Evolution—The Theory and Its Supporting
Evidence
-ideas change thru time: Lamarck to Darwin to Mendel…..
-voyage of HMS Beagle: Galapagos Islands…finches….
allopatric speciation- isolation of populations
-phyletic gradualism vs punctuated equilibrium
-Evolution- an explanation that ties disparate events together…
‘survival of the fittest’….bit of a misnomer…
-’Living fossils’ today: coelocanth and ginkgo
-Mass extinctions ….in geologic past
-Structure and function of limbs: homologous, analogous, and vestigial
-The Linnean biological classification: ….species…genus…

• 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
Italy

• The fossil record consists
– of first appearances of various organisms
– through time
• One-celled organisms appeared
– before multi-celled ones
– plants appeared before animals
– invertebrates before vertebrates
• Fish appeared first followed
– in succession by amphibians,
– reptiles, mammals, and birds

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

• Fossils are much more common
– than many people realize
• However the origin and initial diversification
– of a group is generally the most poorly represented
• 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

• During Charles Darwin’s 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 species
• 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

• 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
– are specks of land
– composed of basalt
– in the eastern Pacific

• 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 island
– 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

• 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

• 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, the idea that today’s 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

• During the 18 th 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,
• Earth’s great age,
• that many types of plants and animals had become extinct,
• and that change from one species to another occurred
• 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 needs
– and are somehow passed on to their descendants
• Lamarck’s theory seemed logical at the time
– and was widely accepted

• Lamark’s 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

• According to Lamarck’s 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

• Plant and animal breeders
– practice artificial selection
– by selecting those traits they deem desirable
– and then breed plants and animals with those traits
– 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 Malthus’s essay on population
– suggested that competition for resources
– and high infant mortality limited population size

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

• Organisms in all populations
– possess 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

• According to the Darwin-Wallace theory
– of natural selection, giraffe’s long neck evolved
– because ancestors with longer necks
– had an advantage
– and reproduced more often

• 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 survival
– but involves differential rates
– of survival and reproduction

• 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 source
– those having the ability to detoxify some substance
– and so on...

• 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 arise,
– it would blend with other traits and would be lost
• The answer to these criticisms
– existed even then in the work of Gregor Mendel ,
– but remained obscure until 1900

• 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
• 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

• 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

• 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 transgression.

• Geographic barriers may form across parts
– of a central population’s range,
– thereby isolating small populations that speciate

• Darwin’s finches from the Galápagos Islands
– underwent allopatric speciation
– due to isolation of birds among the many islands
Berry eater
Cactus eaters
Insect eaters
Seed eaters

• 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 color
• 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

• 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)

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

• 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 (alleles)
• Variation can be maintained

• 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

• 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 division
– 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

• 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

• 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

• 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

•
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

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

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

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

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

•
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

• 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

• 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

• 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

•
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

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

• 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

• 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 Earth’s 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

• 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

• 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

• Since Darwin’s time, studies from additional fields
– 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

• 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

• 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 evolution,
– if it is correct

• 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 today’s organisms
• Closely related species should have similarities
– in a whole range of areas, not just anatomy

• 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 another
– 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 observations
• Since the theory of evolution is testable,
– it is truly scientific

• If all existing organisms actually evolved
– from ancestors that lived during the past,
• all life forms should have fundamental similarities:
– 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

• 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

• 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

• 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 similarly arranged with respect to other structures,
– have similar pattern of embryonic development

• 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 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

• Classification uses a nested pattern of similarities
• 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
• Linnaeus’s classification is an ordered list
– of categories that becomes more inclusive
– as one proceeds up the hierarchy

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

• Subphylum vertebrata
– including fishes, amphibians, reptiles, birds and mammals,
– have a segmented vertebral column
• Only warmblooded animals with hair/fur and mammary glands are mammals

• 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

• 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 bacteria
• Variations in these populations
– allowed some variant types
– to live and reproduce,
– bringing about a genetic change

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

• 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 teeth
• As their diversification proceeded
– the differences became more apparent

• Of course, we will never have enough fossils
– to document the evolutionary history
– of all living creatures simply because fossilization
– is an incomplete process
• The remains of some organisms
– are more likely to be preserved than those of others
– 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 Mendel’s breeding experiments
– with garden peas provided some of the answers
– regarding how variation
– is maintained and passed on
– Mendel’s 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 Earth’s 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

• 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

• 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 birds,
– but it also retained many reptile characteristics
• Mosaic evolution is the concept that
– organisms possess recently evolved characteristics
– as well as some features of their ancestral group

• Normally a horse’s 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

• 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

• A phylogenetic tree
– showing the relationships
– among various vertebrate animals

• 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

• 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

• Darwin’s finches from the Galápagos Islands
– arranged to show evolutionary relationships
Insect eaters
Berry eater
Seed eaters
Cactus eaters
Insect eaters
– Notice that beak shape
– varies depending on diet

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

• In both convergent and parallel evolution,
– similar characteristics developed independently
– in comparable environments

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

• 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

• 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 species
– while the parent population persists without change

• Ideas about speciation
– commonly involve misconceptions
• One anti-evolution 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

• They completely rejected Lamarck’s idea
– of inheritance of acquired characteristics
• They reaffirmed the importance of natural selection
• But since then,
– some scientists have challenged the emphasis
– in modern synthesis
– that evolution is gradual

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

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

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

• But isn’t 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?

• 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

• 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