Transcript PowerPoint lecture - Lower Cape May Regional School District

Chapter 26
Human Evolution
Albia Dugger • Miami Dade College
26.1 A Bit of a Neanderthal
• Paleoanthropology is the scientific study of prehistoric
humans and their relatives
• Neanderthals (Homo neanderthalensis) lived in the Middle
East, Europe, and in central Asia as far east as Siberia
• They had a short, stocky build, a long, low braincase, and
pronounced brow ridges
• DNA studies show that Neanderthal genes exist in several
groups of modern humans (Homo sapiens)
Neanderthal and Modern Human
Svante Pääbo with
a reconstructed Neanderthal Skull
26.2 Primates: Our Order
• Primates are an order of placental mammals that includes
humans, apes, monkeys, and close relatives
• Primate characteristics:
• Hands and feet capable of grasping
• Eyes at the front of the head
• Large brains with expanded regions for vision and
information processing
• Varied diet; four types of teeth
• Provide extensive care to young
Origins and Early Branchings
• Primates branched into wet-nosed (Strepsirrhini) and drynosed primates (Haplorhini) about 50 million years ago
• Anthropoids include monkeys, apes, and humans
• New World monkeys are climbers with long, prehensile tails
that help them maintain balance
• Old World monkeys are larger and have no prehensile tail –
many spend their lives on the ground
• Apes and humans are tailless hominoids
Nonanthropoid Primates: Lemur
Nonanthropoid Primates: Tarsier
Nonanthropoid Primates: New World Monkey
Nonanthropoid Primates: Old World Monkey
Take-Home Message:
What are primates?
• Primates include lemurs, tarsiers, monkeys, apes, and
humans. Most primates are tree-dwellers. Traits such as a
flexible shoulder joint and grasping hands with nails are
adaptations to a climbing lifestyle.
• Compared to other mammals, primates have a relatively large
brain with more area devoted to vision and less to smell.
• There are two main subgroups. Lemurs and their relatives
belong to the subgroup with a wet nose and a fixed upper lip.
Tarsiers, monkeys, apes, and humans belong to the subgroup
with a dry nose and a movable upper lip.
ANIMATED FIGURE: Primate evolutionary
tree
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26.3 The Apes
• Hominoids are tailless primates with an upright posture and
relatively large brains
• They branched off from a common ancestor with Old World
monkeys about 30 million years ago
• Proconsul species lived in North Africa about 20 mya
• In the Miocene, new species evolved and dispersed to
Europe and Asia
Modern Apes
• Gibbons (lesser apes) are small apes with elongated arms
that inhabit Southeast Asian forests
• Great apes include the Asian orangutan and African gorillas,
chimpanzees, and bonobos
• Gorillas (Gorilla gorilla), the largest living primates, live in
forests and feed mainly on leaves
• Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus),
are our closest living relatives
Gibbon
Orangutan
Gorilla
Chimpanzee
A Human–Ape Comparison
• Only members of the lineage leading to humans are bipedal
– adapted to walking upright
• The human backbone has an S-shaped curve that keeps the
head centered over the feet
• Human feet have a pronounced arch and a non-opposable
big toe
•
An ape’s spinal cord enters the skull’s base near the rear –
a human spinal cord enters near the center
spinal cord
attaches at
rear of skull
C-shaped
curve in
backbone
legs shorter
than arms,
thighs angle
outward
flat foot with
opposable big toe
Figure 26-5a p443
spinal cord
attaches at
center of skull
S-shaped
curve in
backbone
legs longer
than arms,
thighs angle
inward
foot with arch,
big toe aligned
with other
toes and not
opposable
Figure 26-5b p443
ANIMATED FIGURE: Primate skeletons
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A Human–Ape Comparison (cont.)
• A human thumb is longer, stronger, and more maneuverable
than that of a chimpanzee
• Many monkeys and apes grasp objects in a power grip, but
only humans routinely use a precision grip for fine
manipulation of objects
Power Grip and Precision Grip
power grip
precision grip
A Human–Ape Comparison (cont.)
• The lineage leading to humans underwent a great expansion
of the brain
• A human brain is three times the size of a chimpanzee brain
• The human brain also grows for a longer period after birth,
and our offspring receive extended parental care
chimpanzee
Figure 26-6a p443
underside of skulls
Figure 26-6b p443
human
Figure 26-6a p443
underside of skulls
Figure 26-6c p443
Take-Home Message: Which human traits are
typical of hominoids and which are novel?
• Hominoids share a common ancestor with Old World
monkeys, but they are generally larger than monkeys, lack a
tail, and have an upright stance. Modern hominoids include
Asian apes, African apes, and humans.
• Upright walking (bipedalism) evolved in the lineage leading to
humans. This lineage also shows a trend toward a more
maneuverable thumb, a larger and more complex brain, and a
longer period of postnatal development.
26.4 Rise of the Hominins
• Hominins are the lineage of humans and all extinct species
more closely related to humans than to any other group
• Bipedalism is a defining hominin trait – researchers studying
hominin origins look for evidence of upright walking
• Sahelanthropus tchadensis, 7 mya, western Africa
• Orrorin tugenensis, 6 mya, East Africa
• Ardipithecus species, 5.8 to 5.2 mya, East Africa
The Hominins
Sahelanthropus tchadensis
Orrorin tugenensis
Ardipithecus kadabba
Ardipithecus ramidus
Australopithecus anamensis
Australopithecus afarensis
Australopithecus africanus
Paranthropus boisei
Homo habilis
Homo erectus
Homo neanderthalensis
Homo floresiensis
Homo sapiens
7
6
5
4
3
Millions of years ago
2
1
Ardipithecus ramidus
Australopiths
• Australopiths include two genera of hominins that lived in
Africa from 4 to 1.2 mya
• Australopithecus afarensis lived in Tanzania and other parts
of eastern Africa from 3.9 to 3 mya
• Footprints indicate that this species had a pronounced arch
and a big toe in line with the other toes
• A partial skeleton known as Lucy is the best known
representative of this species
Bipedal Footprints, 3.6 MYA
Lucy (Australopithecus afarensis)
Paranthropus
• Paranthropus descended from an Australopithecus ancestor
• Strong teeth and heavily muscled jaws allowed Paranthropus
to eat hard and fibrous foods
• Paranthropus species are considered close relatives of early
humans, but not possible ancestors
Australopithecus africanus
Paranthropus boisei
ANIMATED FIGURE: Fossils of
australopiths
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Factors Favoring Bipedalism
• Bipedal walkers move more efficiently across open ground
than chimpanzees who move on all fours
• Bipedalism keeps the body cooler
• An upright stance makes it easier to see predators
• Free hands can be used to gather food and carry it from place
to place
Take-Home Message:
What are hominins?
• Hominins include modern humans and extinct members of
their lineage.
• Possible hominin fossils date back as far as 7 million years
ago. Early hominins had small brains. Australopiths are a
diverse group of African hominins that probably include
human ancestors.
26.5 Early Humans
• When classifying fossil s, scientists who are “lumpers” look
for similarities and assign fossils to relatively few species
• Scientists who are “splitters” focus on differences and often
name new species on the basis of subtle differences
• Lumpers place the earliest fossil evidence of our genus,
Homo, in two species – splitters divide them into four or more
Homo habilis
• Humans are members of the genus Homo
• The oldest species is Homo habilis (2.3 mya), though some
scientists classify them as a species of Australopithecus
• It overlapped in eastern Africa both with australopiths and at
least one other species of Homo
Homo habilis
Homo habilis and Australopiths
Homo erectus
• Homo erectus appears in the fossil record about 1.8 mya
• H. erectus stood on legs that were longer than its arms and
had a relatively big brain
• H. erectus left Africa and colonized Indonesia by 1.6 million
years ago, and China by 1.15 million years ago
• Some scientists split Homo erectus fossils into two species:
H. erectus in Asia, and H. ergaster in Africa
Homo erectus
Early Culture
• Culture is a set of learned behaviors passed from one
individual to another, and from one generation to the next
• The earliest hominin cultural trait for which we have fossil
evidence is toolmaking, probably by australopiths
• H. erectus used stone tools to cut up animal carcasses, to
scrape meat from bones, and to extract marrow
Homo erectus and Stone Tools
Communication
• H. habilis and H. erectus probably used gestures and calls to
communicate
• Thus far, scientists have not found fossil evidence of
anatomical modifications necessary for spoken language in
either early species of Homo
Take-Home Message:
What traits characterized early humans?
• Homo habilis is the most ancient human species known. It
lived in Africa and was similar in many respects to
australopiths, but its hands and arms more closely resemble
those of modern humans
• Homo erectus is known from Africa, Europe, and Asia. It had
a significantly larger brain than earlier hominins. Females
had a pelvis that facilitated birth of offspring with large heads.
• Early humans made stone tools and used them to cut up
animal carcasses. Stone tool use may have begun among the
australopiths.
26.6 Recent Human Lineages
• A 195,000-year-old fossil from Ethiopia is the earliest
evidence of our species, Homo sapiens
• Compared to H. erectus, we have a higher, rounder skull, a
larger brain, flatter face, and smaller jawbones and teeth
• We also have a chin, a protruding area of thickened bone in
the middle of our lower jawbone
Origin of Homo Sapiens
• Multiregional model: Populations of H. sapiens in different
regions evolved from H. erectus in those regions – with gene
flow between populations
• Replacement model: H. sapiens evolved in Africa, then
migrated to different regions and replaced other hominins in
those regions
• Genomic studies of global populations support the
replacement model
Two Models for the Origin of H. sapiens
H. erectus
H. sapiens
Africa
Asia
Europe
H. erectus
H. sapiens
Africa
Asia
Europe
Time
Dispersal of Homo Sapiens
• Fossils and genetic evidence allow scientists to trace human
dispersal routes
• About 15,000 years ago, humans crossed land bridge that
connected Siberia with North America
• Humans devised cultural means to survive in inhospitable
environments
• A capacity for modifying the habitat and for language aided
our cultural evolution
Dispersal Routes of Homo sapiens
Premodern Homo Species
• Recent findings suggest that modern humans coexisted with
another hominin, Homo floresiensis
• Some scientists think these fossils could actually be H.
erectus, H. sapiens, or australopiths
• Further study of fossils and possibly DNA analysis will help
test the competing hypotheses
Take-Home Message: How are the most
recently evolved hominins related?
• Both modern humans and Neanderthals are descendants of
H. erectus.
• Modern humans originated in Africa, then dispersed into other
regions. Early in this dispersal, humans entered the Middle
East and mated with Neanderthals they encountered there.
• A recently discovered Indonesian hominin has been named
Homo floresiensis, but its ancestry and relationship to other
species remain a matter of investigation
ANIMATION: Genetic distance between
human groups
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