muscles.
Revisiting Evolution
• Evolutionary theory holds that the organisms alive on Earth
today, including humans, evolved from shared ancestors.
• During their evolution, populations acquired characteristics
that distinguished them from their ancestors and from other
populations alive today.
Assessing Prior Knowledge
• What theories are there about how new species form? And what
are the criteria for becoming a new species?
• Distinguish between “species” and “race,” with respect to human
populations.