The Evolution of Animals

CHAPTER 17 The Evolution of Animals Figures 17.1 – 17.3 PowerPoint® Lecture Slides for Essential Biology, Second Edition & Essential Biology with Ph...
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CHAPTER 17

The Evolution of Animals Figures 17.1 – 17.3

PowerPoint® Lecture Slides for Essential Biology, Second Edition & Essential Biology with Physiology Neil Campbell, Jane Reece, and Eric Simon

Presentation prepared by Chris C. Romero Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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.

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BIOLOGY AND SOCIETY:

INVASION OF THE KILLER TOADS • The incredible diversity of animals – Arose through hundreds of millions of years of evolution – Can be quickly threatened.

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• The Australian quoll – Is a catlike creature that preys on many small animals, such as toads.

Figure 17.1a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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THE ORIGINS OF ANIMAL DIVERSITY

• Animal life began in the Precambrian seas with the evolution of multicellular creatures that ate other organisms.

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What Is an Animal? • Animals – Are eukaryotic, multicellular, heterotrophic organisms that obtain nutrients by ingestion – Digest their food within their bodies.

Figure 17.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Most animals reproduce sexually and then proceed through a series of developmental stages.

Haploid

Sperm

Egg

2

1 Meiosis

Fertilization

Zygote (fertilized egg) Adult

3 Diploid

Blastula (cross section)

7 Metamorphosis Digestive tract

Outer cell layer Primitive (ectoderm) gut

6

5 Early gastrula

Larva Inner cell layer (endoderm) Figure 17.3

4

Later gastrula Opening

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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 protist that lived in the Precambrian seas.

Digestive cavity

Reproductive cells 1 Early colony

of protists (aggregate of identical cells)

2 Hollow

sphere (shown in cross section)

Somatic cells

3 Beginning of

cell specialization

4 Infolding

5 Gastrula-like

“protoanimal”

Figure 17.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• At the beginning of the Cambrian period, 545 million years ago, animals underwent a rapid diversification.

Figure 17.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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• What ignited the Cambrian explosion? – Many hypotheses exist.

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Animal Phylogeny • To reconstruct the evolutionary history of animal phyla, researchers must depend on clues from comparative anatomy and embryology.

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• Four key evolutionary branch points have been hypothesized.

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Sponges

Cnidarians

Flatworms Roundworms Mollusks

Annelids

Arthropods Echinoderms

Coelom from cell masses

Chordates

Coelom from digestive tube

4 Pseudocoelom

True coelom

No body cavity

3 Body cavities Radial symmetry

Bilateral 2 symmetry

True tissues

1 Multicellularity Figure 17.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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.

(a) Radial symmetry

(b) Bilateral symmetry

Figure 17.7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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• Third, the evolution of body cavities led to more complex animals.

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Body covering Tissue-filled region (from (from ectoderm) mesoderm)

• A body cavity – Is a fluid-filled space separating the digestive tract from the outer body wall

(a) No body cavity (e.g., flatworm) Pseudocoelom

– May be a pseudocoelom or a true coelom.

Body covering (from ectoderm)

Digestive tract (from endoderm) (b) Pseudocoelom (e.g., roundworm) Coelom

Figure 17.8

Digestive tract (from endoderm)

Muscle layer (from mesoderm)

Body covering (from ectoderm)

Tissue layer lining coelom and suspending Digestive tract (from Mesentery internal organs endoderm) (from (c) True coelom (e.g., annelid) mesoderm)

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• Fourth, among animals with a true coelom, there are two main evolutionary branches, which differ in embryonic development.

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MAJOR INVERTEBRATE PHYLA

• Invertebrates – Are animals without backbones – Represent 95% of the animal kingdom.

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Sponges • Phylum Porifera – Includes sessile animals once believed to be plants – Lack true tissues.

Figure 17.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The body of a sponge – Resembles a sac perforated with holes – Draws water into a central cavity, where food is collected.

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Choanocyte in contact with an amoebocyte

Pores Water flow Skeleton fiber

Central cavity Choanocyte Amoebocyte

Flagella

Figure 17.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

Gastrovascular cavity

Tentacle Mouth/anus Polyp form

Medusa form

Figure 17.11

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• Examples of polyps are – Hydras, sea anemones, and coral animals.

Figure 17.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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.

Coiled thread

Tentacle

Capsule

“Trigger” Cnidocyte Discharge of thread

Prey Figure 17.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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Flatworms • Phylum Platyhelminthes – Is represented by the simplest bilateral animals – Includes free-living forms such as planarians. Digestive tract (gastrovascular cavity)

Nerve cords

Mouth

Eyespots

Nervous tissue clusters

Figure 17.14

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• Some flatworms are parasitic Head

– Blood flukes are an example – Tapeworms parasitize many vertebrates, including humans.

Reproductive structures

Hooks Sucker

Figure 17.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Roundworms • Phylum Nematoda – Includes the most diverse and widespread of all animals – Occurs in aquatic and moist terrestrial habitats.

Figure 17.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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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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Mollusks • Phylum Mollusca – 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. Visceral mass

Coelom Mantle

Kidney

Reproductive organs

Heart

Digestive tract

Mantle cavity Radula Shell

Radula

Anus Gill

Foot

Mouth

Nerve cords

Mouth Figure 17.17

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• The three major classes of mollusks are – Gastropods, which are protected by a single, spiraled shell.

Figure 17.18a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– Bivalves, protected by shells divided into two halves.

Figure 17.18b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– Cephalopods, which may or may not have a shell.

Figure 17.18c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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Annelids • Phylum Annelida – Includes worms with body segmentation.

Anus Brain Main heart Coelom Digestive tract Segment walls

Mouth

Accessory hearts

Nerve cord Blood vessels

Excretory organ

Figure 17.19

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• There are three main classes of annelids – Earthworms, which eat their way through soil.

Figure 17.20a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– Polychaetes, which burrow in the sea floor.

Figure 17.20b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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– Leeches, some of which are parasitic.

Figure 17.20c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Arthropods • Phylum Arthropoda – Contains organisms named for their jointed appendages – Includes crustaceans, arachnids, and insects.

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General Characteristics of Arthropods • Arthropods are segmented animals with specialized segments and appendages. Cephalothorax

Abdomen

Thorax Antennae (sensory reception)

Head

Swimming appendages

Pincer (defense)

Walking legs Mouthparts (feeding)

Figure 17.21

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• The body of an arthropod is completely covered by an exoskeleton.

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Arthropod Diversity • There are four main groups of arthropods – Arachnids, such as spiders, scorpions, ticks, and mites.

Figure 17.22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– Crustaceans, such as crabs, lobsters, crayfish, shrimps, and barnacles.

Figure 17.23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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– Millipedes and centipedes.

Figure 17.24 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– Insects, most of which have a three-part body.

Head Thorax

Abdomen

Hawk moth Antenna

Forewing

Eye Mosquito

Paper wasp

Mouthparts

Hindwing

Grasshopper

Damselfly

Water strider Ground beetle

Figure 17.25

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• Many insects undergo metamorphosis in their development. (a) Larva (caterpillar) (b) Pupa (c) Pupa

(d) Emerging adult

(e) Adult

Figure 17.26

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Echinoderms • Phylum Echinodermata – Is named for the spiny surfaces of the organisms – Includes sea stars, sand dollars, sea urchins, and sea cucumbers.

Figure 17.27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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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THE VERTEBRATE GENEALOGY • Vertebrates – Are represented by mammals, birds, reptiles, amphibians, and fishes – Have unique features, including the cranium and backbone. Figure 17.28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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Characteristics of Chordates • Phylum Chordata – 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The four chordate hallmarks are – A dorsal, hollow nerve cord – A notochord – Pharyngeal slits – A post-anal tail.

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Dorsal, hollow nerve cord

Notochord

Brain Muscle segments

Mouth Anus Pharyngeal slits

Post-anal tail

Figure 17.30 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• An overview of chordate and vertebrate evolution.

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Chordates Vertebrates

Aves (birds)

Mammalia (mammals)

Reptilia (reptiles)

Amphibia (frogs and salamanders)

Hair

Silurian Devonian

Legs

Ordovician

Paleozoic

Feathers

Amniotic egg

Lungs or lung derivatives

Cambrian

Precambrian

Osteichthyes (bony fishes)

Chondrichthyes (sharks and rays)

Lancelets

Agnatha (jawless vertebrates, such as lampreys)

Tertiary

Tunicates

Cretaceous

Mesozoic

Amniotes

Carboniferous

Permian

Triassic

Jurassic

Cenozoic

Eras Periods

Tetrapods

Jaws Vertebrae

Ancestral chordate

Figure 17.31

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Fishes • The first vertebrates probably evolved during the early Cambrian period, about 540 million years ago.

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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.

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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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Most bony fishes are ray-finned fishes • A second evolutionary branch includes lungfishes and lobe-finned fishes.

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Amphibians • Members of the class Amphibia – Exhibit a mixture of aquatic and terrestrial adaptations – Usually need water to reproduce.

Figure 17.33 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Amphibians – Were the first vertebrates to colonize land – Descended from fishes that had lungs and fins with muscles.

Lobe-finned fish

Early amphibian Figure 17.34

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• Terrestrial vertebrates are collectively called tetrapods, which means “four legs”.

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Reptiles • Class Reptilia – 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Reptiles are ectotherms, which obtain their body heat from the environment.

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• Reptiles diversified extensively during the Mesozoic Era • Dinosaurs included the largest animals ever to live on land.

Figure 17.36 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Birds • Class Aves – 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.

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• A bird’s wings – Illustrate the same principles of aerodynamics as the wings of an airplane.

Ai rf o

il

Figure 17.37 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Mammals • Class Mammalia – 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.

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• There are three major groups of mammals – Monotremes, the egg-laying mammals, constitute the first group.

Figure 17.38a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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• Eutherians are also called placental mammals – Their placentas provide more intimate and longlasting association between the mother and her developing young than do marsupial placentas.

Figure 17.38c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

THE HUMAN ANCESTRY • Humans are primates.

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The Evolution of Primates • Primate evolution – Provides a context for understanding human origins.

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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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Anthropoids include – Monkeys

Figure 17.40b, c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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– Apes, the closest relatives to humans

Figure 17.40d–g Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– Humans

Figure 17.40h Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Emergence of Humankind • Humans and apes have shared a common ancestry for all but the last 5–7 million years

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Anthropoids

Prosimians

Humans

Chimpanzees

Orangutans

Gibbons

Old World monkeys

New World monkeys

Prosimians (lemurs, lorises, pottos, and tarsiers)

Gorillas

Apes

Monkeys

Ancestral primate

Figure 17.41

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Some Common Misconceptions • Our ancestors were not chimpanzees or any other modern apes • 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

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Homo sapiens Homo sapiens sapiens neanderthalensis

Homo erectus

Australopithecus boisei Australopithecus robustus

Homo habilis

Australopithecus africanus

Ardipithecus ramidus

Australopithecus afarensis

Figure 17.42 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Upright posture and an enlarged brain appeared at separate times during human evolution

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Australopithecus and the Antiquity of Bipedalism • Before there was the genus Homo, several hominid species of the genus Australopithecus walked the African savanna

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• Fossil evidence pushes bipedalism in A. afarensis back to at least 4 million years ago

Figure 17.43 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• All Australopithecus species were extinct by about 1.4 million years

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Homo habilis and the Evolution of Inventive Minds • Homo habilis, “handy-man” – Had a larger brain – Probably made stone tools

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Homo erectus and the Global Diversity of Humanity • Homo erectus was the first species to extend humanity’s range from Africa to other continents • 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 Origin of Homo sapiens • The oldest known post–H. erectus fossils – 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 the Cro-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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Homo sapiens African

European

Asian

Australasian

Interbreeding

1–2 million years ago

Homo erectus in Africa

(a) Multiregional hypothesis

Figure 17.44a

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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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Homo sapiens African

European

Asian

Australasian

100,000 years ago

Homo sapiens in Africa

(b) “Out of Africa” hypothesis

Homo erectus in Africa

Figure 17.44b

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Cultural Evolution • Culture – 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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• Second, the development of agriculture • Third, the Industrial Revolution

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EVOLUTION CONNECTION:

EARTH’S NEW CRISIS • Cultural evolution – 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

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SUMMARY OF KEY CONCEPTS • Major Invertebrate Phyla

Visual Summary 17.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• The Vertebrate Genealogy

Visual Summary 17.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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