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Title: Evolution

Chapter 7
EvolutionThe Theory and Its Supporting Evidence
Evidence for Evolution
  • Some of the evidence for evolution
  • is provided by fossils
  • such as this Early Pleistocene mammoth
  • known as Archidiskodon meridonalis
  • on display in the Museum of Geology and
    Paleontology at the University of Florence in

Darwin and the Galápagos
  • During Charles Darwins five-year voyage
  • (1831-1836) on the HMS Beagle,
  • he visited the Galápagos Islands
  • where he made important observations
  • that changed his ideas about
  • the then popular concept called the fixity of
  • an idea holding that all present-day species
  • had been created in their present form
  • and had changed little or not at all
  • Darwin fully accepted
  • the Biblical account of creation before the voyage

Route of HMS Beagle
  • Map showing the route (red line) followed
  • by Charles Darwin when he was aboard
  • HMS Beagle from 1831 to 1836
  • The Galápagos Islands
  • are in the Pacific Ocean west of Ecuador

The Galápagos Islands
  • The Galápagos Islands
  • are specks of land
  • composed of basalt
  • in the eastern Pacific

The Galápagos Islands
Darwin Developed the Theory
  • During the voyage Darwin observed
  • that fossil mammals in South America
  • are similar yet different from present-day
  • llamas, sloths, and armadillos
  • that the finches and giant tortoises living
  • on the Galápagos Islands vary from island to
  • and still resemble ones from South America,
  • even though they differ in subtle ways
  • These observations convinced Darwin
  • that organisms descended with modification
  • from ancestors that lived during the past
  • the central claim of the theory of evolution

Galápagos Finches
  • Darwins finches from the Galápagos Islands
  • arranged to show evolutionary relationships
  • Notice that beak shape
  • varies depending on diet

Berry eater
Seed eaters
Cactus eaters
Why Study Evolution?
  • Evolution
  • involving inheritable changes in organisms
    through time
  • is fundamental to biology and paleontology
  • Paleontology is the study of life history as
    revealed by fossils
  • Evolution is a unifying theory
  • like plate tectonic theory
  • that explains an otherwise
  • encyclopedic collection of facts
  • Evolution provides a framework
  • for discussion of life history
  • in later parts of the term

Misconceptions about Evolution
  • Many people have a poor understanding
  • of the theory of evolution
  • and hold a number of misconceptions,
  • which include
  • evolution proceeds strictly by chance
  • nothing less than fully developed structures
  • such as eyes are of any use
  • there are no transitional fossils
  • so-called missing links
  • connecting ancestors and descendants
  • humans evolved from monkeys
  • so monkeys should no longer exist

Evolution Historical Background
  • Evolution, the idea that todays organisms
  • have descended with modification
  • from ancestors that lived during the past,
  • is usually attributed solely to Charles Darwin,
  • but it was seriously considered long before he
    was born,
  • even by some ancient Greeks
  • and by philosophers and theologians
  • during the Middle Ages
  • Nevertheless, the prevailing belief
  • in the 1700s was that Genesis
  • explained the origin of life
  • and contrary views were heresy

Evolution Historical Background
  • During the 18th century,
  • naturalists were discovering evidence
  • that could not be reconciled
  • with literal reading of Scripture
  • In this changing intellectual atmosphere,
  • scientists gradually accepted a number of ideas
  • the principle of uniformitarianism,
  • Earths great age,
  • that many types of plants and animals had become
  • and that change from one species to another
  • What was lacking, though,
  • was a theoretical framework to explain evolution

  • Jean-Baptiste de Lamarck
  • (1744-1829) is best remembered for his theory
  • of inheritance of acquired characteristics,
  • even though he greatly contributed
  • to our understanding of the natural world
  • According to this theory,
  • new traits arise in organisms because of their
  • and are somehow passed on to their descendants
  • Lamarcks theory seemed logical at the time
  • and was widely accepted

Lamarcks Theory
  • Lamarks theory was not totally refuted
  • until decades later
  • with the discovery that genes
  • units of heredity
  • cannot be altered by any effort by an organism

Lamarcks Giraffes
  • According to Lamarcks theory of inheritance of
    acquired characteristics
  • ancestral short-necked giraffes
  • stretched their necks
  • to reach leaves high on trees
  • their offspring were born
  • with longer necks

  • In 1859, Charles Robert Darwin (1809-1882)
  • published On the Origin of Species
  • In it he detailed
  • his ideas on evolution
  • formulated 20 years earlier
  • and proposed a mechanism for evolution

Natural Selection
  • Plant and animal breeders
  • practice artificial selection
  • by selecting those traits they deem desirable
  • and then breed plants and animals with those
  • thereby bringing about a great amount of change
  • Observing artificial selection
  • gave Darwin the idea that
  • a process of selection among variant types
  • in nature could also bring about change
  • Thomas Malthuss essay on population
  • suggested that competition for resources
  • and high infant mortality limited population size

Darwin and Wallace
  • Darwin and Alfred Russel Wallace (1823-1913)
  • read Malthuss book
  • and came to the same conclusion,
  • that a natural process
  • was selecting only a few individuals for survival
  • Darwins and Wallaces idea
  • called natural selection
  • was presented simultaneously in 1859

Natural SelectionMain Points
  • Organisms in all populations
  • posses heritable variations such as
  • size, speed, agility, visual acuity,
  • digestive enzymes, color, and so forth
  • Some variations are more favorable than others
  • some have a competitive edge
  • in acquiring resources and/or avoiding predators
  • Not all young survive to reproductive maturity
  • Those with favorable variations
  • are more likely to survive
  • and pass on their favorable variations

Naturally Selected Giraffes
  • According to the Darwin-Wallace theory
  • of natural selection, giraffes long neck evolved
  • because ancestors with longer necks
  • had an advantage
  • and reproduced more often

Survival of the Fittest
  • In colloquial usage,
  • natural selection is sometimes expressed as
  • survival of the fittest
  • This is misleading because
  • natural selection is not simply a matter of
  • but involves differential rates
  • of survival and reproduction

Not only Biggest, Strongest, Fastest
  • One misconception about natural selection
  • is that among animals
  • only the biggest, strongest, and fastest
  • are likely to survive
  • These characteristics might provide an advantage
  • but natural selection may favor
  • the smallest if resources are limited
  • the most easily concealed
  • those that adapt most readily to a new food
  • those having the ability to detoxify some
  • and so on...

Limits of Natural Selection
  • Natural selection works
  • on existing variation in a population
  • It could not account for the origin of variations
  • Critics reasoned that should a variant trait
  • it would blend with other traits and would be
  • The answer to these criticisms
  • existed even then in the work of Gregor Mendel,
  • but remained obscure until 1900

Mendel and the Birth of Genetics
  • During the 1860s, Gregor Mendel,
  • an Austrian monk,
  • performed a series of controlled experiments
  • with true-breeding strains of garden peas
  • strains that when self-fertilized
  • always display the same trait, such as flower
  • Traits are controlled by a pair of factors,
  • now called genes
  • Genes occur in alternate forms, called alleles
  • One allele may be dominant over another
  • Offspring receive one allele
  • of each pair from each parent

Mendels Experiments
  • The parental generation consisted of
  • true-breeding strains, RR red flowers, rr
    white flowers
  • Cross-fertilization yielded a second generation
  • all with the Rr combination of alleles,
  • in which the R (red) is dominant over r (white)

Mendels Experiments
  • The second generation, when self-fertilized
  • produced a third generation
  • with a ratio of three red-flowered plants
  • to one white-flowered plant

Importance of Mendels Work
  • The factors (genes) controlling traits
  • do not blend during inheritance
  • Traits not expressed in each generation
  • may not be lost
  • Therefore, some variation in populations
  • results from alternate expressions of genes
  • Variation can be maintained

Genes and Chromosomes
  • Complex, double-stranded helical molecules
  • of deoxyribonucleic acid (DNA)
  • called chromosomes
  • are found in cells of all organisms
  • except bacteria,
  • which have ribonucleic acid (RNA)
  • Specific segments of DNA
  • are the basic units of heredity (genes)
  • The number of chromosomes
  • varies from one species to another
  • fruit flies 8 humans 46 horses 64

Sexually Reproducing Organisms
  • In sexually reproducing organisms,
  • the production of sex cells
  • pollen and ovules in plants
  • sperm and eggs in animals
  • results when cells undergo a type of cell
  • known as meiosis
  • This process yields cells
  • with only one chromosome of each pair
  • so all sex cells have
  • only 1/2 the chromosome number
  • of the parent cell

  • During meiosis,
  • sex cells form that contain one member
  • of each chromosome pair
  • Formation of sperm is shown here
  • Eggs form the same way,
  • but only one of the four final eggs
  • is functional

  • The full number of chromosomes
  • is restored when a sperm fertilizes an egg
  • or when pollen fertilizes an ovule
  • The egg (or ovule) then
  • has a full set of chromosomes
  • typical for that species
  • As Mendel deduced,
  • 1/2 the genetic makeup
  • of fertilized egg
  • comes from each parent
  • The fertilized egg
  • grows by mitosis

  • Mitosis is cell division
  • that results in
  • the complete duplication of a cell
  • In this example,
  • a cell with four chromosomes (two pairs)
  • produce two cells
  • each with four chromosomes
  • Mitosis takes place
  • in all cells except sex cells

  • Once an egg
  • has been fertilized,
  • the developing embryo
  • grows by mitosis

Modern View of Evolution
  • During the 1930s and 1940s,
  • paleontologists, population biologists,
  • geneticists, and others developed ideas that
  • merged to form a modern synthesis
  • or neo-Darwinian view of evolution
  • They incorporated
  • chromosome theory of inheritance
  • into evolutionary thinking
  • They saw changes in genes (mutations)
  • as one source of variation

Modern View of Evolution
  • They completely rejected Lamarcks idea
  • of inheritance of acquired characteristics
  • They reaffirmed the importance of natural
  • But since then,
  • some scientists have challenged the emphasis
  • in modern synthesis
  • that evolution is gradual

What Brings about Variation?
  • Evolution by natural selection
  • works on variation in populations
  • most of which is accounted for by the reshuffling
  • of alleles from generation to generation
  • during sexual reproduction
  • The potential for variation is enormous
  • with thousands of genes
  • each with several alleles,
  • and with offspring receiving 1/2 of their genes
  • from each parent
  • New variations arise by mutations
  • change in the chromosomes or genes

  • Mutations result in a change
  • in hereditary information
  • Mutations that take place in sex cells
  • are inheritable,
  • whether they are chromosomal mutations
  • affecting a large segment of a chromosome
  • or point mutations
  • individual changes in particular genes
  • Mutations are random with respect to fitness
  • they may be beneficial, neutral, or harmful

  • If a species is well adapted to its environment,
  • most mutations would not be particularly useful
  • and perhaps would be harmful
  • But what was a harmful mutation
  • can become a useful one
  • if the environment changes

Neutral Mutations
  • Information in cells is carried on chromosomes
  • which direct the formation of proteins
  • by selecting the appropriate amino acids
  • and arranging them into a specific sequence
  • Neutral mutations may occur
  • if the information carried on the chromosome
  • does not change the amino acid or protein
  • that is produced

What Causes Mutations?
  • Some mutations are induced by mutagens
  • agents that bring about higher mutations rates
    such as
  • some chemicals
  • ultraviolet radiation
  • X-rays
  • extreme temperature changes
  • Some mutations are spontaneous
  • occurring without any known mutagen

  • Species is a biological term for a population
  • of similar individuals that in nature interbreed
  • and produce fertile offspring
  • Species are reproductively isolated
  • from one another
  • Goats and sheep do not interbreed in nature,
  • so they are separate species
  • Yet in captivity
  • they can produce fertile offspring

  • Speciation is the phenomenon of a new species
  • arising from an ancestral species
  • It involves change in the genetic makeup
  • of a population,
  • which also may bring about changes
  • in form and structure
  • During allopatric speciation,
  • species arise when a small part of a population
  • becomes isolated from its parent population

Allopatric Speciation
  • Reduction of the area occupied by a species
  • may leave a small isolated population
  • Two peripheral isolates evolved into new species
  • Isolation might result from a marine

Allopatric Speciation
  • Geographic barriers may form across parts
  • of a central populations range,
  • thereby isolating small populations that speciate

Allopatric Speciation
  • A few individuals may somehow reach
  • a remote area and no longer exchange genes
  • with the parent population
  • This out-migration can lead to the formation
  • of a peripheral isolate that gives rise to a new
  • while the parent population persists without

Finch Speciation
  • Darwins finches from the Galápagos Islands
  • underwent allopatric speciation
  • due to isolation of birds among the many islands

Rate of Speciation
  • Although widespread agreement exists
  • on allopatric speciation
  • scientists disagree on how rapidly
  • a new species might evolve
  • Phyletic gradualism
  • the gradual accumulation of minor changes
  • eventually brings about the origin of new species
  • This view was held by Darwin and reaffirmed by
    modern synthesis

Rate of Speciation
  • Punctuated equilibrium
  • holds that little or no change
  • takes place in a species
  • during most of its existence
  • then evolution occurs rapidly
  • giving rise to a new species
  • in perhaps as little as a few thousand years

  • Ideas about speciation
  • commonly involve misconceptions
  • One antievolution argument is
  • If humans evolved from monkeys,
  • why are there still monkeys?
  • This involves two misconceptions
  • No scientist has ever claimed
  • that humans evolved from monkeys
  • Even if they had, that would not preclude
  • the possibility of monkeys still existing

Various Possibilities
  • In allopatric speciation
  • a small population may evolve
  • whereas the larger parent population may
  • remain unchanged,
  • evolve in some other direction,
  • or become extinct

Styles of Evolution
  • Divergent evolution occurs
  • when an ancestral species
  • giving rise to diverse descendants
  • adapts to various aspects of the environment
  • Divergent evolution leads to descendants
  • that differ markedly from their ancestors
  • Convergent evolution involves the development
  • of similar characteristics
  • in distantly related organisms
  • Parallel evolution involves the development
  • of similar characteristics
  • in closely related organisms

Styles of Evolution
  • In both convergent and parallel evolution,
  • similar characteristics developed independently
  • in comparable environments

Divergent Evolution
  • Divergent evolution of a variety
  • of placental mammals from a common ancestor
  • Divergence accounts for descendants
  • that differ from their ancestors and from one

Convergent Evolution
  • Convergent evolution takes place
  • when distantly related organisms give rise to
  • that resemble one another
  • because they adapt
  • in comparable ways

Parallel Evolution
  • Parallel evolution
  • involves the independent origin
  • of similar feature in related organisms

Cladistics and Cladograms
  • Traditionally, scientists have
  • depicted evolutionary relationships
  • with phylogenetic trees
  • in which the horizontal axis represents
  • anatomical differences
  • and the vertical axis denotes time
  • In contrast, a cladogram shows
  • the relationships among members of a clade
  • a group of organisms
  • including its most recent common ancestor
  • Cladistics focus on derived characteristics
  • sometimes called evolutionary novelties
  • as opposed to primitive characteristics

Phylogenetic Tree
  • A phylogenetic tree
  • showing the relationships
  • among various vertebrate animals

  • A cladogram showing inferred relationships
  • Some of the characteristics used
  • to construct this cladogram are indicated

Evolutionary Novelties
  • All land-dwelling vertebrate animals
  • posses bone and paired limbs
  • so these characteristics are primitive
  • and of little use in establishing relationships
  • among land vertebrates
  • However, hair and mammary glands
  • are derived characteristics
  • Only one subclade, the mammals, has them

Evolutionary Novelties
  • If considering only mammals,
  • hair and mammary glands
  • are primitive characteristics,
  • but live birth is a derived characteristic
  • that serves to distinguish most mammals
  • from the egg-laying mammals

  • Three different interpretations
  • of the relationships among
  • bats, dogs and birds

  • Bats and birds fly,
  • which might suggest
  • a closer relationship
  • than to dogs
  • Dogs and birds
  • do not appear closely related
  • Hair and giving birth to live young
  • indicate that bats and dogs
  • are more closely related

Cladistics for Fossils
  • Cladistics and cladograms work
  • well for living organisms,
  • but are trickier for fossils
  • Care must be taken in determining
  • what are primitive verses derived
  • especially in groups with poor fossil records
  • Paleontologists must be especially careful
  • of characteristics resulting
  • from convergent evolution

Cladistics for Fossils
  • Nevertheless, cladistics is a powerful tool
  • that has more clearly elucidated
  • the relationships among many fossil lineages,
  • and is now used extensively by paleontologists

Evolutionary Trends
  • During evolution, all aspects of an organism
  • do not change simultaneously
  • A key feature we associate
  • with a descendant group might appear
  • before other features typical of that group
  • For example, the oldest known bird
  • had feathers and the typical fused clavicles of
  • but it also retained many reptile characteristics
  • Mosaic evolution is the concept that
  • organisms possess recently evolved
  • as well as some features of their ancestral group

  • Phylogeny is the evolutionary history
  • of a group of organisms
  • If sufficient fossil material is available,
  • paleontologists determine the phylogeny
  • and evolutionary trends for groups of organisms
  • For example, one trend in ammonoids
  • extinct relatives of squid and octopus
  • was the evolution
  • of an increasingly complex shell

Evolutionary Trends
  • Abundant fossils show the evolutionary trends of
  • the Eocene mammals family Brontotheridea,
  • better known as titanotheres
  • These extinct relative of horses and rhinoceroses
  • evolved from small ancestors
  • to giants standing 2.4 m at the shoulder
  • developed large horns
  • and the shape of their skull changed
  • Only 4 of the 16 known genera are show

Evolutionary Trends
  • Size increase is
  • one of the most common evolutionary trends
  • However, trends are complex
  • they might reverse
  • more than one can take place
  • at the same time at different rates
  • Trends in horses included
  • generally larger size
  • but size decreased in some now-extinct horses
  • changes in teeth and skull
  • lengthening legs
  • reduction in number of toes
  • These trends occurred at different rates

  • Evolutionary trends are a series of adaptations
  • to changing environment
  • or in response to exploitation of new habitats
  • Some organisms
  • show little evolutionary change
  • for long periods
  • Lingula is a brachiopod
  • with a shell, at least,
  • that has not changed
  • significantly since the Ordovician

Living Fossils
  • Several organisms have shown
  • little or no change for long periods
  • If these still exist as living organisms today
  • they are sometimes called living fossils
  • For example
  • horseshoe crabs
  • closest living relative of a trilobite
  • coelacanth (fish)
  • gingkoes (tree)
  • The absence of change for these organisms
  • is not yet fully understood

A Living Fossil
  • Latimeria
  • belongs to a group of fish
  • once thought to have gone extinct
  • at the end of the Mesozoic Era
  • A specimen was caught
  • off the coast of East Africa in 1938

A Second Living Fossil
  • Ginkgos
  • have changed very little
  • for millions of years
  • They were found
  • living in some isolated habitats in Asia
  • and have been transplanted elsewhere

Randomness in Natural Selection?
  • But isnt evolution by natural selection
  • a random process?
  • If so, how is it possible
  • for a trend to continue long enough
  • to account just by chance
  • for such complex structures as
  • eyes, wings, and hands?

Two Steps in Natural Selection
  • Evolution by natural selection
  • is a 2 step process
  • Only the first step involves chance
  • Variation must be present
  • or arise in a population
  • Whether a mutation is favorable
  • is a matter of chance
  • The natural selection of favorable variations
  • is not by chance

  • Perhaps as many as 99 of all species
  • that ever existed are now extinct
  • Organisms do not always evolve
  • toward some kind of higher order of perfection
  • or greater complexity
  • Vertebrates are more complex
  • but not necessarily superior
  • in some survival sense than bacteria
  • after all, bacteria have persisted
  • for at least 3.5 billion years
  • Natural selection yields organisms adapted
  • to a specific set of circumstances
  • at a particular time

Background and Mass Extinction
  • The continual extinction of species
  • is referred to as background extinction
  • It is clearly different from mass extinction
  • during which accelerated extinction rates
  • sharply reduce Earths biotic diversity
  • Extinction is a continual occurrence
  • but so is the evolution of new species
  • that usually quickly exploit the opportunities
  • another species extinction creates
  • Mammals began a remarkable diversification
  • when they began occupying niches
  • the extinction of dinosaurs and their relatives
    left vacant

Mass Extinction
  • The mass extinction of dinosaurs
  • and other animals at the end of Mesozoic Era
  • is well known,
  • but the greatest mass extinction
  • occurred at the end of the Paleozoic Era
  • More than 90 of all species died out
  • We will discuss these extinctions
  • and their possible causes later in the term

Evidence in Support of Evolution
  • Darwin cited supporting evidence
  • for evolutionary theory such as
  • classification
  • embryology
  • comparative anatomy
  • geographic distribution
  • fossil record, to a limited extent
  • He had little knowledge
  • of the mechanism of inheritance
  • and biochemistry and molecular biology
  • were unknown at his time

Evidence in Support of Evolution
  • Since Darwins time, studies from additional
  • in biochemistry
  • molecular biology
  • more complete and better understood fossil record
  • have convinced scientists that the theory
  • is as well supported by evidence
  • as any other major theory
  • Scientists still disagree on many details,
  • but the central claim of the theory
  • is well established and widely accepted

Is the Theory of Evolution Scientific?
  • An idea can only be a truly scientific theory
  • if testable predictive statements
  • can be made from it
  • No theory in science is ever proven
  • in the final sense,
  • although substantial evidence may support it
  • All theories are always open
  • to question, revision and occasionally
  • to replacement by a more comprehensive theory

Theories Must Be Predictive
  • By predictive, we do not mean that
  • it can predict the future
  • No one knows which existing species
  • will become extinct, or what descendants
  • of any particular organism, if any,
  • will look like in 10 million years from now
  • Nevertheless, we can make a number of predictions
  • about the present-day biological world
  • and about the fossil record
  • that should be consistent with the theory of
  • if it is correct

Some Predictions from Evolution
  • If evolution has taken place,
  • the oldest fossil-bearing rocks should have
  • very different fossils than organisms of today
  • More recent rocks should have
  • more fossils similar to todays organisms
  • Closely related species should have similarities
  • in a whole range of areas, not just anatomy

Some Predictions from Evolution
  • Classification of organisms
  • should show a nested pattern of similarities
  • Neighboring plants and animals
  • should be more similar to each other
  • than to ones farther away
  • A mechanism should exist
  • that allows the evolution of one species to
  • fossils should appear in the fossil record
  • in order of the organisms evolution

  • Suppose that contrary to evolutionary prediction
  • wolves and coyotes were not similar
  • in terms of their biochemistry, genetics
  • and embryonic development
  • Our prediction would fail
  • and we would at least have to modify the theory
  • If other predictions also failed
  • say, if mammals appeared in the fossil record
    before fishes
  • then we would have to abandon the theory
  • and find a better explanation for our
  • Since the theory of evolution is testable,
  • it is truly scientific

  • Classification uses a nested pattern of
  • Carolus Linneaus (1707-1778) proposed
  • a classification scheme
  • in which organisms receive a two-part name
  • consisting of genus and species
  • for example, the coyote is Canis latrans
  • Linnaeuss classification is an ordered list
  • of categories that becomes more inclusive
  • as one proceeds up the hierarchy

Linnaean Classification
  • the coyote, Canis latrans
  • Animalia
  • Chordata
  • Vertebrata
  • Mammalia
  • Carnivora
  • Most inclusive
  • Kingdom
  • Phylum
  • Subphylum
  • Class
  • Order
  • Canidae
  • Canis
  • latrans
  • Family
  • Genus
  • Species

Least inclusive
Classification shared Characteristics
  • Subphylum vertebrata
  • including fishes, amphibians, reptiles, birds and
  • have a segmented vertebral column
  • Only warm-blooded animals with hair/fur and
    mammary glands are mammals

Coyote, Canis latrans
  • 18 orders of mammals exist including order
  • The Family Canidae are doglike carnivores
  • and the genus Canis includes only closely related
  • Coyote, Canis latrans, stands alone as a species

Coyote and Wolf
  • Coyote (Canis latrans) and wolf (Canis lupus)
  • share numerous characteristics
  • as members of the same genus
  • They share some but fewer characteristics
  • with the red fox (Volpes fulva)
  • in the family Canidae
  • All canids share some characteristics with cats,
  • bears and weasels in the order Carnivora
  • which is one of 18 living orders
  • of the class Mammalia
  • Shared characteristics
  • are evidence for evolutionary relationships

Biological Evidence Supporting Evolution
  • If all existing organisms actually evolved
  • from ancestors that lived during the past,
  • all life forms should have fundamental
  • all living things consist mainly of carbon,
    nitrogen hydrogen and oxygen
  • their chromosomes consist of DNA
  • except bacteria which have RNA
  • all cells synthesize proteins
  • in essentially the same way

Evolutionary Relationships
  • Biochemistry provides evidence
  • for evolutionary relationships
  • Blood chemistry is similar among all mammals
  • Humans blood chemistry is related
  • most closely to the great apes
  • then to Old World monkeys
  • then New World monkeys
  • then lower primates such as lemurs
  • Biochemical test support the idea
  • that birds descended from reptiles
  • a relationship also evidenced in the fossil record

Structures with Similarities
  • Homologous structures
  • are basically similar structures
  • that have been modified for different functions
  • They indicate derivation from a common ancestor.
  • Analogous structures are structures
  • with similarities unrelated
  • to evolutionary relationships
  • that serve the same function
  • but are quite dissimilar
  • in both structure and development

Homologous Structures
  • Forelimbs of humans, whales, dogs, and birds
  • are superficially dissimilar,
  • yet all are made up of the same bones,
  • have similar arrangement
  • of muscles, nerves and blood vessels,
  • are similarlyarranged with respect to other
  • have similar pattern of embryonic development

Analogous Structures
  • Wings of insects, birds and bats
  • serve the same function but differ considerably
  • in structure and embryological development
  • Are any of these wings
  • both analogous and homologous?
  • Yes, bird and bat wings

Vestigial Structures
  • Vestigial structures are nonfunctional remnants
  • of structures in organisms that were functional
  • in their ancestors
  • Why do dogs have tiny,
  • functionless toes on their feet (dewclaws)?
  • Ancestral dogs had five toes
  • on each foot,
  • all of which contacted the ground
  • As they evolved
  • they became toe-walkers with only four toes on
    the ground
  • and the big toes and thumbs were lost or reduced
  • to their present state

Remnants of Toes in Horses
  • Normally a horses back foot
  • has only one functional toe,
  • the third
  • Splints are small
  • remnants of toes 2 and 4
  • that remain as vestiges
  • Occasionally,
  • horses are born
  • with one or both
  • of these vestiges enlarged

Evolution in Living Organisms
  • Small-scale evolution can be observed today.
  • For example
  • adaptations of some plants to contaminated soils
  • insects and rodents developing resistance to new
    insecticides and pesticides
  • development of antibiotic-resistant strains of
  • Variations in these populations
  • allowed some variant types
  • to live and reproduce,
  • bringing about a genetic change

What do We Learn from Fossils?
  • The fossil record consists
  • of first appearances of various organisms
  • through time
  • One-celled organisms appeared
  • before multicelled ones
  • plants appeared before animals
  • invertebrates before vertebrates
  • Fish appeared first followed
  • in succession by amphibians,
  • reptiles, mammals, and birds

Advent of Various Vertebrates
  • Times when major groups of vertebrates appeared
    in the fossil record
  • Thickness of spindles shows relative abundance

Fossils Are Common
  • Fossils are much more common
  • than many people realize
  • However the origin and initial diversification
  • of a group is generally the most poorly
  • But fossils showing the diversification
  • of horses, rhinoceroses, and tapirs
  • from a common ancestor are known
  • as are ones showing the origin
  • of birds from reptiles
  • and the evolution
  • of whales from a land-dwelling ancestor

Horses and Their Relatives
  • This cladogram shows the relationship among
  • tapirs, rhinoceroses, horses and their extinct
  • the titanotheres and chalicothers
  • which are well documented by fossils

Horses and Their Relatives
  • These might seem an odd assortment of animals
  • but fossils and studies of living animals
  • indicate that they shared a common ancestor
  • As we trace these animals back
  • in the fossil record,
  • differentiating one from the other
  • becomes increasingly difficult
  • The earliest members of each group
  • are remarkably similar,
  • differing mostly in size and details of their
  • As their diversification proceeded
  • the differences became more apparent

Never Enough
  • Of course, we will never have enough fossils
  • to document the evolutionary history
  • of all living creatures simply because
  • is an incomplete process
  • The remains of some organisms
  • are more likely to be preserved than those of
  • and accumulation of sediments
  • varies in both space and time
  • But several other kinds of evidence
  • support the concept of evolution
  • including biochemistry, comparative anatomy,
  • genetics, molecular biology,
  • and small-scale evolution of living organisms

  • Jean Baptiste de Lamarck proposed
  • the first formal theory of evolution
  • to be taken seriously
  • Inheritance of acquired characteristics
  • was his mechanism for evolution
  • In 1859 Charles Robert Darwin
  • and Alfred Russel Wallace
  • published their views on evolution,
  • and proposed natural selection
  • as the mechanism for evolutionary change

  • Gregor Mendels breeding experiments
  • with garden peas provided some of the answers
  • regarding how variation
  • is maintained and passed on
  • Mendels work is the basis for modern genetics
  • Genes are the hereditary determinants
  • in all organisms
  • This genetic information is carried
  • in the chromosomes of cells
  • Only the genes in
  • the chromosomes of sex cells are inheritable

  • Sexual reproduction and mutations
  • account for most variation in populations
  • Evolution by natural selection has 2-steps
  • First, variation must be produced
  • and maintained in interbreeding populations,
  • and second, favorable variants
  • must be selected for survival
  • An important way by which new species evolve
  • is allopathic speciation

  • When a group is isolated
  • from its parent population,
  • gene flow is restricted or eliminated,
  • and the isolated group is subjected
  • to different selection pressures
  • Divergent evolution involves
  • an ancestral stock giving rise
  • to diverse species
  • The development of similar adaptive types
  • in different groups of organisms results
  • from parallel and convergent evolution

  • Scientists are increasingly using
  • cladistic analyses to determine relationships
  • among organism,
  • but they still show relationships
  • using phylogenetic trees
  • Extinctions take place continually,
  • and times of mass extinctions
  • resulting in marked decreases
  • in Earths biologic diversity
  • have occurred several times

  • The theory of evolution is truly scientific
  • because we can make observations
  • that would falsify it
  • That is, it could conceivably be proved wrong
  • Much of the evidence supporting
  • the theory of evolution comes from
  • classification, embryology, genetics,
  • biochemistry, molecular biology,
  • and present-day small-scale evolution

  • The fossil record also provides evidence
  • for evolution in that it shows a sequence
  • of different groups appearing through time,
  • and some fossils show features
  • we would expect in the ancestors of birds
  • or mammals, and so on
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