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Chapter 14

Macroevolution

Macroevolution and theDiversity of Life

– Microevolution• A generation-to-generation change in a

population’s frequencies of alleles.

– Macroevolution• Major changes in the history of life (fossil record)• Formation of new species which generates

biological diversity.

– The formation of new species: Speciation• In nonbranching evolution, a population

transforms but does not create a new species.• In branching evolution, one or more new

species branch from a parent species that maycontinue to exist.

What Is a Species?– Species is a Latin word meaning “kind” or

“appearance.”– The biological species concept defines a

species as• A population or group of populations whose

members have the potential to interbreed andproduce fertile offspring.

– The biological species concept cannot beapplied in all situations, for example, withfossils and asexual organisms.

Important exceptions:Reproductive

BarriersbetweenSpecies

– Prezygoticbarriers preventmating betweenspecies.

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– Examples of behavioral isolation:

Blue-Footed Boobies Courtship Ritual

Giraffe Courtship Ritual

Albatross Courtship Ritual

ReproductiveBarriersbetweenSpecies

– Postzygoticbarriers• Are mechanisms

that operateshouldinterspeciesmating actuallyoccur and formhybrid zygotes.

– Postzygotic barriers include• Hybrid inviability.• Hybrid sterility.

Mechanisms of Speciation

– A key event in the potential origin of aspecies occurs when a population issomehow severed from other populationsof the parent species.

– The two modes of speciation are• Allopatric speciation.• Sympatric speciation.

Allopatric Speciation– Geologic processes

• Can fragment a population into two or moreisolated populations.

• Can contribute to allopatric speciation.

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– Speciation occurs only with the evolution ofreproductive barriers between the isolatedpopulation and its parent population.

Sympatric Speciation– Sympatric speciation occurs if a genetic

change produces a reproductive barrierbetween mutants and the parentpopulation.

Polyploidy, amechanism ofsympatric speciation,was first observed byHugo de Vries.

– Polyploids• Can originate from

accidents duringmeiosis(nondisjunction).

• Can result from thehybridization of twoparent species.

– Many domesticatedplants are the resultof sympatricspeciation.

How Accidents During MeiosisCan Alter Chromosome Number

– In nondisjunction,• The members of a chromosome pair fail to separate

during anaphase.• Gametes with an incorrect number of chromosomes

are produced.

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Figure 8.20

– The result of nondisjunction

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Down Syndrome: An ExtraChromosome 21

– Down Syndrome• Is a condition where an individual has an extra

chromosome 21.• Is also called trisomy 21.

– Polyploids• Can originate from

accidents duringmeiosis(nondisjunction).

• Can result from thehybridization of twoparent species.

– Many domesticatedplants are the resultof sympatricspeciation.

What Is the Tempo ofSpeciation?

– Traditional evolutionary trees diagram thedescent of species as gradual divergence.

– Punctuated equilibrium• Is a contrasting model of evolution.• States that species most often diverge in spurts of

relatively sudden change.• Accounts for the relative rarity of transitional fossils.

The Evolution of BiologicalNovelty

– What accounts for the evolution ofbiological novelty?

Adaptation of Old Structuresfor New Functions

– Birds• Are derived from a lineage of earthbound

reptiles.• Developed from flightless ancestors, but how?

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– An exaptation:• Is a structure that evolves in one context, but

becomes adapted for another function

• Is a type of evolutionary remodeling

– Exaptations can account for the gradualevolution of novel structures.

– Bird wings are modified forelimbs that werepreviously adapted for non-flight functions, suchas:• Thermal regulation• Courtship displays• Camouflage

– The first flights may have been only glides orextended hops as the animal pursued prey orfled from a predator.

Evo-Devo: Development andEvolutionary Novelty

– A subtle change in a species’ developmentalprogram can have profound effects, changingthe:• Rate• Timing• Spatial pattern of development

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– Evo-devo, evolutionary developmental biology,is the study of the evolution of developmentalprocesses in multicellular organisms.

– Homeotic genes are master control genes thatregulate:• When structures develop• How structures develop• Where structures develop

– Mutations in homeotic genes can profoundlyaffect body form.

– Watch PBS movie “What Darwin Never Knew”

Earth History andMacroevolution

– Macroevolution• Major changes in the history of life (fossil

record)• Formation of new species which generates

biological diversity.

• Is closely tied to the history of the Earth.

Geologic Time and the FossilRecord

– The fossil record• Is an archive of macroevolution.

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– Geologistshaveestablished ageologic timescalereflecting aconsistentsequence ofgeologicperiods.

– pg 281 in yourtext

– Radiometric dating• Is the most common

method for datingfossils.

• Has helpedestablish thegeologic time scale.

Plate Tectonics andMacroevolution

– The continents are not lockedin place.• They drift about Earth’s surface

on plates of crust floating on aflexible layer called the mantle.

– California’s infamous SanAndreas fault• Is at a border where two plates

slide past each other.

– About 250 millionyears ago

• Plate movementsformed thesupercontinentPangaea.

• Many extinctionsoccurred, allowingsurvivors to diversify.

– About 180 millionyears ago

• Pangaea began tobreak up, causinggeographic isolation.

Mass Extinctions and ExplosiveDiversifications of Life

– The fossil record reveals an episodichistory,• With long, relatively stable periods punctuated

by briefer intervals when the turnover inspecies composition was much more extensive.

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– Extinction is inevitable in a changing world andoccurs all the time.• However, extinction rates have not been steady.

– Extinctions typically eliminate various species oforganisms• And are followed by explosive diversifications of

organisms.

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The Process of Science:Did a Meteor Kill the Dinosaurs?

– Scientists believethat about 65million years ago,at the end of theCretaceousperiod,• A meteor impact

contributed to theextinction of thedinosaurs.

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

CLASSIFYING THE DIVERSITYOF LIFE

– Systematics focuses on:• Classifying organisms• Determining their evolutionary relationships

– Taxonomy is the:• Identification of species• Naming of species• Classification of species

Some Basics of Taxonomy– Scientific names ease communication by:

• Unambiguously identifying organisms• Making it easier to recognize the discovery of a new species

– Carolus Linnaeus (1707–1778) proposed the currenttaxonomic system based upon:

• A two-part name for each species• A hierarchical classification of species into broader groups of

organisms

Naming Species

– Each species is assigned a two-part name or binomial,consisting of:

• The genus• A name unique for each species

– The scientific name for humans is Homo sapiens, a twopart name, italicized and latinized, and with the first letterof the genus capitalized.

Hierarchical Classification– Species that are closely related are placed into the same

genus.

Jaguar (Panthera onca)

Lion (Panthera leo)Tiger (Panthera tigris)

Leopard (Panthera pardus)

– The taxonomic hierarchy extends toprogressively broader categories of classification

Leopard (Panthera pardus)

SpeciesPantherapardus

GenusPanthera

FamilyFelidae

OrderCarnivora

ClassMammalia

PhylumChordata

KingdomAnimalia

DomainEukarya

Dumb Kids PlayChess On FullGuy’s Stomach

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Classification and Phylogeny– The goal of systematics is to reflect evolutionary

relationships.– Biologists use phylogenetic trees to:

• Depict hypotheses about the evolutionary history of species• Reflect the hierarchical classification of groups nested within

more inclusive groups

Panthera pardus

(leopard)

SpeciesGenus

Felidae

Order

Carnivora

Family

Canis

Lutra

Panthera

Mephitis

Canidae

Mustelidae

Canis lupus(wolf)

Canis latrans

(coyote)

Lutralutra

(Europeanotter)

Mephitis mephitis

(striped skunk)

Figure 14.21

Sorting Homology from Analogy

– Homologous structures:• Reflect variations of a common ancestral plan• Are the best sources of information used to

– Develop phylogenetic trees– Classify organisms according to their evolutionary history

– Analogous Structures emerge throughConvergent evolution:• Involves superficially similar structures in unrelated

organisms• Is based on natural selection

– Similarity due to convergence:• Is called analogy, not homology• Can obscure homologies

Molecular Biology as a Tool inSystematics

– Molecular systematics:• Compares DNA and amino acid sequences between organisms• Can reveal evolutionary relationships

– Some fossils are preserved in such a way that DNAfragments can be extracted for comparison with livingorganisms.

The Cladistic Revolution– Cladistics is the scientific search for clades.– A clade:

• Consists of an ancestral species and all itsdescendants

• Forms a distinct branch in the tree of life

– This is what Neil Shubin did in our readingselection from his book “Your Inner Fish” (2009).

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Human Family Treefrom Shubin’s “Your Inner Fish” (2009)

Cladistics in action

Hair, mammaryglands

Long gestation

Gestation

Duck-billedplatypus

Iguana Outgroup(reptile)

Ingroup(mammals)

Beaver

Kangaroo

Figure 14.23

– Cladistics has changed the traditionalclassification of some organisms

Lizardsand snakes

Crocodilians

Saurischiandinosaurs

Ornithischiandinosaurs

Pterosaurs

Birds

Commonancestor ofcrocodilians,dinosaurs,and birds

Classification: A Work inProgress

– Linnaeus:• Divided all known forms of life between the plant and animal

kingdoms• Prevailed with his two-kingdom system for over 200 years

– In the mid-1900s, the two-kingdom system was replacedby a five-kingdom system that:

• Placed all prokaryotes in one kingdom• Divided the eukaryotes among four other kingdoms

– In the late 20th century, molecular studies and cladisticsled to the development of a three-domain system

KingdomAnimalia

Domain Archaea Earliest organisms

Domain Bacteria

Domain EukaryaKingdomFungi

KingdomPlantae

The protists(multiplekingdoms)

Evolution Connection:Rise of the Mammals

– Mass extinctions:• Have repeatedly occurred throughout Earth’s history• Were followed by a period of great evolutionary change

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– Fossil evidence indicates that:• Mammals first appeared about 180 million years ago• The number of mammalian species

– Remained steady and low in number until about 65 millionyears ago and then

– Greatly increased after most of the dinosaurs becameextinct

American black bear

Eutherians (5,010 species)

Millions of years ago

Monotremes (5 species)

Marsupials (324 species)

Ancestral mammal

Reptilian ancestor

Extinction of dinosaurs

250 200 150 100 5065 0

Figure 14.26