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Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint® Lecture Slides forEssential Biology, Second Edition & Essential Biology with Physiology
Neil Campbell, Jane Reece, and Eric Simon
Presentation prepared by Chris C. Romero
CHAPTER 17CHAPTER 17
The Evolution of AnimalsFigures 17.1 – 17.3
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• Zoologists estimate that about a billion billion (1018) individual arthropods populate the Earth
• Tapeworms can reach lengths of 20 meters in the human intestine.
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• The blue whale, an endangered species that grows to lengths of nearly 30 meters, is the largest animal that has ever existed
• A reptile can survive on less than 10% of the calories required by a mammal of equivalent size.
2
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• The incredible diversity of animals
BIOLOGY AND SOCIETY:
INVASION OF THE KILLER TOADS
– Arose through hundreds of millions of years of evolution
– Can be quickly threatened.
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• The Australian quoll
Figure 17.1a
– Is a catlike creature that preys on many small animals, such as toads.
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• A non-native toad
– Was introduced from South America in 1935 to fight beetles in sugarcane fields
– Caused considerable damage to the ecosystem.
Figure 17.1b
3
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• Animal life began in the Precambrian seas with the evolution of multicellular creatures that ate other organisms.
THE ORIGINS OF ANIMAL DIVERSITY
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• Animals
What Is an Animal?
– Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion
– Digest their food within their bodies.
Figure 17.2
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• Most animals reproduce sexually and then proceed through a series of developmental stages.
Figure 17.3
EggSperm
Fertilization
Zygote (fertilized egg)
Blastula (cross
section)
Early gastrula
Later gastrula
Outer cell layer
(ectoderm)
Opening
Primitive gut
Inner cell layer (endoderm)
Larva
Digestive tract
Metamorphosis
Adult
Meiosis
Haploid
Diploid
1 2
3
4
56
7
4
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• Most animals have muscle cells and nerve cells that control the muscles.
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Early Animals and the Cambrian Explosion
• Animals probably evolved from a colonial protistthat lived in the Precambrian seas.
Figure 17.4
Reproductivecells
Somatic cells
Digestive cavity
Early colony of protists(aggregate of identical cells)
1 2 3 4Hollow sphere (shown in cross section)
Beginning of cell specialization
5 Gastrula-like “proto-animal”
Infolding
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• At the beginning of the Cambrian period, 545 million years ago, animals underwent a rapid diversification.
Figure 17.5
5
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• What ignited the Cambrian explosion?
– Many hypotheses exist.
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• To reconstruct the evolutionary history of animal phyla, researchers must depend on clues from comparative anatomy and embryology.
Animal Phylogeny
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• Four key evolutionary branch points have been hypothesized.
6
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Multicellularity
True tissues
Radial symmetry Bilateral
symmetry
No body cavity
Body cavities
PseudocoelomTrue coelom
Coelom from cell masses Coelom from
digestive tube
Figure 17.6
1
2
3
4
Sponges Cnidarians Flatworms Roundworms Mollusks Annelids Arthropods Echinoderms Chordates
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• The first branch point is defined by the presence of true tissues.
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• The second major evolutionary split is based partly on body symmetry.
Figure 17.7
(a) Radial symmetry (b) Bilateral symmetry
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• Third, the evolution of body cavities led to more complex animals.
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• A body cavity
– Is a fluid-filled space separating the digestive tract from the outer body wall
– May be a pseudocoelom or a true coelom.
Figure 17.8
(a) No body cavity (e.g., flatworm)
Body covering (from ectoderm)
Digestive tract (from endoderm)
Tissue-filled region (from mesoderm)
(b) Pseudocoelom (e.g., roundworm)
Pseudocoelom
Digestive tract (from endoderm)
Body covering (from ectoderm)
Muscle layer (from mesoderm)
(c) True coelom (e.g., annelid)
Coelom
Digestive tract (from endoderm)
Body covering (from ectoderm)
Tissue layer lining coelom and suspending internal organs (from mesoderm)
Mesentery
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• Fourth, among animals with a true coelom, there are two main evolutionary branches, which differ in embryonic development.
8
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• Invertebrates
MAJOR INVERTEBRATE PHYLA
– Are animals without backbones
– Represent 95% of the animal kingdom.
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• Phylum Porifera
Sponges
– Includes sessile animals once believed to be plants
– Lack true tissues.
Figure 17.9
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• The body of a sponge
– Resembles a sac perforated with holes
– Draws water into a central cavity, where food is collected.
9
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Figure 17.10
Pores
Water flow
Skeleton fiber
Central cavity
ChoanocyteAmoebocyte
Choanocytein contact with an amoebocyte
Flagella
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Cnidarians
• Phylum Cnidaria
– Is characterized by organisms with radial symmetry and tentacles with stinging cells.
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• The basic body plan of a cnidarian
– Is a sac with a gastrovascular cavity
– Has two variations: the sessile polyp and the floating medusa.
Mouth/anus
Tentacle
Gastrovascularcavity
Tentacle
Mouth/anus
Medusa formPolyp form Figure 17.11
10
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• Examples of polyps are
– Hydras, sea anemones, and coral animals.
Figure 17.12
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• The organisms we call jellies are medusas.
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• Cnidarians are carnivores that use tentacles armed with cnidocytes, or “stinging cells,” to capture prey.
Figure 17.13
TentacleCoiled thread Capsule
“Trigger”
Discharge of thread
Cnidocyte
Prey
11
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• Phylum Platyhelminthes
Flatworms
– Is represented by the simplest bilateral animals
– Includes free-living forms such as planarians.
Figure 17.14
Digestive tract (gastrovascularcavity) Nerve cords
Mouth
Eyespots
Nervous tissue clusters
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• Some flatworms are parasitic
– Blood flukes are an example
– Tapeworms parasitize many vertebrates, including humans.
Figure 17.15
Reproductive structures
Head
Hooks
Sucker
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• Phylum Nematoda
Roundworms
– Includes the most diverse and widespread of all animals
– Occurs in aquatic and moist terrestrial habitats.
Figure 17.16
12
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• Roundworms exhibit an important evolutionary adaptation, a digestive tube with two openings, a mouth and an anus
• A complete digestive tract can process food and absorb nutrients efficiently.
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• Phylum Mollusca
Mollusks
– Is represented by soft-bodied animals, but most are protected by a hard shell
– Includes snails, slugs, clams, octopuses, and squids, to name a few.
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• The body of a mollusk has three main parts: a muscular foot, a visceral mass, and a mantle.
Figure 17.17
Mantle
Mantle cavity
Shell
Anus
Gill
FootNerve cords
Visceral mass
Kidney
Coelom
Heart
Reproductive organs
Digestive tract
RadulaRadula
Mouth
Mouth
13
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• The three major classes of mollusks are
– Gastropods, which are protected by a single, spiraled shell.
Figure 17.18a
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– Bivalves, protected by shells divided into two halves.
Figure 17.18b
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– Cephalopods, which may or may not have a shell.
Figure 17.18c
14
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• Phylum Annelida
Annelids
– Includes worms with body segmentation.
Figure 17.19
Mouth
Brain
Accessory hearts
Main heart
Coelom
Nerve cord
Digestive tract
Blood vessels
Segment walls
Excretory organ
Anus
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• There are three main classes of annelids
– Earthworms, which eat their way through soil.
Figure 17.20a
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– Polychaetes, which burrow in the sea floor.
Figure 17.20b
15
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– Leeches, some of which are parasitic.
Figure 17.20c
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• Phylum Arthropoda
Arthropods
– Contains organisms named for their jointed appendages
– Includes crustaceans, arachnids, and insects.
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• Arthropods are segmented animals with specialized segments and appendages.
General Characteristics of Arthropods
Figure 17.21
Antennae (sensory
reception)
Pincer (defense)
Cephalothorax
Head
Thorax
Mouthparts (feeding)
Walking legs
Abdomen
Swimming appendages
16
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• The body of an arthropod is completely covered by an exoskeleton.
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• There are four main groups of arthropods
Arthropod Diversity
– Arachnids, such as spiders, scorpions, ticks, and mites.
Figure 17.22
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– Crustaceans, such as crabs, lobsters, crayfish, shrimps, and barnacles.
Figure 17.23
17
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– Millipedes and centipedes.
Figure 17.24
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Hawk moth
Mosquito Paper wasp
Damselfly Water strider
Ground beetle
Antenna
Eye
Head
Mouthparts
Thorax
Forewing
Abdomen
Hindwing
Grasshopper
– Insects, most of which have a three-part body.
Figure 17.25
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• Many insects undergo metamorphosis in their development.
Figure 17.26
(a) Larva (caterpillar)
(b) Pupa
(c) Pupa
(d) Emerging adult
(e) Adult
18
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• Phylum Echinodermata
Echinoderms
– Is named for the spiny surfaces of the organisms
– Includes sea stars, sand dollars, sea urchins, and sea cucumbers.
Figure 17.27
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• Echinoderms
– Are all marine
– Lack body segments
– Usually have an endoskeleton
– Have a water vascular system that facilitates gas exchange and waste disposal.
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• Vertebrates
THE VERTEBRATE GENEALOGY
– Are represented by mammals, birds, reptiles, amphibians, and fishes
– Have unique features, including the cranium and backbone.
Figure 17.28
19
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• Phylum Chordata
Characteristics of Chordates
– Includes the subphylum of vertebrates.
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• Other subphyla include the lancelets and tunicates, which share four key chordate characteristics.
Figure 17.29
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• The four chordate hallmarks are
– A dorsal, hollow nerve cord
– A notochord
– Pharyngeal slits
– A post-anal tail.
20
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Figure 17.30
Muscle segments
Post-anal tail
Notochord
Anus
Dorsal, hollow nerve cord
Pharyngeal slits
Brain
Mouth
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• An overview of chordate and vertebrate evolution.
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Figure 17.31
Era
sC
enoz
oic
Mes
ozoi
cP
aleo
zoic
Pre
cam
bria
nT
ert
iary
Cre
tace
ous
Jura
ssic
Tria
ssic
Pe
rmia
nC
arb
onife
rous
De
voni
an
Silu
rian
Ord
ovic
ian
Ca
mbr
ian
Tun
icat
es
Lanc
elet
s
Agn
atha
(ja
wle
ss v
erte
brat
es,
such
as
lam
prey
s)
Cho
ndric
hthy
es (
shar
ksan
d ra
ys)
Ost
eich
thye
s (b
ony
fishe
s)
Am
phib
ia (
frog
s an
d sa
lam
ande
rs)
Rep
tilia
(re
ptile
s)
Ave
s (b
irds)
Mam
mal
ia
(mam
mal
s)
Ancestral chordate
Vertebrae
Jaws
Lungs or lung derivatives
Legs
Amniotic egg
Hair
Feathers
Chordates
Vertebrates
Tetrapods
Amniotes
Per
iods
21
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• The first vertebrates probably evolved during the early Cambrian period, about 540 million years ago.
Fishes
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• These early vertebrates, the agnathans, lacked jaws
• Agnathans are represented today by lampreys.
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• The two major groups of living fishes are the classes
– Chondrichthyes
– Osteichthyes.
22
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• Cartilaginous fishes have a flexible skeleton made of cartilage
– Sharks have a lateral line system sensitive to vibrations in the water.
Figure 17.32a
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• Bony fishes
– Have a skeleton reinforced by hard calcium salts
– Have a lateral line system, a keen sense of smell, and excellent eyesight.
Figure 17.32b
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• Most bony fishes are ray-finned fishes
• A second evolutionary branch includes lungfishes and lobe-finned fishes.
23
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• Members of the class Amphibia
Amphibians
– Exhibit a mixture of aquatic and terrestrial adaptations
– Usually need water to reproduce.
Figure 17.33
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• Amphibians
– Were the first vertebrates to colonize land
– Descended from fishes that had lungs and fins with muscles.
Figure 17.34
Lobe-finned fish Early amphibian
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• Terrestrial vertebrates are collectively called tetrapods, which means “four legs”.
24
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• Class Reptilia
Reptiles
– Includes snakes, lizards, turtles, crocodiles, and alligators
– Can live totally on land.
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• Adaptations for living on land include
– Scales to prevent dehydration
– Lungs for breathing
– The amniotic egg.
Figure 17.35
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• Reptiles are ectotherms, which obtain their body heat from the environment.
25
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• Reptiles diversified extensively during the Mesozoic Era
• Dinosaurs included the largest animals ever to live on land.
Figure 17.36
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• Class Aves
Birds
– Evolved during the great reptilian radiation of the Mesozoic era
– Evolved the ability to fly.
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• Bird anatomy and physiology are modified for flight
– Bones are honeycombed, which makes them lighter
– Some specific organs are absent, which reduces weight
– A warm, constant body temperature is maintained through endothermy.
26
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• A bird’s wings
– Illustrate the same principles of aerodynamics as the wings of an airplane.
Figure 17.37
Airfoil
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• Class Mammalia
Mammals
– Evolved from reptiles about 225 million years ago
– Includes mostly terrestrial organisms.
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• Two features are mammalian hallmarks
– Hair
– Mammary glands that produce milk and nourish the young.
27
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• There are three major groups of mammals
– Monotremes, the egg-laying mammals, constitute the first group.
Figure 17.38a
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• Most mammals are born rather than hatched and are nurtured inside the mother by an organ called a placenta.
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• The second group of mammals, marsupials, are the so-called pouched mammals.
Figure 17.38b
28
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• Eutherians are also called placental mammals
– Their placentas provide more intimate and long-lasting association between the mother and her developing young than do marsupial placentas.
Figure 17.38c
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• Humans are primates.
THE HUMAN ANCESTRY
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• Primate evolution
The Evolution of Primates
– Provides a context for understanding human origins.
29
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• Primates
– Evolved from insect-eating mammals during the late Cretaceous period
• Early primates
– Were small, arboreal mammals
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• The distinguishing characteristics of primates were shaped by the demands of living in trees
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• Primate characteristics include
– Limber shoulder joints
– Eyes in front of the face
– Excellent eye-hand coordination
– Extensive parental care
Figure 17.39
30
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• Taxonomists divide primates into two main groups
– Prosimians
– Anthropoids
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• Prosimians include
– Lemurs, lorises,pottos, and tarsiers
Figure 17.40a
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• Anthropoids include
– Monkeys
Figure 17.40b, c
31
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– Apes, the closest relatives to humans
Figure 17.40d–g
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– Humans
Figure 17.40h
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• Humans and apes have shared a common ancestry for all but the last 5–7 million years
The Emergence of Humankind
32
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Figure 17.41
Prosimians Anthropoids
Monkeys ApesP
rosi
mia
ns (
lem
urs,
loris
es, p
otto
s, a
nd ta
rsie
rs)
New
Wor
ld m
onke
ys
Old
Wor
ld m
onke
ys
Gib
bons
Ora
ngut
ans
Gor
illas
Chi
m-
panz
ees
Hum
ans
Ancestral primate
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• Our ancestors were not chimpanzees or any other modern apes
Some Common Misconceptions
• Chimpanzees and humans represent two divergent branches of the anthropoid tree
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• Human evolution
– Is not a ladder with a series of steps leading directly to Homo sapiens
– Is more like a multibranched bush than a ladder
33
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Figure 17.42
Ardipithecus ramidus
Australopithecus afarensis
Australopithecus africanus
Australopithecus boisei
Australopithecus robustus
Homo habilis
Homo erectus
Homo sapiens neanderthalensis
Homo sapiens sapiens
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• Upright posture and an enlarged brain appeared at separate times during human evolution
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• Before there was the genus Homo, several hominid species of the genus Australopithecus walked the African savanna
Australopithecusand the Antiquity of Bipedalism
34
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• Fossil evidence pushes bipedalism in A. afarensisback to at least 4 million years ago
Figure 17.43
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• All Australopithecus species were extinct by about 1.4 million years
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• Homo habilis, “handy-man”
Homo habilis and the Evolution of Inventive Minds
– Had a larger brain
– Probably made stone tools
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• Homo erectus was the first species to extend humanity’s range from Africa to other continents
Homo erectusand the Global Diversity of Humanity
• The global dispersal began about 1.8 million years ago
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• Homo erectus
– Was taller than H. habilis
– Had a larger brain
– Gave rise to Neanderthals
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• The oldest known post–H. erectus fossils
The Origin of Homo sapiens
– Date back more than 300,000 years
– Are found in Africa
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• Many paleoanthropologists consider these fossils as the earliest forms of our species, Homo sapiens
• The famous fossils of modern humans from theCro-Magnon caves of France date back about 35,000 years
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• Two hypotheses regarding the origins of modern humans exist
– The multiregional hypothesis
– The “Out of Africa” hypothesis (also called the replacement hypothesis)
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• The multiregional hypothesis
– States that modern humans evolved simultaneously in different parts of the world
– States that Homo erectus spread from Africa into other continents between 1 and 2 million years ago
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Figure 17.44a
Interbreeding
1–2 million years ago
Homo sapiens
African European AsianAustral-
asian
Homo erectusin Africa(a) Multiregional hypothesis
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• The “Out of Africa” hypothesis
– States that modern humans spread out from Africa about 100,000 years ago
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Figure 17.44b
100,000 years ago
Homo sapiens in Africa
African European AsianAustral-
asian
Homo erectus in Africa(b) “Out of Africa” hypothesis
Homo sapiens
38
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• Culture
Cultural Evolution
– Is the transmission of accumulated knowledge over generations
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• Cultural evolution has had three major stages
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• First, nomads who were hunter-gatherers
– Made tools
– Created art
Figure 17.45
39
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• Second, the development of agriculture
• Third, the Industrial Revolution
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• Cultural evolution
EVOLUTION CONNECTION:
EARTH’S NEW CRISIS
– Made Homo sapiens a new force in the history of life
• Humans are changing the world faster than many species can adapt
– The rate of extinction in the twentieth century was 50 times greater than the average for the past 100,000 years
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• This rapid rate of extinction is mainly a result of habitat destruction
• The exploding human population now threatens Earth’s ecosystems
40
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SUMMARY OF KEY CONCEPTS
• Major Invertebrate Phyla
Visual Summary 17.1
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• The Vertebrate Genealogy
Visual Summary 17.2
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