EVOLUTION

EVOLUTIONA HISTORY AND A PROCESS

DARWIN DEVELOPED A THEORY OF EVOLUTION• Ideas From Darwin’s Time

– Evolution is the changes that have altered life over a very long time.

– Before Darwin’s hypotheses, there were two predominant hypotheses.• One was species were fixed in time, or did

not change.• The other was that Earth was less than

10,000 years old and was unchanging

DARWIN DEVELOPED A THEORY OF EVOLUTION

– Georges Buffon, a French naturalist in the mid-1700s, suggested that Earth might be older than a few thousand years by looking at fossils.

– His observations concluded that the fossils and some living animals were similar but not exactly alike.

– In the early 1800s, Jean Baptiste Lamarck suggested that life evolves.


– He explained that species are not permanent and that evolution was a process of adaptation.

– Biologists today look upon adaptation as an inherited characteristic that improves the organism’s chances of survival and reproduction.

– The kangaroo’s hind legs and tail are examples of adaptation.

ADAPTATION


– Lamarck also hypothesized an explanation for adaptation that when organisms use or not use certain body parts, certain characteristics develop, and these characteristics would be passed on to the offspring.• This idea was called inheritance of acquired

characteristics.• For example, ancient kangaroos developed

the powerful legs jumping and passed them on to their offspring.


• This characteristic would have to modify the DNA of specific genes in order to be inherited, which has yet to be proven.

– Look at the bonsai tree as an example.• The Voyage of the Beagle

– This was the royal navy ship that Darwin began his five year adventure in 1831, upon graduating from university.

TRAINING, NOT GENETICS


– He wanted to study geology, plants and animals that were encountered while charting the coast of South America.

• Darwin’s Observations– He observed and collected thousands of

specimens of South American plants, animals, and fossils from many diverse ecosystems.

DARWINS TRIP ON THE BEAGLE


– Before his voyage, Darwin held to the belief that the concepts of fixed, or unchanged species described nature; but during the voyage his concepts changed.

– Upon his return to England, he believed that species change as they adapt to their changing environment.

– Throughout South America, Darwin noticed


the plants and animals had a South American character.

– They were distinct from what he had seen in Europe.

– The fossils he collected supported the hypothesis that the current species were descended from ancestral species.

– The Galapagos was his nirvana.


– The Galapagos are volcanic islands about 900 km west of Ecuador.

– He noted that there were many diverse and unique organisms.

– They were similar, but different, to those he found on the mainland of South America.

– He also noted difference among the organisms of each island.

GALAPOGOS ISLANDS


– The inference was that the organisms adapted from the mainland to the islands where they were currently found.

• Ideas From Geology• Charles Lyell, a geologist, influenced

Darwin.• Lyell projected that gradual geologic


changes could explain the physical features of today’s Earth.

– Examples could include erosion of riverbeds over, maybe, millions of years that could result in canyons.

– Earthquakes could cause mountain ranges to push up slowly over millions of years.

HORSESHOE BEND, AN EXAMPLE OF EROSION BY THE COLORADO RIVER


– This would have to mean that the Earth was much older than previously thought.

– Darwin personally experienced an earthquake while in Chile.

– He collected ocean fossils high in the Andes, and thought that earthquakes lifted the sea floor to the mountains, and brought with it the marine fossils.


– Two conclusions related to geology were drawn.• First, mountain building and erosion indicted

Earth being very old.• Second, the slow and gradual processes

occurring over long periods of time could cause vast changes on Earth.

– This gradual change in geology led to Darwin’s evolution hypothesis.

DARWIN AND HIS PUBLIC IMAGE

DARWIN DEVELOPED A THEORY OF EVOLUTION• Darwin Publishes His Theory

– Upon return to England, Darwin became convinced that earth was very old and species can change through time or adapt.

– He read Thomas Malthus’ theories about human suffering due to disease, famine, and homelessness or populations grow too fast (reach their carrying capacity) and outgrow their resources.


– Darwin applied this to all species.– In 1844, Darwin wrote his thesis

outlining his ideas but held on to it in order to accumulate more evidence, consult with his peers, and receive favorable public press.

– Then, in 1858, another British naturalist, came to the same conclusion independently working in Malaysia, causing Darwin to publish his book The Origin of the Species a year later.

DARWIN DEVELOPED A THEORY OF EVOLUTION• Darwin’s Two Main Points

– First, species on Earth originated from ancestral species.• Descendants or earliest organisms spread

into different habitats over millions of years and, there, accumulated different modifications (adaptations) to the diverse ways of life.

• This he called this decent with modification.

DESCENT WITH MODIFICATION

DESCENT WITH MODIFICATION

DESCENT WITH MODIFICATION: HARE vs. JACKRABBITLarge ears of jackrabbit are adaptation to hot environment that allow it to cool off, while the white fur of the snowshoe hare camouflages the animal.


– Second, he argued that natural selection was the mechanism for evolution.• This also is known as survival of the fittest.

– This is the process by which individuals well suited to their environment reproduce more than those that are not.

– Therefore, “Darwin’s theory of evolution” is really natural selection.

INHERITED VARIATION MAKES SNAILS LESS LIKELY TO BE PREY


– The result of natural selection is adaptation and is another way of defining evolution.

– Evolution can also mean the history of life on Earth, from the earliest microbes to the complexity of organisms found today.

REVIEW: CONCEPT CHECK 14.1, page 2981. How did the work of Lyell and Malthus

influence Darwin as he developed his theory of evolution?

2. What characteristics of the Galapagos Islands were particularly important for Darwin?

3. What is natural selection?4. Which of the following is an adaptation: the

sharp teeth of a house cat, or a scar on the cat’s ear? Explain.

EVOLUTION HAS LEFT MUCH EVIDENCE• The Fossil Record• Fossils, as you know, are preserved

remains of organisms that lived in the past.

• Most are found in sedimentary rocks.– These are formed from sand and silt that

has eroded from the land and deposited and

EVOLUTION HAS LEFT MUCH EVIDENCE

carried by waterways to the seas and swamps, where they settle to the bottom.• Over a long period of time, there comes to be

lots of this material piling up on top of one another, compressing the older sediments on the bottom into rock.

• Layers, or rock strata, form when the rates of sedimentation or types of particles forming the sediments vary over time.

SEDIMENTARY ROCK

SEDIMENTARY ROCK

FOSSILS AND SEDIMENTARY ROCK


– Fossils form if they are caught in the sediment after they die and are preserved.

– The oldest layer are at the bottom and youngest at the top.

– The fossil record is the chronologic collection of the remains within each layer, and provides historical evidence of Earth’s changing life.


– The oldest fossil (chemical traces) was found in Greenland and dates to 3.8 billion years ago.

– The first life on Earth was prokaryotes (bacteria and archaea) found in rocks about 3.5 billion years old.

– The younger layers of rock give the evolution of the various eukaryotic organisms.


– The first nuclear cell, a single cell, was found to be 1.5 billion years old.

– Extinct species’ fossils aid in reconstructing the earliest days on Earth.

– Paleontologists, who study ancient life, have found that whales evolved from land animals that had four limbs, but lost the hind limbs eventually.

EVOLUTION OF WHALES

EVOLUTION OF WHALES

EVOLUTION HAS LEFT MUCH EVIDENCE• Geographic Distribution

– Darwin noticed the differences and similarities of organisms on the different continents he visited.

– From these observations, he thought that the modern organisms evolved from those in the past.

– He questioned the similarity between animals


of the South American tropics and the animals of the South American desert; and their non-similarity to animals in the African tropics.

– Why do most of the marsupials (pouched mammals) live in Australia and few placental animals (complete their embryonic development before birth), deer and squirrels, live there.

GEOGRAPHIC DISTRIBUTION


– Placental mammals can thrive in Australia.

– The belief is that the diverse marsupial species evolved from marsupial ancestors on an island continent where no placental animals were found.

– Geography , according to Darwin, played a strong part in what organisms were found where.


– Islands with similar climates in different parts of the world contained in the past and present organisms that identify with the closest large land masses.

• Similarities in Structure– There are similarities among structures

of different species that provides evidence of evolutionary history.


– All mammals have the same skeletal parts in their forelimbs, but the functions might be different.• For example, there are similarities in

structure between the bat’s wing and the whale’s flipper, but the function couldn’t be more different.

– Similar structures in species that share a common ancestor are homologous structures.

HOMOLOGOUS STRUCTURES

HOMOLOGOUS STRUCTURES


– Looking at homologous structures supports the evidence that adaptation takes place from the ancient species to the more modern species.

– Similar structures take on new functions with adaptation which supports the descent with modification theory.

– Another interesting fact is vestigial structures,


which are remnants of structures that at one time had important functions , but in the more modern species, have no or little function.

– This can be seen, also, as similar structures having importance in one species of mammals but not in others.

– Often the vestigial organs are reduced in size, such as the hind limbs of mammals with four


limbs but small vestigial hipbones in whales.

– The natural selection theory supports the explanation for vestigial structures and the known process of inheritance, which is the survival and reproduction of individuals with genes for reduced versions of the structures.

– The presence of these structures gives truth to the theory that certain species descended from a common ancestor.

VESTIGIAL STRUCTURES

EVOLUTION HAS LEFT MUCH EVIDENCE• Similarities in Development

– Darwin also used comparison of different organisms to prepare his hypothesis.

– He noted that embryos of closely related organisms have similar stages of development.• Vertebrates have pouches on the sides of

their throats in one of their embryonic stages.• Fish, frogs, snakes, birds, and primates look

alike in this stage.

SIMILARITIES IN DEVELOPMENT

SIMILARITIES IN DEVELOPMENT


– As these different vertebrates develop, they assume their own distinctive features.• For example, there is a common pattern in

the development of forelimbs in different mammals.

• Molecular Biology– Recently, there is clear evidence in

evolution from the molecular history of organisms.


– While there are similarities in sequencing, it is less so in unrelated individuals than in related individuals.

– Biologists are looking at the sequencing of different species as to the genes and proteins produced.

– If they match closely, then their sequencing must have been inherited from a recent common ancestor.


– The opposite is also true, that the less they resemble each other in DNA and protein sequencing, the less likely they have a common ancestor.

– With DNA and protein analysis, biologists can test these hypotheses.

– Fossils and anatomy relate humans, chimpanzees, and gorillas.


– This hypothesis is testable: if the humans and primates are related, then they would share similar DNA and protein synthesis.• Data from the amino acid sequencing of

hemoglobin support this hypothesis.– There is only 5% difference in the

sequencing between humans and chimpanzees.

AMINO ACID SEQUENCING BETWEEN PRIMATES

AMINO ACID SEQUENCE BETWEEN SPECIES

YOUR COUSIN: A CHIMPANZEE??


– Darwin ‘s hypothesis that all life forms are related has been shown to be true by the common genetic code shared by all species.

REVIEW: CONCEPT CHECK 14.2, page 3041. Why are older fossils generally in

deeper rock layers than younger fossils?

2. How can evolutionary theory explain why Australia is home to relatively few native placental mammals?

3. What are homologous structures?4. What can you infer about species that

differ significantly in their DNA sequences?

DARWIN PROPOSED NATURAL SELECTION AS THE MECHANISM OF EVOLUTION• Darwin’s Theory of Natural Selection

– Populations are groups of individuals living in the same area at the same time.

– A species that came from a mainland, over time, living on an isolated island makes up a separate population that would adapt to the local conditions.

– Eventually, the isolated population would

DARWIN’S FINCHES

DARWIN’S FINCHES

DARWIN PROPOSED NATURAL SELECTION AS THE MECHANISM OF EVOLUTION

become more and more different, with the eventuality that a separate species would evolve.• This is what happened to Darwin’s finches on

the Galapagos.– Observations Lead to a Question

• One finch from South America gave rise to 13 different finches on the Galapagos.


• The explanation that these different finches adapted to their different habitats on the different islands and developed different beaks in response to the food available.

• Darwin would say this happened because of natural selection.

– More Observations Lead to an Idea• Natural selection was based on two sets of

observations.

NATURAL SELECTION


• The first was drawn from Malthus’s ideas about humans and recognized that all species can produce numbers greater than can be supported.

• Remember carrying capacity and competition if too many of a species occupy an habitat.

• Most of the time, only a small amount of offspring will survive.

• The second observation was the variation seen among the individuals of a population.


• Remember that variation is that concept that refers to the differences among members of the same species.

– This variation can be and is inherited.• From these two observation came the theory

of natural selection which tells us that individuals with inherited traits are best suited to their environment and will survive and reproduce than those less fit.

• This is also known as survival of the fittest.

NATURAL SELECTION


• Passing these traits to each of the next generation produces only advantageous traits in the new offspring.

• According to Darwin, natural selection could cause two isolated populations of the same species to become separate species by adapting to the different environments, such as the finches did.

• Artificial Selection– Artificial selection is selective

breeding of


plants and animals to produce offspring with selected traits that are valued.

– Darwin noted that breeders allowed only those plants and animals with the desired traits to reproduce, and that over s relatively short period of time a great deal of changes could be produced.

– Naturally, his conclusion was that over

ARTIFICIAL SELECTION


thousands of generations, natural selection could cause major changes.

– The major difference between the two is that in one humans select the trait desired in the offspring while in the other nature selects what is important to survive in that particular environment.

– Evolutionary adaptation is the result.

DARWIN PROPOSED NATURAL SELECTION AS THE MECHANISM OF EVOLUTION• Pesticides-Natural Selection in Action

– Insects have the uncanny ability to adapt very well, especially to the various pesticides utilized.

– Early applications to rid fields of pests works great but then adaptation occurs and less and less insects are eliminated.

– An example is the flour beetle (Tribolium

PESTICIDE RESISTANCE

PESTICIDE RESISTANCE


castaneum, for which malathion worked well but now, even in high doses, has no effect.

– Genetically, each generation beetle passed on to the next generation an even greater resistance to the pesticide, and with evolutionary changes the pesticide was no longer efficacious.

– Therefore, natural selection offers two key points.


– Natural selection is a process of screening traits that are available.• The pesticide did not create the resistance

but selected those that developed it and survived

– Natural selection likes those characteristics in varying populations that fit the specific environment.• There was no advantage to pesticide

resistance until the pesticide application changed the environment.

REVIEW: CONCEPT CHECK 14.3, page 3081. In Darwin’s view, what conditions

lead to a struggle for existence among individuals in a population?

2. What is the goal of artificial selection?

3. Why does a specific pesticide become less effective over time?

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL• Populations and Their Gene Pools

– Populations are groups of individuals belonging to the same species and is the smallest level in which evolution can take place.

– It is a mistaken belief that individuals evolve and not populations.

– Natural selection affects individuals but it is

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL the entire populations that adapts over

time.– Gene pools are composed of all the

alleles in all individuals that make up a population.

– This is where the next generation “draws’ its genes from and where genetic variation is born and stored.

– Certain animals, such as horses, have different coloration due to each horse’s own

GENE POOLS

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL combination of genes.

– This is the result of genetic recombination, seen more frequently in which reproduction is sexual.• Meiosis and gene shuffling produces the

different combinations.• Changes in Gene Pools

– Genetic variation, caused by mutations and recombination, are random.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– Outcomes of these gene recombinations

can’t be predicted but natural selection is not random.

– Environment dictates survival and reproductive success so those alleles that lead to this are more common.

– Frequency of alleles, or how often certain alleles appear in a gene pool, can change.

GENE POOLS AND FRQUENCY

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– One can merge Mendel’s and Darwin’s

theories to come up with evolution based on genetic changes.

– Microevolution is the changes in the frequencies of alleles from generation to generation.

– Some populations do not change or undergo evolution.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– This is known as the Hardy-Weinberg

equilibrium, and means that the frequency of alleles in a gene pool remains constant over time.

– While it is rarely seen for long in nature, the concept allows for a baseline to recognize when that gene pool is changing.

– Genetic drift and natural selection account for changes in a gene pool.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL• Genetic Drift

– Changes in gene pools of populations, due to chance, is known as genetic drift.

– In the slide that follows, one can see two phenotypes due to three different genotypes.

– Chance dictates which plants reproduce, so that by the third generation, there could be no recessive plants.

GENETIC DRIFT

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– While genetic drift can affect all

populations, it is most felt in smaller populations, because probabilities have less of a chance to be correct.

– The Bottleneck Effect• Major disasters have profound effects on

sizes of population, e.g. the recent earthquake in Haiti.

• Reduction in population results in reduction of the gene pool.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL• Chance will allow some alleles to be more

frequent in the survivors, others to be eliminated altogether.

• This genetic drift is known as the bottleneck effect, and decreases genetic variation in populations.

• This could result in loss of adaptation to environments.

– Cheetahs were affected by the last ice age and recently hunted almost to extinction.

– Their pool have decreased as a result and they may not be able to adapt to disease or other challenges.

BOTTLENECK EFFECT

BOTTLENECK EFFECT

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– Founder Effect

• When isolated islands are inhabited, they are done so by only small colonies with a smaller genetic make-up which represents the gene pool of the larger population from whence the colonies came.

• Chance will reduce this variation.• This is known as the founder effect because

the change relates to the genetic make-up of the founders of the colony.

– A prime example is Darwin’s finches.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL• Gene Flow and Mutation

– Gene Flow• Exchanges of genes with other populations is

gene flow, and occurs when animals in heat exchange gametes between populations.

• This is seen often in flowers when pollen can be exchanged between different populations .

• This results in the reduction of genetic differences between populations.

GENE FLOW

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL• Mutation

– Remember, mutation is any change in the organism’s DNA.

– Natural selection or genetic drift (or both) can influence whether the frequency of a new mutation increases in a population.• The albino deer has the advantage in the

winter but lacks it the other three seasons.• This can and does present a dilemma that

would

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL hinder the frequency of this allele.

– Over a long period of time, mutations play key roles as the original sources of genetic variation in natural selection.

– These become most important in asexual reproduction where cloning occurs.• Bacteria can produce favorable mutation

rapidly while in sexual reproduction variation occurs

MUTATIONS AND ALBINO DEER

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL because of scrambling of existing alleles,

including those that occurred as a result of mutations in earlier generations.

• Natural Selection and Fitness– Microevolution occurs with genetic drift,

gene flow, and mutation but not necessarily adaptation as these can be due to chance.

– Only natural selection leads to adaptation.

“STRUGGLE” & “FITTEST”

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– With natural selection, one gets chance

and sorting.• Chance from mutations and genetic

recombination– Sorting, which is not random, comes

from differences in reproductive success among the members of the varying population.

– Struggle for existence or survival of the fittest are used to describe natural selection.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– Struggle or fittest involves biological

definitions, not competitions.– Fitness is the contribution that

individuals make to the gene pool of future generations compared to the contributions of other individuals.

– All that really counts in fitness is reproductive ability.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL• A Return to the Galapagos

– “Darwin’s finches” are one of the best living laboratory specimens of natural selection.

– Rosemary and Peter Grant and their students have studied these finches each year on Daphne Major, an island in the Galapagos no bigger than a football field.

ROSEMARY AND PETER GRANT

DAPHNE MAJOR

FINCHES OF DAPHNE MAJOR

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– Using the data collected from their

studies, they have been better able to explain natural selection.

– The medium ground finches use their beaks to crush seeds, not large ones but mostly small ones because they are easier to crush.

– There are dry and wet seasons with more or less small seeds, so to survive the birds must eat the large seeds as well.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– Some birds have larger beaks that allow

them to more easily crush the larger seeds, and therefore, increase their survivability.

– These larger beaks are then passed on to future generations, and reproduction is increased in this population while smaller beak birds do not reproduce.

MICROEVOLUTION IS A CHANGE IN A POPULATION’S GENE POOL– When wet seasons return, the smaller

beaked birds then flourish and reproduce in greater numbers.

THE GRANTS’ RESULTS

REVIEW: CONCEPT CHECK 14.4, page 3161. What is a gene pool?2. How has genetic drift affected the world’s populations

of cheetahs?3. Describe what is meant by a “biologically fit”

organism.4. Describe the Grant’s hypothesis about how

environmental conditions led to microevolution among the finches of Daphne Major.

5. What are two main forces of evolutionary change in gene pools?

EVOLUTIONARY BIOLOGY IS IMPORTANT IN HEALTH SCIENCE• Natural Selection and Sickle Cell

Disease– Sickle cell disease creates an abnormal

shape to the red blood cell resulting in decreased hemoglobin capacity and clumping of the cells.

– In some African communities, its incidence is 1:25.

– It is caused by a recessive allele and you must be homozygous.

EVOLUTIONARY BIOLOGY IS IMPORTANT IN HEALTH SCIENCE– Heterozygous individuals are carriers

and also possess resistance to malaria.– The heterozygous individual is found in

greater proportions in those areas of Africa where malaria is indigenous

– While only 4% are homozygous, 32% are heterozygous and thus protected from malaria.

SICKLE CELL DISEASE AND ALLELE

EVOLUTIONARY BIOLOGY IS IMPORTANT IN HEALTH SCIENCE• Evolution of Antibiotic Resistance in

Bacteria– Antibiotics are used to kill or slow the

growth of bacteria.– Too much usage, however, can lead to

antibiotic-resistant populations caused by natural selection, just as in pesticide resistance in insects.

REVIEW: CONCEPT CHECK 14.5, page 3191. Under what conditions is the sickle

cell allele beneficial to a heterozygous individual?

2. Identify a possible risk of overuse of antibiotics.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES• What is a Species?

– The biological species concept defines a species as a population or group of populations where the members have the ability to breed with one another in nature and produce fertile offspring.

– Members of one species, however, cannot successfully interbreed with members of other species.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES• From Microevolution to

Macroevolution– Evolution can be explained by

microevolution and adaptation, but if that were all that happened, then Earth’s inhabitants would only be a highly adapted version of the first form of life.

– If microevolution refers to the change in the allele frequencies within a population, then macroevolution refers to more dramatic biological changes, many found in fossil records.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– Macroevolution refers to more

dramatic biological changes, many found in fossil records.• These include the origin of different species• The extinction of species• The evolution of major new features, such as

wings or flowers– Speciation is the origin of new species

which is the main focus of macroevolution.

SPECIATIONWith speciation comes biological diversity.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES• Reproductive Barriers Between

Species– Frogs don’t mate with flies or ferns.– Do species that are not so different

mate?– Remember, a species is a group of

organisms that can reproduce.– Can species that are similar and closely

related interbreed?

EASTERN AND WESTERN SPOTTED SKUNKS: REPRODUCTIVE ISOLATION

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– The example in the textbook is the

western and eastern spotted skunks, which don’t interbreed even when their habitats overlap.

– They don’t because of reproductive isolation and include some of the following ideas.

– Timing• They have different breeding seasons, as

these skunks do (western in fall, eastern in late winter).

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– Behavior

• The two similar species may have different courtship or mating behaviors.

• The example here is the eastern and western meadowlark, which have different songs, even though their ranges overlap.

– Habitat• They are adapted to different habitats, even

though they are in the same general location, such as the

EASTERN AND WESTERN MEADOWLARK: BEHAVIORAL ISOLATION

THREE-SPINED STICKLEBACK FISH

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES• three-spined sticklefish of British Columbia

which inhabit different parts of the same lake but don’t interbreed.

– Other Reproductive Barriers• Dissimilar reproductive structures• Transfer of pollen by insects to plants of a

single species• Those that present themselves after

fertilization– Hybrid zygotes that fail to develop or are infertile

as adults

HORSE→MULE=DONKEY: REPRODUCTIVE ISOLATION

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– Reproductive isolation results from a

combination of two or more barriers.– These present themselves as an effect of

adaptation.– This could account for the differences

between the eastern and western spotted skunks and presented itself in their ancestors when the two species were isolated in different locations.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– New species arise if reproductive

isolation keeps species separate after the species arise.

• Geographic Isolation and Speciation– Because of the ever changing geography

of Earth, populations of species can be separated.

– Mountain ranges, glaciers, earthquakes, and island colonization can separate populations.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– This is called geographic isolation.

– A prime example is the antelope squirrel where two species became separated by the Grand Canyon.

– Once a small splinter population becomes separated, new species can develop.

– It can follow its own evolutionary course.

ANTELOPE SQUIRRELS: NORTH RIM vs. SOUTH RIM

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– This is where genetic drift comes into

play where changes in allele frequency caused by the genetic drift and natural selection can accumulate in the separate population, causing it to be less and less like the main population.

– Many population fail to survive this isolation.

– Speciation occurs only if one population can

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– no longer breed with the other

population, even if they come back into contact.• In one, the changes do not prevent

interbreeding, and the populations remain one species.

• In the other, evolution has prevented them from interbreeding and two species result.

• Adaptive Radiation– Islands seem to have conditions that

favor speciation.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– Only a few organisms can be the first to

inhabit a new island, and they undergo evolutionary change to survive.

– These “new” organisms can move on to other islands in the group where “new” species also evolve.

– New and varying species may evolve through genetic drift and adaptation to the different habitats.

ADAPTIVE RADIATION

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– This results in adaptive radiation,

which is evolution from common ancestors that result in new and diverse species that have adapted to the new environments.• One of the best examples of adaptive

radiation is the Hawaiian Islands.• The Tempo of Speciation

– Species can evolve gradually or rapidly.

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– This is known as punctuated

equilibrium with species diverging in spurts of rapid change.

– While over a period of a few million years may seem long, over the lifetime of Earth, this is but a short period.

– Fossil records indicate that successful species last about one to five million years.

EVOLUTIONARY TIME

GRADUALISM vs. PUNCTUATED EQUILIBRIUM

THE DIVERSITY OF LIFE IS BASED ON THE ORIGIN OF NEW SPECIES– Most of the species changes occur in the

first 50,000 years which is a very short period of time.

– This theory does not negate the theory of natural selection because adaptation and natural selection occur when a species is young.

REVIEW: CONCEPT CHECK 15.1, page 3301. Why are donkeys and horses considered

different species?2. What is macroevolution?3. Give an example of a reproductive barrier

that may separate two similar species.4. Describe conditions that could make a new

island a likely place fro adaptive radiation.5. How does punctuated equilibrium relate to

Darwin’s theory of natural selection?

EVOLUTION IS USUALLY A REMODELING PROCESS• Refinement of Existing Adaptations

– Adaptations such as fins and flippers for swimming animals, bodies sleek for flying, eyes for sight, or flowers for attraction are forms of natural selection.

– Eyes, for example, can be seen in various stages of development in mollusks such as squids, octopuses, snails, and clams.

DEVELOPMENT OF EYES IN MOLLUSKS

DEVELOPMENT OF EYES IN MOLLUSKS

EVOLUTION IS USUALLY A REMODELING PROCESS• Adaptation of Existing Structures to

New Functions– Over time, certain existing structures in

organisms have evolved from their original function to something different.

– Chitin, the exoskeleton of arthropods (insects, spiders, scorpions, and lobsters) is one example.

EVOLUTION IS USUALLY A REMODELING PROCESS

– Originally in the ocean the chitin protected the animal from predators, while on land it took on an additional function, to protect it against loss of body water by evaporation.

– Penguins’ flippers have evolved from wings for flight to flippers for swimming.

• Evolution and Development– Embryology can answer some of the

questions

ARTHROPODS AND CHITIN

PENGUINS’ FLIPPERS


that arise as to the evolutionary remodeling of body forms.

– Embryology is the study of the development of multicellular organisms from fertilized eggs to formed organisms.

– Embryologists look at the genes that control the development of organisms.

– One study is of homeotic genes that control the placement of body parts.


– Mutations in this area can lead to flies developing legs where antennae should be, or, in most cases, less subtle changes in the developmental process.

– Remodeling can occur over the short term or long term depending on the environment of the organism.

– Development of feet in different salamanders is an example.

EVOLUTION IS USUALLY A REMODELING PROCESS• The tree salamander vs. the ground

or water salamander have different feet depending on the usage.– Shorter toes and more webbing in the

tree salamander occurs because growth of these appendages ends sooner than the rest of the body as it adapts to the tree.

GROUND AND TREE SALAMANDERS

REVIEW: CONCEPT CHECK 15.2, page 3341. How can evolution explain the range of

complexity of eyes in modern organisms?

2. Give an example of evolutionary remodeling of an existing structure to a new function.

3. Identify one possible event during an organism’s embryonic development that can result in a change in body form.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY• How Fossils Form

– We previously learned that fossils form after being covered by layers of sediment.

– The hard parts are preserved while the soft parts decay.

– In some cases, minerals from groundwater will penetrate the tissues and replace the organic material which then becomes petrified.

FOSSIL DEVELOPMENT

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– In rare cases, some of the organic

material still exists and DNA can be analyzed form it.

– Footprints, burrows, waste material from the organisms gives clues as to its ambulation, diet, habitat, and digestive process.

• The Fossil Record and Geologic Time Scale– Fossil records tell us about

macroevolution.

MAMMOUTH REMAINS

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– They tell us the history of Earth.

– The geologic time scale organizes earth’s history into three ages: Paleozoic, Mesozoic, and Cenozoic eras.

– The eras are further divided into shorter time spans called periods.

– Periods can be divided into epochs.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– Time between periods is marked by

major changes in living organisms.– At the beginning of the Paleozoic Era

(Cambrian period), multicellular organisms with hard parts developed.

– Boundaries between eras and periods are also delineated by extinctions.

GEOLOGIC TIME SCALE

GEOLOGIC TIME SCALE

GEOLOGIC TIME SCALE

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY• Dating Fossils

– Relative ages of fossils reflect the order in which groups of species existed compared to each other. • Younger on top and older on bottom.

– Actual ages, or absolute ages, of fossils is made by radiometric dating, which is based on the measurement of certain radioactive isotopes in objects.

RELATIVE DATING

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– Radiometric dating utilizes

measurements of radioactive isotopes in objects.• It is utilized to measure absolute ages of

rocks and fossils.• All radioactive isotopes have a standard rate

of decay.– It’s half-life is that amount of time that

it takes for 50% of the original sample to decay.

RADIOMETRIC DATING

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– Half-lives are not affected by

temperature, pressure, or any other environmental conditions.

– Radioactive isotopes with long half-lives are used to date rocks.• Uranium-238 is used to date rocks from

Precambrian time, since it has a half-life of 4.5 billion years.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY• There is no U²³⁸ in living organisms, but it

occurs in molten lava and volcanic rock.• With the formation of the volcanic rock, no

additional U²³⁸ is incorporated.• The original amount of isotope decays,

eventually forming lead(Pb)-206.• Measuring and comparing U²³⁸ to Pb²⁰⁶, dating

can be made.• Similarly, fossils found in these rocks can be

dated.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– Fossils, themselves, can also be dated

since they contain isotopes of carbon that accumulated when they were alive (C¹² to C¹⁴).• Plants utilize both for photosynthesis and

animals consume plants for food.• After the animal dies, the decay continues,

and the changes in C¹⁴ to C¹² can be measured with calculations used to determine how long the organism has been dead.

RADIOACTIVE DATING

RADIOACTIVE DATING

CARBON DATING

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– This carbon dating is only good for

recent fossils since C¹⁴ has a half life of 5,730 years. If the fossils are older than 50,000 years, longer half-life isotopes (U²³⁸) must be used.

• Continental Drift and Macroevolution– Earth is made up of seven tectonic

plates.– Landmasses and oceans are part of

these plates and change position as a result of movement known as continental drift.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– The plates are known to move at a rate

about 1 to 16 cm per year.• For example, North America and Europe are

drifting apart about 2 cm per year.• Finding similar fossils on different continents

can be attributed to this plate movement.– Similar Mesozoic fossils were found in Brazil and

Africa.– Plants and animals of Australia are drastically

different than the rest of the world because Australia became an isolated landmass and the organisms evolved independent of those on other continents.

PLATE TECTONICS

CONTINENTAL DRIFT

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– About 250 million years ago, at the end

of the Paleozoic Era, a Pangaea was present or one landmass (or supercontinent).

– This resulted in: lower sea levels, draining of shallow coastal seas, destruction of shallow ecosystems, drier and more extreme climate changes inland, competition among species, and ultimately extinction of large amounts of species.

PANGAEA

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– About 180 million years ago, the

Pangaea began to drift apart and each land mass became isolated and created separate evolutionary beginnings.

– Each species on each continent would develop based on their environment and would have diverged in their evolution as they adapted.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY• Mass Extinctions

– Examining fossil records reveals that there have been long periods of stability interrupted by brief episodes of great species loss which are known as mass extinctions.

– At the end of the Cretaceous period, about 65 million years ago, the dinosaurs began to disappear.

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– Before that there were dinosaurs for 150

million years.– In less than 10 million years, they

disappeared altogether.– Scientists have been as a loss for the

reasons for this calamity but look at the receding seas, cooling climate, a meteor striking the Yucatan Peninsula causing pollution and lack of photosynthesis for plant production.

DINOSAUR EXTINCTION

THE FOSSIL RECORD PROVIDES EVIDENCE OF LIFE’S HISTORY– There have been about 5 or 6 mass

extinction recorded in the history of the Earth, over the last 600 million years.• 90% of the marine animals were lost at the

end of the Permian period.– After each of these periods, there has

been adaptive radiation of some of the survivors, for example mammals at the end of the Cretaceous period.

REVIEW: CONCEPT CHECK 15.3, page 3401. Which parts of organisms are most commonly

found as fossils?2. What main characteristics distinguishes the

fossil record of the Paleozoic Era from that of the Precambrian Era?

3. How are the relative ages of fossils in sedimentary rock determined?

4. How does a mass extinction change conditions for species that survive?

EVOLUTION

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