charales darvin

7/28/2019 charales darvin

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During Charles Darwins five-year voyage

(1831-1836) on the HMS Beagle,

he visited the Galpagos Islands

where he made important observations

that changed his ideas aboutthe then popular concept called the f ixity 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

CharlesDarwin


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During the voyage Darwin observedthat fossil mammals in South America

are similar yet different from present-day

llamas, sloths, and armadillos

that the finches and giant tortoises livingon the Galpagos Islands vary from island to island

and still resemble ones from South America,

even though they differ in subtle ways

These observations convinced Darwinthat organisms descended with modification

from ancestors that lived during the past

the central claim of the theory of evolution

Darwin Developed the Theory


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Darwins finches from the Galpagos Islands

arranged to show evolutionary relationships

Galpagos Finches

Noticethat beak

shapevaries

dependingon diet

Berryeater

Insect eaters

Insect eaters

Cactuseaters

Seedeaters


5/100

Evolutioninvolving inheritable changes in organisms through

time

is fundamental to biology and paleontologyPaleontology 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 frameworkfor discussion of life history

Study Evolution


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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

Misconceptions about Evolution


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In 1859, CharlesRobert Darwin (1809-1882)

published On the

Origin of Species in which he detailed

his ideas on evolution

formulated 20 yearsearlier

and proposed amechanism forevolution

Darwin


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Plant and animal breeders

practice artificial selectionby 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 selectiongave Darwin the idea that

a process of selection among variant types

in nature could also bring about change

Thomas Malthus essay on populationsuggested that competition for resources

and high infant mortality limited population size

Natural Selection


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Darwin and Alfred Russel Wallace (1823-1913)

read Malthus 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

Darwin and Wallace


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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 otherssome have a competitive edge

in acquiring resources and/or avoiding predators

Not all young survive to reproductive maturityThose with favorable variations

are more likely to survive

and pass on their favorable variations

Natural SelectionMain Points


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According to the Darwin-Wallace theory

of natural selection, giraffes long neck evolved

Naturally Selected Giraffes

because

ancestorswith longernecks

had an

advantageand

reproducedmore often


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In colloquial usage,natural selection is sometimes expressed as

survival of the fittest

This is misleading becausenatural selection is not simply a matter of survival

but involves differential rates

of survival andreproduction

Survival of the Fittest


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One misconception about natural selectionis that among animals

only the biggest, strongest, and fastest

are likely to surviveThese characteristics might provide an advantage

but natural selection may favorthe 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...

Not only Biggest,

Strongest, Fastest


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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

Limits of Natural Selection


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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 allelesOne allele may be dominant over another

Offspring receive one allele

of each pair from each parent

Mendel and the Birth of Genetics


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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


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The second generation, when self-fertilized

produced a third generation

with a ratio of three red-flowered plants

to one white-flowered plant

Mendels Experiments


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The factors (genes) controlling traits

do not blend during inheritance

Traits not expressed in each generation

may not be lost

Therefore, some variation in populationsresults from alternate expressions of genes (alleles)

Variation can be maintained

Importance of Mendels Work


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called chromosomes

are found in cells of organisms

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

Genes and Chromosomes

Complex, double-stranded

helical moleculesofdeoxyribonucleic acid (DNA)


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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 divisionknown 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

Sexually Reproducing Organisms


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During meiosis,

sex cells form thatcontain one member

of each chromosome

pair Formation of sperm

is shown here

Eggs form the sameway,but only one of the

four final eggs

is functional

Meiosis


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The full number of chromosomes

is restored when a sperm fertilizes an egg

Fertilization

or when pollen fertilizes anovule

The egg (or ovule) then

has a full set ofchromosomestypical for that species

As Mendel deduced,

1/2 the genetic makeupof fertilized eggcomes from each parent

The fertilized egg

grows by mitosis


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Mitosis is cell divisionthat results inthe complete duplication of a

cell

In this example,a cell with fourchromosomes (two pairs)

produces two cells

each with four chromosomes Mitosis takes place

in all cells except sex cells

Mitosis


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Once an egg

has been fertilized,

the developing embryo

grows by mitosis

Mitosis


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During the 1930s and 1940s,paleontologists, population biologists,

geneticists, and others developed ideas that

merged to form a modern synthesisor 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


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They completely rejected Lamarcks idea

of inheritance of acquired characteristics

They reaffirmed the importance of naturalselection

But since then,

some scientists have challenged the emphasis

in modern synthesis

that evolution is gradual

Modern View of Evolution

h i b i i ?


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Evolution by natural selection

works on variation in populationsmost of which is accounted for by the reshuffling

of genes from generation to generation

during sexual reproduction

The potential for variation is enormouswith thousands of genes

each with several alleles,

and with offspring receiving 1/2 of their genesfrom each parent

New variations arise by mutationschange in the chromosomes or genes

What Brings about Variation?


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Mutations result in a changein hereditary information

Mutations that take place in sex cells

are inheritable,whether they are chromosomal mutations

affecting a large segment of a chromosome

orpoint mutations

individual changes in particular genes

Mutations are random with respect to fitness

they may be beneficial, neutral, or harmful

Mutations


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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

Mutations


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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

Neutral Mutations


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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

What Causes Mutations?


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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

Species


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Speciationis the phenomenon of a new species

arising from an ancestral species

It involves change in the genetic makeupof 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

Speciation

All t i S i ti


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A few individuals of a species on the mainland

reach isolated island 1

Speciation follows genetic divergence in a newhabitat.

Allopatric Speciation

All t i S i ti


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Later in time, a few individuals of the new

species colonize island 2In this new habitat, speciation follows genetic

divergence.


All t i S i ti


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Speciation may also follow colonization of

islands 3 and 4

Invasion of island 1 by genetically differentdescendants of the ancestral species!


H S i ti


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More than 20 species of Hawaiian

honeycreepers have evolvedfrom a common ancestor as they adapted to

diverse food sources on the islands

Honeycreeper Speciation

R t f S i ti


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Although widespread agreement exists

on allopatric speciationscientists disagree on how rapidly

a new species might evolve

Phyletic gradualism

Rate of Speciation

the gradualaccumulation of minorchanges

This view was held byDarwin and reaffirmed

by modern synthesis

eventually brings about

the origin of newspecies

R t f S i ti


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Punctuated equilibrium

Rate of Speciation

holds that little orno change

takes place in aspecies

during most of itsexistence

giving rise to a newspecies

in perhaps as little asa few thousand years

then evolutionoccurs rapidly

St l f E l ti


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Divergent evolution occurs

when an ancestral speciesgives rise to diverse descendants

adapted to various aspects of the environment

Divergent evolution leads to descendantsthat differ markedly from their ancestors

Convergent evolutioninvolves the developmentofsimilarcharacteristics

in distantly related organisms Paral lel evolutioninvolves the development

ofsimilarcharacteristics

in closely related organisms

Styles of Evolution


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In both convergent and parallel evolution,

similar characteristics developed independently

in comparable environments

Styles of Evolution

Divergent Evolution


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Divergent evolution of a varietyof placental mammals from a common ancestor

Divergence accounts for descendants

that differ from their ancestors and from one another

Divergent Evolution

Convergent Evolution


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Convergent evolution takes place

when distantly related organisms give rise tospecies

Convergent Evolution

that resembleone another

because theyadapt

in comparable

ways

Parallel Evolution


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Parallel evolution

involves the independentorigin

of similar features in relatedorganisms

Parallel Evolution

Microevolution and Macroevolution


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Microevolution is any change in the

the genetic make-up of a species, and

involves changes within a species

Macroevolution involves changes

such as the origin of a new species

or changes at even higher levels

For example, the origin of birds from reptiles

The cumulative effects of microevolution

are responsible for macroevolution

Microevolution and Macroevolution

Cladistics and Cladograms


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Traditionally, scientists have

depicted evolutionary relationshipswith 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

Cladistics and Cladograms

Phylogenetic Tree


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A phylogenetic tree

showing therelationships

among variousvertebrate animals

Phylogenetic Tree

Cladogram


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A cladogram showing inferred relationships

Some of the characteristics used

to construct this cladogram are indicated

Cladogram


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All land-dwelling vertebrate animals

possess bone and paired limbs

so these characteristics are primitive

and of little use in establishing relationships

among land vertebrates

However, hair and three middle ear bonesare derived characteristics

because only one subclade, the mammals, has them

Evolutionary Novelties


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If considering only mammals,

hair and middle ear bones

are primitive characteristics,

but live birth is a derived characteristic

that serves to distinguish most mammals

from the egg-laying mammals

Evolutionary Novelties

Cladograms


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Three different

interpretationsof the relationships among

bats, dogs and birds

Cladograms

Cladograms


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Bats and birds fly,

which might suggest

a closer relationship

than to dogs

Cladograms

Dogs and birdsdo not appear closely related

Hair and giving birth to live

youngindicate that bats and dogs

are more closely related


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Nevertheless, cladistics is a powerful tool

that has more clearly elucidatedthe relationships among many fossil lineages,

and is now used extensively by paleontologists

Cladistics for Fossils

Evolutionary Trends


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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

Evolutionary Trends


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Phylogenyis 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

Phylogeny

Evolutionary Trends


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Abundant fossils show the evolutionary trends of

the Eocene mammals, Titanotheres

Evolutionary Trends

These extinct relative ofhorses and rhinoceroses

evolved from small ancestors

to giants standing 2.4 m atthe shoulder

developed large horns

and the shape of their skullchanged

Only 4 of the 16 knowngenera are show

Evolutionary Trends


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Size increase is

one of the most common evolutionary trends However, trends are complex

they might reversemore 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 skulllengthening legsreduction in number of toes

These trends occurred at different rates

Evolutionary Trends

Adaptations


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Evolutionary trends are a series of

adaptationsto changing environment

or in response to exploitation of newhabitats

Some organismsshow little evolutionary change

for long periods

Lingula is a brachiopodwith a shell, at least,

that has not changed

significantly since the Ordovician

Adaptations

Living Fossils


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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

Latrimaria (fish)

Gingko trees

Some of these are generalized and can live

under a wide variety of enviroinments

Living Fossils

A Living Fossil


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Latimeriabelongs 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 Living Fossil

A Second Living Fossil


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A Second Living Fossil

Ginkgos

have changed verylittle

for millions ofyears


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But isnt evolution by natural selectiona random process?

If so, how is it possible

for a trend to continue long enoughto account just by chance

for such complex structures as

eyes, wings, and hands?

Randomness in Natural Selection?


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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

Two Steps in Natural Selection

Extinctions


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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 perfectionor greater complexity

Vertebrates are more complexbut not necessarily superiorIn some survival sense, bacteriahave persisted for at least 3.5 billion years!

Natural selection yields organisms adaptedto a specific set of circumstancesat a particular time

Extinctions

Background and Mass Extinction


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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 occurrencebut 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

Background and Mass Extinction


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The mass extinction of dinosaurs

and other animals at the end of Mesozoic Erais well known,

but the greatest mass extinction

occurred at the end of the Paleozoic Erawhen more than 90% of all species died out

Mass Extinction

Evidence in Support of Evolution


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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




69/100

Since Darwins time, studies from additional

fieldsin 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


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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

Is the Theory of Evolution

Scientific?

Theories Must Be Predictive


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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 millions of years from now

Nevertheless, we can make a number ofpredictions

about the present-day natural worldand about the fossil record

that should be consistent with evolutionary theory

if it is correct

eo es us e ed c ve


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If evolution has taken place,

closely related species such as wolves and coyotes

should be similar in anatomy and biochemistry,

genetics, and embryonic development

The oldest fossil-bearing rocks should havevery different fossils than organisms of today

Some Predictions from Evolution

Testable


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Suppose that contrary to evolutionary prediction

wolves and coyotes were not similar

in terms of their biochemistry, genetics

and embryonic development, then

our prediction would fail

and we would at least have to modify the theory

If other predictions also failed,

for example, if mammals appeared in the fossil record beforefishes

then we would have to abandon the theory

and find a better explanation for our observations

Since the theory of evolution can be falsified,

it is truly scientific

Classification


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Classification uses a nested pattern ofsimilarities

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 Canislatrans

Linnaeuss classification is an ordered listof categories that becomes more inclusive

as one proceeds up the hierarchy

Linnaean Classification


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Kingdom

Phylum

Subphylum

Class Order

the coyote, Canislatrans

Animalia

Chordata

Vertebrata

Mammalia Carnivora

Canidae

Canis

latrans

Family

Genus

Species

Most inclusive

Least inclusive

Classificationshared Characteristics


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Subphylum

vertebrata includingfishes,amphibians,reptiles, birdsand mammals,

have asegmentedvertebralcolumn

Only warm-

bloodedanimals withhair/fur andmammaryglands are

mammals

Coyote, Canislatrans


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18 orders of

mammals existincluding orderCarnivora

The FamilyCanidae are

doglikecarnivores

and the genusCanis includesonly closely

related species

Coyote, Canislatrans, standsalone as a

species

y ,

Coyote and Wolf


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Coyote (Canis latrans) and wolf (Canis lupus)

share numerous characteristicsas 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 ordersof the class Mammalia

Shared characteristics

are evidence for evolutionary relationships

y

Biological Evidence


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If all existing organisms descended withmodification

from ancestors that lived during the past,

all life forms should have fundamentalsimilarities:

all living things consist mainly of carbon, nitrogenhydrogen and oxygen

their chromosomes consist of DNA

all cells synthesize proteins

in essentially the same way

gSupporting Evolution

Evolutionary Relationships


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Biochemistry provides evidence

for evolutionary relationships

Blood proteins are 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 ideathat birds descended from reptiles

a conclusion supported by evidence in the fossil record

y p

Structures with Similarities


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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


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Forelimbs of humans, whales, dogs, and birds

are superficially dissimilar,yet all are made up of the same bones,

g

have similar

arrangementof muscles,

nerves and

blood

vessels,

are similarly

arranged with respect to other structures,

have similar pattern of embryonic development

Analogous Structures


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Wings of insects, birds and batsserve the same function but differ considerably

in structure and embryological development

Are any of these wings

both analogous and homologous?

g

Yes, bird and

bat wings

Vestigial Structures


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Vestigial structures are nonfunctional remnantsof structures in organisms that were functional

in their ancestors Why do dogs have tiny,

functionless toes on theirfeet (dewclaws)?

Ancestral dogs had fivetoes 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 Rear Limbs in Whales


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The Eocene-aged whale,

Basilosaurus,had tiny vestigial back

limbs

but it did not use limbs tosupport its body weight.

Evolution in Living Organisms


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Small-scale evolution can be observed today.

For exampleadaptations of some plants to contaminated soils

insects and rodents developing resistance to new

insecticides and pesticidesdevelopment of antibiotic-resistant strains of

bacteria

Variations in these populations

allowed some variant types

to live and reproduce,

bringing about a genetic change

What do We Learn from Fossils?


87/100

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


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Timeswhenmajorgroups ofvertebratesappearedin thefossilrecord

Thicknessof spindlesshowsrelativeabundance

Fossils Are Common


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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 diversificationof horses, rhinoceroses, and tapirs

from a common ancestor are known

as are ones showing the originof birds from reptiles

and the evolution

of whales from a land-dwelling ancestor

Horses and Their Relatives


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This cladogram shows the relationship among

tapirs, rhinoceroses, and horses

Horses and Their Relatives


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These might seem an odd assortment of animals

but fossils and studies of living animalsindicate that they shared a common ancestor

As we trace these animals backin the fossil record,

differentiating one from the otherbecomes increasingly difficult

The earliest members of each group

are remarkably similar,differing mostly in size and details of their teeth

As their diversification proceededthe differences became more apparent

Never Enough


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Of course, we will never have enough fossils

to document the evolutionary historyof all living creatures simply because fossilization

is an incomplete process

The remains of some organisms

are more likely to be preserved than those of othersand accumulation of sediments

varies in both space and time

But several other kinds of evidencesupport the concept of evolution

including molecular biology and paleontology

Summary


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The central claim of evolution is that all organisms

have descended with modification

from ancestors that lived during the past.

Jean Baptiste de Lamarck proposed

the first formal theory of evolution with the mechanism of

Inheritance of Acquired Characteristics

Darwins observation of variation in populations

and artificial selection

and his reading of Malthus essay on population

helped him formulate his idea of natural selection

Summary


94/100

In 1859 Charles Robert Darwin

and Alfred Russel Wallace

published their ideas of natural selection

which hold that in populations of organisms,

wome have favorable traits that make it

more likely that they will survive and reproduce

natural selection

Summary


95/100

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 units

in all organisms

This genetic information is carriedin the chromosomes of cells.

Only the genes in sex cells are inheritable

S


96/100

Summary

Sexual reproduction and mutationsaccount for most variation in populations

Evolution by natural selection has 2-steps

First, variation must exist or arise

and be maintained in interbreeding populations,

and second, favorable variants

must be selected for survival

Summary


97/100

An important way by which new species

evolve is allopatric speciationWhen 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


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Summary


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Background extinctions take place

continually,

but mass extinctions result in marked

decreases

in Earths biologic diversity

The theory of evolution is truly scientific

because we can make observations

that would falsify it

That is, prove it wrong

Summary


100/100

Much of the evidence supporting

the theory of evolution comes from

classification, comparative anatomy,

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

charales darvin

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