What is evolution?•Evolution is a process that results in heritable changes in a population spread over many generations.

•“Evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next."

How does Evolution Occur?• Jean Baptiste Lamarck 1744-1829 was one

of the first to propose that organisms change through time-

1. The Principle of Use and Disuse– A change in the environment produced

a need to change in the animals– If an animal uses one part of its body

frequently, that part will become stronger

– If they don’t use a part, it will become smaller and disappear.

animation

Lamarck cont’d

2. The Principle of Inheritance of Acquired Traits

He assumed these acquired traits could be passed on to offspring.

Charles Darwin• Influences:

– geologist Charles Lyell• Wrote Principles of Geology; claimed that

geologic forces produced changes on Earth in the past and those same forces will continue to produce changes in the future.

– Economist Thomas Malthus• Wrote in Essay on the Principle of

Population that “population growth would always overpower food supply growth, creating perpetual states of hunger, disease, and struggle”

If evolution was a car, the theory of natural

selection would be the engine • The basic ideas of evolution were discussed

long before there was any scientific research to support them.

• The evolutionary concept was never able to gain any real steam because it lacked a mechanism. – Scientists wanted to believe that species

evolved from one form to another, but had no plausible process to make it happen.

– The theory of natural selection is just that! animation

Darwin’s Theory of Natural Selection

1.  Overpopulation- All species have the potential to

overpopulate the earth, but usually remain stable over time.

2. Variation- Due to variation, different individuals among populations have different traits

3.  Competition- a large # of the population must die at an early age.

Darwin’s Idea Cont. 4.  Survival of the Fittest-

members of a population whose trait makes them better adapted to their environment are more likely to survive to reproductive age and produce more offspring.

5.  Reproduction- members of a population whose trait makes them better adapted are more likely to reproduce.

6.    Speciation- given time, the process of evolution by natural selection can account for the formation of new species and thus for the diversity of life on earth.

So where does all this variation come from?

-August Weismann

Kinds of variation:- environmental versus genetic

Sources of variation:- mutation, genetic recombination

Vocabulary to understand:• Population

– a group of individuals living in the same geographical area and sharing a common gene pool

• Gene Pool – the sum of all genetic information carried by the members of a

population • Mutation

– any heritable change in DNA (gene-level and the chromosome-level)

• Gene Flow– The transfer of alleles between populations through

interbreeding• Natural Selection

– Differential survival and reproduction of organisms with a result of increase in frequency of best adapted traits.

• Nonrandom Mating– artificial selection

This stud bull is the product of generations of selective breeding that has resulted in a double muscled freak that can hardly walk

Populations and Gene Pools

What’s the difference between microevolution and macroevolution?

• Microevolution is change within species which can occur over dozens or hundreds of generations.

• Macroevolution usually involves much longer periods of time and includes the origin of new species.

What is a gene pool?

The collection of alleles available among reproductive members of a population

Evolution occurs on the population level

• A population is a group of individuals of the same species in a given area whose members can interbreed.

• Because the individuals of a population can interbreed, they share a common group of genes known as the gene pool.

• Each gene pool contains all the alleles for all the traits of all the population.

• For evolution to occur in real populations, some of the gene frequencies must change with time.

Gene Frequencies and H-W

• The gene frequency of an allele is the number of times an allele for a particular trait occurs compared to the total number of alleles for that trait.

Gene frequency = the number of a specific type of allele / the total number of alleles in the gene pool

• An important way of discovering why real populations change with time is to construct a model of a population that does not change. – This is just what Hardy and Weinberg did. – Their principle describes a hypothetical

situation in which there is no change in the gene pool (frequencies of alleles), hence no evolution.

The Hardy-Weinberg Theory

This law states an equilibrium of allele frequencies in a gene pool (using a formula p2 + 2pq + q2) remains in effect in each succeeding generation of a sexually reproducing population if five conditions are met: 1. Large population-

The population must be large to minimize random sampling errors.

2. Random mating-There is no mating preference. For example an AA male does not prefer an aa female.

3. No mutationThe alleles must not change.

4. No migration –Exchange of genes between the population and another population must not occur.

5. No natural selection- Natural selection must not favor any particular individual.

• These conditions of the Hardy-Weinberg law are rarely met

• Allele frequencies in the gene pool of a population do change from one generation to the next– thus resulting in evolution.

• The H-W equation provides a baseline by which to judge whether evolution has occurred.

The effect of natural selection on gene frequencies can be quantified.

If a change in allele frequencies occurs over time, you can assume evolution is happening.

A hypothetical “gene pool”

• Find the Frequencies of A and a and the genotypic frequencies of AA, Aa and aa.

Solution: f(A) = 12/30 = 0.4 = 40% f(a) = 18/30 = 0.6 = 60%

Then, p + q = 0.4 + 0.6 = 1 and p2 + 2pq + q2 = AA + Aa + aa

= .16 + .48 + .36 = 1

As long as the conditions of Hardy-Weinberg are met, the population can increase in size and the gene

frequencies of A and a will remain the same.

Thus, the gene pool does not change.

• Now, suppose more 'swimmers' dive in as shown in What will the gene and genotypic frequencies be?

Solution: f(A) = 12/34 = .35 = 35 % f(a) = 22/34 = .65 = 65%

f(AA) = .12, f(Aa) = .23 and f (aa) = .42

• The results show that H-W Equilibrium was not maintained. – The migration of swimmers (genes) into the pool (population)

resulted in a change in the population's gene frequencies. – If the migration were to stop and the other agents of

evolution (i.e., mutation, natural selection and non-random mating) did not occur, then the population would maintain the new gene frequencies generation after generation.

– It is important to note that a fifth factor affecting gene frequencies is population size.

• The larger a population is, the number of changes that occur by chance alone becomes insignificant.

• In the previous analogy, a small population was used to simplify the explanation.

How much variation does a large population of sexually reproducing

organisms have in their gene pool?

•Typically about 0.5% of the DNA bases are variable

• In fruit flies there are 165 million base pairs so ~1 million nucleotides sites differ.

•In humans with 3 billion base pairs there are about 15 million different/variable nucleotides).

Mutation Rate

• Gene mutations result in new alleles, and are the source of variation within populations.

• Due to DNA replication and DNA repair

mechanisms, mutation rates of individual genes are low, but many genes + many individuals= new mutations all the time.

                                                       

Mutations and Peppered MothsIn 1850, f(L)= .95 and f(l) = .05 (light colored moths on light colored trunks were camouflaged)

In 1900, f(L) = .05 and f(l) = .95

50 generations later (light lichen was killed by pollution, now the dark tree trunk was exposed so light colored moths became easy prey for birds).

Positive, Negative, or Neutral: Impacts of mutations

• Mutations are random and unpredictable• Some are lethal and kill individuals

before they are born• Some are harmful but masked by a

dominant allele (each of us carry 7-8 lethal recessive genes)

• Some are neutral and have little to no affect on an organisms long term survival.

• Some are beneficial and help the organism survive to reproductive age and reproduce

Gene Flow

• the exchange of alleles– Alleles move through populations by

interbreeding, as well as by migration of breeding individuals.

– Gene flow can increase variation within a population by introducing new alleles produced in another population

Genetic Drift

• random changes in the gene pool– Genetic drift causes gene pools of two isolated

populations to become dissimilar as some alleles are lost and other are fixed  

– This causes a reduction in the frequency of the heterozygotes over time.

– The smaller the population size the faster the effect is seen

Why does it affect small populations more?

• In a small population, allele frequencies are likely to be atypical just by chance.

• If you were to toss a coin 1000 times and get heads 750 times you would be very surprised.

• If you tossed a coin 4 times and got 3 heads, you would not be so surprised!

• Chance has a greater influence upon gene frequencies in a small population

When is genetic drift likely to occur in nature?

• Most populations are large enough that genetic drift does not occur

• Some populations crash in numbers due to natural disasters or over-harvesting by humans(“bottleneck effect”- examples will be provided later)

• Another example is when a new habitat (e.g. an island) is colonized by just a few dispersing individuals (“founder effect”)

• The suddenly small population may, purely by chance, contain a different frequency of different genotypes that the original large population.

More on the Founder Effect

• Genetic drift can occur when a small number of individuals from a large population emigrate to a new area.

•The small number of emigrants are likely to have an genetic structure that differs, purely by chance, from the main population

•In the 1700’s 200 German Amish immigrated to Pennsylvania to start a community. •These people carried a high concentration of a mutation which causes a form of polydactylism.

•Individuals in this group tended to marry within so there's a greater likelihood that the recessive genes of the founders will come together in the cells that produce offspring.

An Example of Founder’s Effect:

InbreedingBreeding between close relatives.

This causes the gradual increase in homozygosity.

Example:

In most species, related individuals share about 80% of the same genes.

With cheetahs, this figure rises to approximately 99%.

The genetic inbreeding in cheetahs has led to low survivorship (a large number of animals dying), poor sperm quality, and greater susceptibility to disease.

More on the Bottleneck Effect• From an original large population, only few

survive to repopulate the habitat.• The few survivors are likely to have a

genetic structure (a set of genotype frequencies) that is unrepresentative of the ancestral large population

Example of a genetic bottleneck

Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s.

Hunting reduced their population size to as few as 20 individuals at the end of the 19th century.

Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted

Comparing the 2 Effects:

Founder Effect is sampling error as a result of movement of a few individuals away from the main population

Bottleneck Effect is sampling error as a result of only a few individuals surviving a population crash.

What’s inbreeding depression?

The fertility and survival are reduced compared with populations that are not inbred. Caused by an increase in homogeneity.

Outbreeding enhancement/hybrid vigor is when they manage a species and bring back heterogeneity.

In the adder case, introducing snakes from other populations

Ex.

a population of 40 adders experienced inbreeding depression when farming activities in Sweden isolated them from other adder populations.

Higher proportions of stillborn and deformed offspring were born in the isolated population than in the larger populations

Artificial Selection• Much of what Darwin

learned about Natural Selection, came from his observations about selectively breeding crops and domestic animals.

• This showed that continued selection was powerful enough to bring about large-scale changes within a species.

A change in plant or animal population by selective breeding

Fitness• The suitability of an

organism to a given environment

• This is often measured by the number of offspring that an individual has

• However, the offspring must survive to contribute to the following generation

•Consider two zebras:• Both live in the savannah and must escape predation by lions while also finding food & water. As babies, they were protected by the herd

•Zebra 1- has a deformed rear leg•Zebra 2- is fast and strong

• Soon after they both became juveniles, a lion pride attacked the heard. – Zebra one, not being able to

run fast, was caught by the lion pride.

– Zebra 2 escaped this, and many more attacks. Lived to have many offspring who were also fast and strong runners.

– So Zebra 2 was more fit than Zebra 1, by surviving.

Adaptations that affect Fitness• Camouflage-

– color is not necessarily relevant

– Pattern and shades matter

– Pattern breaks up an organism’s outline

• Protective Coloration- – Color of animal blends in with

environment

– However, this can Allows the organism’s shadow to reveal the outline

Camouflage and Protective Coloration: A Model of Natural Selection

• Natural selection operates on the principle of “survival of the fittest”.

• Fitness can be defined as the suitability of an organism to a given environment.

• One might ask if one set of features favorable in one environment might prove unfavorable in another environment.

• In this lab you will test the following hypothesis: – If survival is related to specific characteristics in a given environment,

then altering the environment will decrease the survival rate.

• Once you have formed a conclusion to this hypothesis and how it relates to the adaptations of camouflage and protective coloration, you will apply this information to the peppered moths of Manchester, England. You will predict the direction of an adaptive shift and the resulting gene

frequencies.

Chapter 17

Origins of Life

Origins of Life• Astrobiology is study of the

origin, evolution, distribution, & destiny of life in the universe.

• It attempts to answer 3 fundamental questions:– How did (does) life begin

and develop?– Does life exist elsewhere in

the universe?– What is life's future on

Earth and beyond? Advances in the biological sciences, space exploration, and astronomy make it possible for us to realistically attempt to answer them.

• We know that free oxygen probably was not present in the early atmosphere. – Compounds in early rocks do not contain oxygen……

significant amounts of oxygen would not have formed until the process of photosynthesis was under way.

• Some of the ideas about the origin of life cannot be stated in the form of hypotheses or tests; – therefore, science is limited in it’s ability to investigate such

ideas.

• RNA is a more likely candidate for life formation that DNA because DNA is more complex than RNA and requires proteins for its replication. – RNA can cataylze its own splicing.

• The conditions on early Earth were probably similar to those on Venus and Mars, – that is, containing high levels of CO2, water vapor, and N2 and small

amounts of H2.

• The formation of organic compounds necessary for life is better understood than the formation of the first cells.

• Chemical evolution provides a mechanism by which life could have originated from the development of increasingly more complex chemicals in the primitive seas. – Darwinian evolution provides a means by which organisms can

change over time and could not start until chemical evolution resulted in the first life.

• We know that one characteristic of living things is their need for energy. – Early energy sources included lightning, UV radiation, and heat from

the radioactive decay within earth. – These energy sources drove the chemical reactions that produced

the first life. – Those organisms most efficient at using the energy had an

advantage over less efficient organisms.

Heterotroph Hypothesis• In the 1920’s, Oparin and Haldane

– hypothesized that the early atmosphere had methane, ammonia, hydrogen, and water vapor in it.

– An energy source (radioactivity, lightening, cosmic radiation, and/or heat from volcanoes) reacted with those gases and formed organic compounds.

• This hypothesis requires 3 major steps:– Nonbiolobical processes had to supply

some organic molecules.– Some process had to trigger the small

molecules to form polymers like nucleic acids and proteins

– Some other processes had to organize the polymers that could replicate itself.

Urey & Miller’s Experiment- 1952

• Can organic compounds be generated under conditions similar to those that existed on primeval earth?

Conclusions:

The organic building blocks of life (amino acids and all the building blocks for nucleic acids) formed in the liquid.

Early Organisms

• Because the early atmosphere lacked oxygen gas- the first organisms must have been anaerobic (probably methanogens)

• There is some evidence of photoautotrophs dating back to 4 billion years ago.

• The level of oxygen gas was probably insignificant until about 2 billion years ago.

• Aerobic respiration may have evolved as a way to produce large amounts of ATP from food sources.

Endosymbiotic Hypothesis

• The first microfossils of eukaryotes are about 1.4 billion years old.

• This hypothesis proposes that eukaryotes originated from a symbiotic relationship between large anaerobic prokaryotes and smaller aerobic or photosynthetic prokaryotes

• The question of whether life was created by a supernatural being cannot be investigated by the methods of science because no controlled experiments can be set up and run.

Chapter 18

Diversity and Variation

Natural Selection:• Not all members of a population

necessarily have an equal chance of surviving and reproducing.

• Some individuals are better adapted to their environment than are others.

• The better adapted individuals are more "fit" and tend to survive and reproduce, passing on their adaptations to the next generation in greater frequency than those adaptations of the less "fit" members of the population

How does natural selection shape a population? • First, let’s make sure we understand variation and

bell shaped curves:

– In a bell curve, what does the y-axis represent?

• The number of individuals

– In a bell curve, what does the x-axis represent?

• the value of a particular characteristic– could be size, color, etc.

– What does it mean when a variable exhibits continuous variation?

• It has a wide range over which it varies, like human height

Directional Selection

• tends to favor phenotypes at one extreme of the range of variation.

The graph shows the decrease in size of pink salmon caught in two rivers in British Columbia since 1950, driven by selective fishing for the large

individuals.

Stabilizing Selection:• Organisms with extreme characteristics die or fail

to reproduce, resulting in populations of individuals that possess intermediate characteristics.

•Infants weighing significantly less or more than 7.5 pounds have higher rates of infant mortality. Selection works against both extremes.

Disruptive Selection

• favors individuals at both extremes of variation: selection is against the middle of the curve

What’s taxonomy? The theories and techniques of describing, grouping and naming organisms •Biologists do not think of species simply as a long alphabetical list. •Since Linnaeus, the father of modern taxonomy, species have been arranged in a taxonomic hierarchy: •Species are grouped in genera.

•The gray wolf species Canis lupus and the golden jackal Canis aureus , for example, are grouped in the genus Canis .

•Genera are grouped into families; •the genus containing dogs and wolves combines with several other genera, such as the fox genus Vulpes , to make up the family Canidae.

•Several families combine to make up an Order• Carnivora, in this example.

•Orders make a Class (Mammalia).

• Classes make a Phylum (Chordata).

• Phyla make up one of the five Kingdoms (Animalia).

Why do we classify organisms?

•In order to make sense of the diversity of organisms, similar organisms together and it is necessary to group organize these groups in a non-overlapping hierarchical arrangement.•Morphological, physiological, metabolic, ecological, genetic, and molecular characteristics are all useful in taxonomy because they reflect the organization and activity of the genome. •Nucleic acid structure is probably the best indicator of relatedness because nucleic acids are either the genetic material itself or the products of gene transcription.

Why else is classification important?

Practical and scientific reason—

•identifying wild relatives of crops– that provide breeders with useful alleles

•Benefits to public health--disease control

•Identifying unknown species that might help understand ecosystems

•Understanding the “unity of life”

"Of all the categories in this classification system, only the lowest level, the species, is objective; that is, biologists can test whether two different populations of individuals represent two different species by testing whether they can interbreed successfully in nature. (p. 434, Postlethwait & Hopson, 1995)

What’s a Species?The basic taxonomic group is the species

All individuals and populations of a particular type of organism that can interbreed with one another.

Species may look different, but as long as they can produce FERTILE offspring they are still members of the same species.

The Species Concept

Species remain separate from one another in three basic ways:

• potential mates do not meet;

•potential mates meet but do not breed

•potential mates meet and breed but do not produce fertile or viable offspring.

Species are interbreeding natural populations which are reproductively isolated from other such groups.

Appearance Isn’t Everything

•Organisms may appear to be alike and be different species.

•For example, Western meadowlarks (Sturnella neglecta) and Eastern meadowlarks (Sturnella magna) look almost identical to one another, yet do not interbreed with each other

•Thus, they are separate species according to this definition.

Evidence Used to Classify Organisms

• morphology• anatomy /development• the fossil record• molecular data

Placing Organisms in Groups

Ex. All animals with hair who give birth to live young are classified as mammals

Using Homologous Structures

Similarities of biological structures that results from evolution form a common ancestor.

Forearm of frogs, lizards, birds, humans, cats, etc.

Homologous structures are are also those that develop from similar embryological origins

Adult fish, salamanders, turtles, chickens, rabbits, and humans bear virtually no resemblance to one another.

Yet these animals are virtually indistinguishable as embryos.

Can you pick out which one is the human?

How about now?

Which one is the human embryo?

Why should animals that have markedly different adult forms and function develop from such similar embryos?

Far back in vertebrate history, they all had a common ancestor, probably some type of primitive fish, that developed from a similar type of embryo.

As the various types of vertebrates evolved, they each retained this basic vertebrate embryo as part of their life cycle– even though its parts gave rise to different adult organs.

Analogous Structures Similarities in form or function that are not a result of evolution from a common ancestor, but is evidence of convergent evolution (similar environmental pressures).

Ex. wings of insect, bird, bat and pterosaur

Analogous vs. Homologous Structures

Chemical homologies

•Since characteristics of an organism are determined by its genetic content, changes in organism over the course of evolution are reflected in changes in the nucleotide sequence.

•The longer the period since two species have diverged from a common ancestor, the greater the number of substitutions that are found in corresponding genes and proteins between the species.

Ex. The sequence of amino acids in a protein molecule or of nucleotides in DNA.

The Linnean classification system

The system uses homologies to group species into larger and more general categories. Kingdom, phylum, class, order, family, genus, species

Binomial nomenclature?

The scientific naming of species whereby each species receives a Latin or Latinized name of two parts

• the first indicating the genus and the second being the specific epithet.

•For example, Juglans regia is the English walnut; Juglans nigra, the black walnut.

How do you write a scientific name?

•Capitalize genus

•underline/italicize both names

•lower case species name

Ex.

American Black Bear- Ursus americanus

Brown Bear- Ursus arctos

•Subspecies Syrian (Brown) Bear (Ursus arctos syriacus)

•Subspecies Grizzly Bear, (Ursus arctos horribilis)

•Subspecies Kodiak Bear, (Ursus arctos middendorffi)

Ways to Classify Organisms

Current classification systems attempt to reflect the evolutionary relationships of organisms

Orthodox-

• Originally, organisms classified using the Linnaean system were grouped together based simply on physical similarities

•Ex. Dividing birds into orders based on their beaks and claws

• This method can be subjective

Phenetic principle of classification

•groups species according to their observable phenetic attributes

• if two species look more like each other than either does to any other species, they will be grouped together.

•Ex. a wolf and a dog (same genus) look phenetically more alike than do a wolf and a dolphin which are in the same Class (mammalia).

•NOTE: Nothing needs to be known about evolution in order for species to be classified phenetically.

Phylogenetic principle of

classification •Only entities that have evolutionary relations can be classified in this way

• It classifies species according to how recently they share a common ancestor.

•Two species that share a more recent common ancestor will be put in a group at a lower level than two species sharing a more distant common ancestor

For instance the wolf and the dog opposite share a more recent common ancestor than do a wolf and a dolphin: they are therefore both classified in the genus Canis.

The phylogenetic principle is the basis behind the taxonomic school called cladistics.

Cladistics•Assumes each group has an ancestor that other species do not share

•Group species according to ancestry and homologous characteristics.

Ex. All mammal species have mammary glands, but no other organism do.

•Therefore all mammals must be descended from a species that has no other living descendants.

•Mammals form a clade, or branch on this diagram of the history of the animals.

•One way to discover how groups of organisms are related to each other (phylogeny) is to compare the anatomical structures of many different organisms.•Recall, corresponding organs and other body parts that are alike in basic structure and origin are said to be homologous structures

•for example, the front legs of a horse, wings of a bird, flippers of a whale, and the arms of a person are all homologous to each other.•When different organisms share a large number of homologous structures, it is considered strong evidence that they are related to each other.

Making a Cladogram

SETS TRAITS Tuna Horse Human#1 Backbone

#2 Placenta

#3 Foramen magnum fwd. (large opening at base of skull)

TOTALS of X’s

x x

x

x

x

x

1 2 3

Step 1: determine which of the characteristics each animal has. Step 2: Draw a cladogram to illustrate the ancestry of these animals. The diagram should reflect shared characteristics as time proceeds.

Notice how the different animals are all at the same time level (across the top) since they all live today.

Practice making a cladogram

Vestigial Structures

•Why do whales have underdeveloped pelvis and leg bones?

•What’s up with the diminished toe bones in horses?

•What about our appendix? Wisdom teeth? Tail in embryos?

These are remains of ancestral structures or organs which were, at one time, useful.

Chapter 19

Changes in Species

SpeciationQ: When are two populations new species? A: When populations no longer interbreed

they are thought to be separate species.

•As natural selection proceeds, populations occupying different environments will diverge into races, subspecies, and finally separate species.

•Barriers to gene flow between populations isolate those populations, ultimately leading to the formation of new and separate species

Reproductive Isolating Mechanisms•Pre-zygotic Isolating Mechanisms- these act before fertilization can

happen -Ecological:

-Different habitats»Example Lions and Tigers–Geographical:

–Mountains, islands, or rivers separate»Chipmunks in the Grand Canyon

–Seasonal: –Different breeding season

»Blue whales in northern and southern hemisphere–Mechanical:

–Parts don’t fit»bushbabies

–Behavioral: –Different mating behavior

»crickets

Post-zygotic Isolating Mechanisms-

Gametic incompatibility

Sperm transfer takes place, but egg is not fertilized.

Zygotic mortality Egg is fertilized, but zygote does not develop. Hybrid inviability

Hybrid embryo forms, but of reduced viability.

Hybrid sterility Hybrid is viable, but resulting adult is

sterile. Hybrid breakdown

First generation (F1) hybrids are viable and fertile, but further hybrid generations (F2 and backcrosses) may be inviable or sterile.

•these happen, even if fertilization happens

Paths of Speciation:

• Allopatric Speciation

– Populations begin to diverge when gene flow between them is restricted.– Geographic isolation is often the first step in allopatric speciation.

Parapatric Speciation- • The splitting of a population into 2 species

under conditions where members of each population reside in adjacent areas

Sympatric Speciation• No Geographic isolation• Refers to the formation of two or more descendant species from a

single ancestral species all occupying the same geographic location.• Most common in Plants- failure to reduce chromosome number

results in polyploid plants that reproduce successfully only with other polyploids.

• Some scientists don't believe that it ever occurs-- they feel that interbreeding would soon eliminate any genetic differences that might appear.

animation

Hybridization• Two species mate and make a hybrid

that cannot mate with either parent.

Patterns of Evolution:

• Divergent Evolution- two species evolve from a common ancestor and become different over time.

                  

                                  

• Convergent Evolution- species with different ancestors colonize similar habitats with a superficial resemblance

Comparing Patterns of Evolution:

Convergent evolution takes place when species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure

Parallel evolution occurs when two species evolve independently of each other, but maintain the same level of similarity. Parallel evolution usually occurs between unrelated species that do not occupy the same or similar niches in a given habitat.

When people hear the word "evolution," they usually think of divergent evolution, the pattern where two species gradually become increasingly different.

• Adaptive Radiation- many species evolve from a single ancestral line- this is an example of a divergent evolutionary pattern

ExtinctionExtinction occurs when the population cannot adapt to changing environmental conditions.

The golden toad of Costa The golden toad of Costa Rica’s Monteverde cloud Rica’s Monteverde cloud forest became forest became extinctextinct because of climate because of climate change.change.

video

Pace of Evolution• Gradualism-

– Very gradually, over a long time, a population changes. – Over a short period of time it is hard to notice. – Change is slow, constant, and consistent.– The steady uninterrupted process has small adaptive steps– Darwin’s view

• Punctuated Equilibrium-• change comes in spurts. There is a period of very little change, and then one or a few huge changes occur• Often due to major changes in the environment.• Gaps in the fossil record

Coevolution• a change in the genetic composition of one

species (or group) in response to a genetic change in another. – a.k.a. “reciprocal evolutionary change” in

interacting speciesEx.

Central American Acacia species have hollow thorns and pores at the bases of their leaves that secrete nectar.

These hollow thorns are the exclusive nest-site of some species of ant that drink the nectar.

But the ants are not just taking advantage of the plant—they also defend their acacia plant against herbivores.

Pollination

• For pollination to be effective, a relationship must be established between the pollinator and the blossom to be pollinated, involving:– The pollinator should visit this particular blossom regularly and get a

reward such as nectar for pollinating the plant. – The plant must supply:

• Some kind of reward (food?) for the pollinator (nectar, pollen) • Some kind of attractant to advertise the presence of the reward

This could be a direct attractant such as odor, color, shape, or texture• A means of putting pollen onto the pollinator such that it is effectively

transferred to the next flower visited.

Examples•The common snapdragons that many people plant in their gardens are designed for a bumblebee of just the right weight to trip the opening mechanism.

•Moth-pollinated plants often have spurs or tubes the exact length of a certain moth’s “tongue.”

The Arms Race

• Murex snails, have evolved thick shells and spines to avoid being eaten by animals such as crabs and fish.

• These predators have, in turn, evolved powerful claws and jaws that compensate for the snails’ thick shells and spines.

                                 

         

                                            

Predator/prey coevolution can lead to an evolutionary arms race.

Evolution of Antibiotic Resistance:

• Forty or fifty years ago, thanks to antibiotics, scientists thought medicine had all but eradicated infectious agents as a major health threat.

• More recently, an upsurge of infectious disease is a problem we have unwittingly created for ourselves b/c:– rapid, frequent, and relatively cheap international travel

allows diseases to leap from continent to continent – Many people have inadequate sanitation and lack of

clean drinking water – We have overused the "miracle drugs“ to treat such

diseases to the point that they lose their potency

• Whenever antibiotics wage war on microorganisms, a few of the enemy are able to survive the drug.

• Because microbes are always mutating, some random mutation eventually will protect against the drug.

• Antibiotics used only when needed and as directed usually overwhelm the bugs.

• Too much antibiotic use selects for more resistant mutants.

• When patients cut short the full course of drugs, the resistant strains have a chance to multiply and spread.

Animals and Antibiotic Resistance• As much as 70% of the

antibiotics produced in the United States today are for use in food animals

• In addition to treating disease, a lot of these drugs are given to healthy animals to prevent illness and to promote growth. – Small farms are giving way to

huge consolidated feedlots that facilitate the rapid spread of bacteria and disease. Feedlots housing up to 100,000 cows*

•The economic equation. Livestock breeders say that reducing the use of antibiotics in animals will significantly impact the cost of meat, though environmentalists and others say the cost of antibiotic resistance would be far greater.

* In 1945, the typical henhouse contained 500 birds. Today, the average ranges from 80,000 to 175,000. In 1980, there were 650,000 hog farms in the United States. In 2001, there were 81,000, including Circle Four Farms in Milford, Utah, a mega-facility housing 500,000 hogs in a 35-square-mile area, according to the U.S. Department of Agriculture

The End

Richard Owen

• Born in England• Trained as a surgeon• Catalogued 13,000 human and animal anatomical

specimens• Became a lecturer in comparative anatomy• Worked with Darwin to catalogue the fossils he returned

with from the S.S. Beagle– However, he became outspokenly oppositional towards Darwin’s

theory of Natural Selection

• He believed there must exist a common structural plan for all vertebrates – but this was the idea of a Divide mind, not an archetype

Thomas Henry Huxley

• Born in England• Very little formal schooling• Navy officer turned surgical apprentice• Darwin’s Bulldog

– A passionate defender of Darwin’s theory of Natural Selection– During the debate with Archbishop Wilberforce who ridiculed

evolution he was asked whether he was descended from an ape on his grandmother's side or his grandfather's

– He responded by saying, "I would rather be the offspring of two apes than be a man and afraid to face the truth."

• He also wrote essays on theology and philosophy from an "agnostic" viewpoint