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CHAPTER 17
The Evolution of Animals
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society:
You’re Going to Treat Me With What?!
• In January 2004, the U.S. Food and Drug
Administration (FDA) did something it had never
done before.
– It approved the use of a live animal as a medical
device.
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• Doctors were given permission to use juvenile
blowflies to cleanse infected wounds.
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Figure 17.1a
• The FDA also approved the use of leeches for the
treatment of circulatory complications.
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Figure 17.1b
The Origins of Animal Diversity
• Animal life began in 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.
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Figure 17.2
• Most animals reproduce sexually and then proceed
through a series of developmental stages.
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Figure 17.3
• Most animals have muscle cells, as well as nerve
cells that control the muscles.
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Early Animals and the Cambrian Explosion
• Animals probably evolved from a colonial
flagellated protist that lived in Precambrian seas.
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Figure 17.4
• At the beginning of the Cambrian period, 542
million years ago, animals underwent a rapid
diversification.
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Figure 17.5
• 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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• Three evolutionary branch points have been
hypothesized.
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Figure 17.6
• 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.
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Figure 17.7
• 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.
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Figure 17.8
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.
– Lacks true tissues.
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Figure 17.9
• 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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Figure 17.10
Cnidarians
• Phylum Cnidaria
– Is characterized by the presence of body tissues,
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.
Hydra Budding
Jelly Swimming
Hydra Eating Daphnia
Thimble Jellies
Hydra Releasing Sperm
Coral Reef
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Figure 17.11
• Examples of polyps are
– Hydras, sea anemones, and coral animals.
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Figure 17.12
• Cnidarians are carnivores that use tentacles armed
with cnidocytes, or “stinging cells,” to capture
prey.
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Figure 17.13
Flatworms
• Phylum Platyhelminthes
– Is represented by the simplest bilateral animals.
– Includes free-living forms such as planarians.
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Figure 17.14
• Some flatworms are parasitic.
– Blood flukes are an example.
– Tapeworms parasitize many vertebrates, including
humans.
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Figure 17.15
Roundworms
• Phylum Nematoda
– Includes the most diverse and widespread of all
animals.
– Occurs in aquatic and moist terrestrial habitats.
C. elegans Crawling
C. elegans Embryo Development (time lapse)
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Figure 17.16
• Roundworms exhibit two innovations not found in
flatworms:
– A complete digestive tract with two openings, a
mouth and an anus
– A body cavity, which in this case is a
pseudocoelom
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Annelids
• Phylum Annelida
– Includes worms with body segmentation.
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Figure 17.17
• There are three main classes of annelids:
– Earthworms, which eat their way through soil
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Figure 17.18a
• Polychaetes, which burrow in the sea floor
Tubeworms
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Figure 17.18b
• Leeches, most of which are free-living carnivores
that live in a variety of habitats
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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.
Lobster Mouth Parts
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Figure 17.19
• 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
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Figure 17.20
– Crustaceans, such as crabs, lobsters, crayfish,
shrimps, and barnacles
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Figure 17.21
– Millipedes and centipedes
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Figure 17.22
– Insects, most of which have a three-part body
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Figure 17.23
Figure 17.24
• Many insects undergo metamorphosis in their
development.
Butterfly Emerging
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Figure 17.25
Molluscs
• 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 mollusc has three main parts: a
muscular foot, a visceral mass, and a mantle.
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Figure 17.26
• The three major classes of molluscs are:
– Gastropods, which are protected by a single,
spiraled shell
Nudibranchs
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Figure 17.27a
– Bivalves, protected by shells divided into two
halves
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Figure 17.27b
– Cephalopods, which may or may not have a shell
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Figure 17.27c
Echinoderms
• Phylum Echinodermata
– Is named for the spiny surfaces of the organisms.
– Includes sea stars, sand dollars, sea urchins, and
sea cucumbers.
Echinoderm Tube Feet
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Figure 17.28
• Echinoderms
– Are all marine.
– Are usually sessile or slow moving.
– 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, reptiles,
amphibians, and fishes.
– Have unique features, including the cranium and
backbone.
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Figure 17.29
Characteristics of Chordates
• Members of the phylum Chordata all share four
key features:
– A dorsal, hollow nerve cord
– A notochord
– Pharyngeal slits
– A post-anal tail
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Figure 17.30
• The phylum Chordata is divided into three
subphyla.
– The first two subphyla contain lancelets and
tunicates, invertebrate chordates.
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Figure 17.31
• The third subphylum, vertebrates,
– Retains the basic chordate features but has unique
characteristics.
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• An overview of chordate and vertebrate evolution
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Figure 17.32
Fishes
• The first vertebrates probably evolved during the
early Cambrian period, about 542 million years
ago.
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• These early vertebrates lacked jaws.
– They are represented today by lampreys.
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Figure 17.33a
• The two major groups of living fishes are the
– Chondrichthyans, cartilaginous fishes.
– Osteichthyans, bony fishes.
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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.
Manta Ray
Shark Eating a Seal
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Figure 17.33b
• Bony fishes
– Have a skeleton reinforced by hard calcium salts.
– Have a lateral line system, a keen sense of smell,
and excellent eyesight.
Clownfish and Anemone
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Figure 17.33c
• Most bony fishes are ray-finned fishes.
• A second evolutionary branch of bony fishes
includes lungfishes and lobe-finned fishes.
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Amphibians
• Amphibians
– Exhibit a mixture of aquatic and terrestrial
adaptations.
– Usually need water to reproduce.
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Figure 17.34
• Amphibians
– Were the first vertebrates to colonize land.
– Descended from fishes that had lungs and fins
with muscles.
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Figure 17.35
• Terrestrial vertebrates are collectively called
tetrapods, which means “four feet.”
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Reptiles
• Reptiles (including birds) and mammals are
amniotes,
– Organisms that lay eggs in which the embryo
develops.
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• In addition to laying amniotic eggs,
– Reptiles possess other adaptations for living on
land including waterproof skin.
Snake Ritual Wrestling
Galápagos Tortoise
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Figure 17.36
• Reptiles include
– Snakes, lizards, turtles, crocodiles, and alligators.
• Reptiles are ectotherms.
– They 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.
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Figure 17.37
Birds
• Birds evolved from a lineage of small, two-legged
dinosaurs during the great reptilian radiation of the
Mesozoic era.
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• Almost every element of bird anatomy is modified
for flight:
– Bones that are honeycombed, which makes them
lighter
– The absence of some internal organs, which also
reduces weight
• Physiologically, birds are endotherms,
– Maintaining a warm, constant body temperature,
enhancing metabolic output.
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• A bird’s wings
– Illustrate the same principles of aerodynamics as
the wings of an airplane.
Flapping Geese
Soaring Hawk
Swans Taking Flight
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Figure 17.38
Mammals
• The first true mammals
– Arose about 200 million years ago and were
probably small, nocturnal insect-eaters.
• Most mammals are terrestrial.
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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.
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Figure 17.39a
• 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.
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Figure 17.39b
• 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.
Bat Licking Nectar
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Figure 17.39c
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.
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Figure 17.40
• Taxonomists divide the primates into three main
groups.
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Figure 17.41
• The first group of primates includes lorises, pottos,
and lemurs.
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Figure 17.42a
• Tarsiers form the second group.
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Figure 17.42b
• The third group, anthropoids, includes
– Monkeys
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Figure 17.42c
– Apes, the closest relatives to humans
Chimp Agonistic Behavior
Chimp Cracking Nut
Gibbons Brachiating
Wolves Agonistic Behavior
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Figure 17.42d
– Humans
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Figure 17.42e
The Emergence of Humankind
• Humans and apes have shared a common ancestry
for all but the last 5–7 million years.
• Paleoanthropology
– Is the study of human evolution.
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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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Figure 17.43
• 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.
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Figure 17.44
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 Dispersal 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 and Dispersal of Homo Sapiens
• The oldest known fossils of our own species, H.
sapiens,
– Were discovered in Ethiopia.
– Date from 160,000 to 195,000 years ago.
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• DNA studies indicate that Europeans and Asians
share a recent common ancestor
– And that many African lineages represent earlier
branches on the human tree.
• Mitochondrial DNA and Y chromosome analysis
also support this conclusion.
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• Fossil evidence suggests that our species emerged
from Africa in one or more waves,
– Spreading first into Asia and then to Europe and
Australia.
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Cultural Evolution
• Culture
– Is the social 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.
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Figure 17.45
• 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 20th 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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Figure 17.46