Evolution Chapters 22, 23, 24, 26 - PowerPoint Presentation

Slide1

Evolution

Chapters 22, 23, 24, 26

Slide2

Chapter 22 – Descent with Modification

Slide3

The Era of Evolutionary Biology

On November 24, 1859,

Charles Darwin

published his hypothesis in On the Origin of Species by Means of Natural Selection, ushering in the era of evolutionary biology.Darwin defined evolution as descent with modification, proposing that Earth’s many species are descendants of ancestral species that were very different from those alive today.Evolution can also be defined more narrowly as a change in the genetic composition of a population over time.

This idea of changing species over time was the opposite of Greek philosopher

Aristotle (384-322AD) who opposed any concept of evolution and viewed species as fixed and unchanging. Most people at the time agreed with Aristotle’s idea.

Slide4

Carolus

Linnaeus

Linnaeus

was a Swedish physician and botanist and did a lot of work for the field of

taxonomy

. He came up with binominal nomenclature which is a system of naming organisms based on their common anatomy and morphology. In this system, the genus and specie is the organisms scientific name. This process was utilized by Darwin and is still used today.

Slide5

Georges Cuvier

Cuvier was a French anatomist who really started the branch of science we know now as

paleontology

(study of fossils). He did a lot of work in the Paris Basin and noticed that the deeper the fossils were, the more dissimilar they were from modern life. He did not believe in evolution, and instead, explained the differences with the theory of

catastrophism. He hypothesized that there had to be some type of catastrophe (flood, fire, etc) between each group of organisms. Darwin’s views were influenced by fossils, remains or traces of organisms from the past mineralized in sedimentary rocks.

Fossils within layers of sedimentary rock show that a succession of organisms have populated Earth throughout time.

Paleontology

, the study of fossils, was largely developed by

Georges

Cuvier

(1769–1832).

Slide6

James Hutton

James Hutton

proposed the idea of

Gradualism

. This is the theory that the Earth’s geological features are due to slow but continuous processes, and that what we see is an accumulation of these gradual change. This was in contrast to Cuvier’s theory of catastrophism. Darwin was heavily influenced by Hutton’s gradualism theory.

Slide7

Charles Lyell

Lyell

(1797-1875) was the main geologist of Darwin’s time and he studied Hutton’s gradualism theory to come up with an idea of his own called

uniformitarianism

. This word refers to the notion that the geological processes have not changed through history. The forces that made the mountains and the forces that eroded the mountains are still working at the same rate today as they did many years ago in history.

Both Hutton’s and Lyell’s observations and theories had a strong influence on Darwin. If geologic changes result from slow, continuous processes rather than sudden events, then the Earth must be far older

than the few thousand estimated by theologians from biblical inference

.

Slide8

Jean

Baptiste

Lamarck

Lamarck came up with the

use/disuse theory. This is the idea that the parts of your body you use more become stronger and better (this is correct!). He also hypothesized (incorrectly) that these inherited traits can be passed onto offspring.

A classic example is the long neck of the giraffe. Lamarck reasoned that the long, muscular neck of the modern giraffe evolved over many generations as the ancestors of giraffes reached for leaves on higher branches and passed this characteristic on to their offspring

Slide9

Charles

Darwin

He came up with the theory of evolution and natural selection as its mechanism.

RECALL

: Before Darwin, people thought

the Earth was 6000 years old and unchanging.

Slide10

The Earth was very old (up till this point they thought it was only 6000 years old)

Natural selection was the mechanism of evolution

Species evolve and change over time

More facts about DarwinHe was a naturalist who worked as a clergyman. His father sent him to medical but he dropped out. Most scientists and naturalists were in the clergy at this time.

He sailed around the world on a boat named the Beagle when was hired as a naturalist and a conversational companion to the captain. While on the Beagle, he did lots of research on Finches in the Galapagos Islands. He published his theories about evolution and natural selection in a book called On the Origin of Species

He used Linnaeus’ ideas about taxonomy to classify organisms based on their commonalities

Darwin’s Ideas…

Slide11

The Voyage of the Beagle

Darwin

embarked from England on the Beagle in December 1831.

Darwin collected thousands of specimens and noted that the plants and animals of South America were very different from those of Europe. Darwin also found fossils that were formed by earthquakes similar to one he experienced.These observations reinforced Darwin’s acceptance of Lyell’s ideas and led him to doubt the traditional view of a young and static Earth.Darwin’s interest in the geographic distribution of species was further stimulated by the Beagle’s visit to the

Galápagos Islands, a group of young volcanic islands 900 km west of the South American coast.

Slide12

Adaptations and Natural Selection

-

During

his travels, Darwin observed many examples of adaptations, characteristics of organisms that enhance their survival and reproduction in specific environments (ex. finches and differences in beaks related to food they ate). - Darwin explained that adaptations arise by natural selection, a process in which individuals with certain inherited characteristics leave more offspring than individuals with other characteristics.- By

the early 1840s, Darwin had developed the major features of his theory of natural selection as the mechanism for evolution.

Slide13

Natural Selection

Natural Selection

is the survival of the fittest. The organisms best suited for the environment will survive longer and produce more offspring so that many copies of their “favorable” genes are passed on to the next generation.

Keep in mind that Natural

Selection is an editing mechanism, not a creative force. It can act only on existing variation

in the population; it cannot create favorable traits, it selects for favorable traits that are already present in the population.Also, Natural Selection favors traits that increase fitness in the current, local environment. What is adaptive in one situation is not adaptive in another.

Slide14

Alfred Wallace

In

June 1858,

Alfred Russel Wallace (1823–1913), a young naturalist sent Darwin a manuscript containing a hypothesis of natural selection essentially identical to Darwin’s. Darwin finished The Origin of Species and published it the next year.

Although both Darwin and Wallace developed similar ideas independently, the theory of evolution by natural selection is attributed to Darwin because he developed his ideas earlier and supported the theory much more extensively.

Slide15

The Origin of Species

Darwin used the phrase

descent with modification

to describe evolution.All organisms are related through descent from a common ancestor that lived in the remote past. As a result, organisms share many characteristics, explaining the unity of life.Over evolutionary time, the descendants of that common ancestor have accumulated diverse modifications, or adaptations, that allow them to survive and reproduce in specific habitats.Over long periods of time, descent with modification has led to the rich diversity of life we see today.

Slide16

Natural Selection/ Artificial Selection

Darwin proposed a mechanism

—

natural selection —to explain the observable patterns of evolution.Darwin’s views on the role of environmental factors in the screening of heritable variation were heavily influenced by artificial selection.Today, we use artificial selection all the time when breeding plants and animals. Darwin described two observations of nature, from which he drew two inferences.Observation #1: Members of a population vary greatly in their inherited traits.

Observation #2: All species are capable of producing more offspring than the environment can support, and many of these offspring fail to survive and reproduce. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment than other individuals tend to leave more offspring than other individuals.Inference #2

: This unequal ability of individuals to survive and reproduce will cause favorable traits to accumulate over generations.

Slide17

Thomas Malthus

Malthus did a lot of work with

population studies

. His main conclusion was that populations grow faster and will eventually out-grow their resources. Darwin was especially interested in his theory on “over-reproduction”.

Malthus contended that much human suffering—disease, famine, war—was the inescapable consequence of the potential for human populations to increase faster than food supplies and other resources (over-reproduction is characteristic of most species.)

NOTE  the smallest unit that can evolve is a POPULATION…individuals do not evolve!

Slide18

Evolution THROUGH Natural Selection

3 Important Points!

Although natural selection occurs through interactions between individual organisms and their environment,

individuals do not evolve. A population is the smallest group that can evolve over time.Natural selection can act only on heritable traits, traits that are passed from organisms to their offspring. Characteristics acquired by an organism during its lifetime may enhance its survival and reproductive success, but there is no evidence that such characteristics can be inherited by offspring.

Environmental factors vary from place to place and from time to time. A trait that is favorable in one environment may be useless or even detrimental in another environment.

Slide19

Direct Evidence that points to Evolution

There are 4 types of evidence that point to evolution:

1. Direct Observations of Evolution

2. Homologies3. Fossil Record4. Biogeographies

Slide20

Direct Observations of Evolution

One example of seeing evolution is by looking at antibiotic- resistant bacteria. Let’s look at the evolution of MRSA:

In

1943, penicillin became the first widely used antibiotic. By 1945, more than 20% of S. aureus in hospitals were already resistant to penicillin.  Researchers developed antibiotics that were not destroyed by penicillinase (an enzyme in the bacteria), but some S. aureus populations developed resistance to each new drug within a few years.In 1959, doctors began using the powerful antibiotic methicillin, but within two years

, methicillin-resistant strains of S. aureus appeared. Some individual bacteria were able to synthesize their cell walls using a different protein that was not affected by methicillin. These individuals survived the methicillin treatments and reproduced at higher rates than did other individuals.

Over time, these resistant individuals became increasingly common, leading to the spread of MRSA.

Slide21

Homologous and Analogous Structures

Homologous Structures

– similar features resulting from

common ancestry; Ex. Forelimbs of humans, cats, whales and bats

Analogous Structures

– similarities due to the same ecological role, but different evolutionary branches, so INDEPENDENT evolution of similar structures; Ex. Bat wing, bird wing

Slide22

Embryological Homologies

These are similarities that are seen when comparing the

embryos

of several different species. These homologies are

NOT present in the adult forms. This is a strong piece of evidence for evolution.

Slide23

Vestigial structures

Vestigial structures

are structures that once may have had important functions in our ancestors, but no longer are necessary. Some of the most interesting homologies are seen in vestigial structures.

Examples

-1. pelvic bones in snakes2. hip/ leg bones in whales3.

humans – ear wiggling muscles, wisdom teeth, appendix

Slide24

Fossil Record

This is a record of when organisms lived in history. Depending on what level of rock the fossils, one can discern when the organism lived. Also, the fossils give hints about the organisms anatomical structure.

The fossil record suggests that prokaryotes came first, then fishes, vertebrates, amphibians

, reptiles,

then mammals and birds.

Slide25

Biogeography

Evidence for evolution also comes from

biogeography

, the geographic distribution of species. The geographic distribution of organisms is influenced by many factors, including continental drift.We can also use our understanding of evolution to explain biogeographic data. For example, islands generally have endemic species

that are found nowhere else on Earth.Most island species are closely related to species from the nearest mainland or a neighboring island, reflecting the pattern of colonization of the island

Slide26

Chapter 23 – The Evolution of Populations

Slide27

POPULATIONS evolve, not individuals

Natural selection does act on

individuals.

Each individual’s traits affect its survival and its reproductive success relative to other individuals in the population.The evolutionary impact of natural selection is apparent only in the changes in a population of organisms over time and so it is the population, not the individual, which evolves.

Slide28

Microevolution

Microevolution

is defined as a change in allele frequencies in a population over time.Three mechanisms can cause allele frequencies to change: natural selection, genetic drift (chance events that alter allele frequencies), and gene flow (the transfer of alleles between populations).

Slide29

Variation within a Population

Quantitative Characters

→ vary along a continuum; have an additive effect; polygenic; Ex. skin color

Discrete Characters

→ Either/ or effect…you have it or you don’t – no middle ground

Polymorphism  2 or more forms of a discrete

variable (ex. ABO blood groups, dimples vs. no dimples)

(ADD POLYMORPHISM TO YOUR NOTES!!)

Individual variation occurs in all species and often reflects

genetic variation

, differences among individuals in the composition of their genes or other DNA segments

Slide30

Geographic Variation

Species also exhibit

geographic variation

, differences in the genetic composition of geographically separate populations.Clines → an example of geographic variation; graded change in a trait based on location

Example 1: As the latitude increases, the body fat % in birds increasesExample 2: As the altitude gets higher, the plant height gets shorter

Slide31

Mutations and Neutral Variation

The

genetic variation on which evolution depends originates when mutation, gene duplication, or other processes produce new alleles and new genes.

New alleles can arise by mutation, a change in the nucleotide sequence of an organism’s DNA.Some genetic variation in populations represents neutral variation  no phenotype gives an advantage or disadvantage (

example: fingerprints, bloodtype, attached vs. free earlobes, widow’s peak, eye color)

Slide32

Diploidy

and Sexual Reproduction

The tendency for natural selection to reduce variation is countered by mechanisms that

preserve or restore variation, including diploidy and balanced polymorphisms.Diploidy, having two copies of each chromosome, in eukaryotes prevents the elimination of recessive alleles via selection because recessive alleles do not affect the phenotype in heterozygotes.

Even recessive alleles that are unfavorable can persist in a population by “hiding” in heterozygous individuals.Heterozygote protection maintains a huge pool of alleles that may not be suitable under the present conditions but may become beneficial when the environment changes. (balanced polymorphism)

Sexual reproduction also increases variety via: crossing over, independent assortment and random fertilization.

Slide33

Hardy- Weinberg Theorem

The HW Theorem tests whether or not an population is EVOLVING

. This theory says that the frequency of alleles in a populations gene pool

remains constant over generations

. Think of the analogy that a deck of cards keeps getting shuffled, but there is always the same number of kings, queens, jacks, etc. If the allele frequencies do NOT remain the same, that means the population is EVOLVING

. p2 + 2pq + q2 = 1

p + q = 1

p

= frequency of DOMINANT allele

q

= frequency of RECESSIVE allele

Population



is a group of individuals of the same species that live in the same area and interbreed to produce fertile

offspring

Gene

Pool



t

he

total of all the alleles for all of the loci for all of the individuals in a

population

5 Assumptions of HW

:

1. Large population size

2. No migration

3. No net mutations

4. Random mating

5. No natural selection

So…because of all these assumptions, we

do not expect

a

natural population

to demonstrate HW…the differences result in EVOLUTION!

Slide34

Examples of HW

For example, imagine a population of

500 wildflower plants

with two alleles (CR and CW) at a locus that codes for flower pigment.Suppose that in the imaginary population of 500 plants, 20 (4%) are homozygous for the CW allele

(CWCW) and have white flowers.Of the remaining plants, 320 (64%)

are homozygous for the CR allele (CRCR) and have red flowers.These alleles show

incomplete dominance

,

so

160 (32%)

of the plants are

heterozygous

(C

R

C

W

) and produce

pink flowers

.

Because these plants are diploid, the

population of 500 plants has 1,000 copies of the gene for flower color

.

The

dominant allele (C

R

)

accounts for 800 copies (320 × 2 for C

R

C

R

+ 160 × 1 for C

R

C

W

)



640 + 160 =

800

.

The

frequency

of the

C

R

allele

in the gene pool of this population is

800/1,000

=

0.8, or 80%.

The C

W

allele must have a

frequency

of

1.0 − 0.8 = 0.2, or 20%.

When there are two alleles at a locus, the convention is to use

p

to represent the frequency of one allele and

q

to represent the frequency of the other.

Thus

p

, the frequency of the C

R

allele in this population, is

0.8

.

(typically p is DOMINANT)

The frequency of the C

W

allele, represented by

q

, is

0.2

. (typically q is RECESSIVE)

Allele and genotype frequencies can be used to test whether evolution is occurring in a population.

p + q = 1

Slide35

Assumptions of Hardy Weinberg

No net mutations

.

The gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated. Random mating. If individuals pick mates with certain genotypes, or if inbreeding is common, the mixing of gametes will not be random and genotype frequencies will change.No natural selection. Differential survival or reproductive success among genotypes will alter allele frequencies.Extremely large population size. In small populations, chance fluctuations in the gene pool will cause allele frequencies to change over time, a process called genetic drift.

No gene flow. Gene flow, the transfer of alleles due to the migration of individuals or gametes between populations, will change the frequencies of alleles.

A population must satisfy all five conditions to remain in Hardy-Weinberg equilibrium.

Hardy-Weinberg explains NON-EVOLVING populations! If one or more of these 5 conditions ARE NOT met, then that means the population is

EVOLVING!

Slide36

Applying HW to a Human Population

We can use the Hardy-Weinberg principle to estimate the percent of the human population that carries the allele for the inherited disease phenylketonuria (PKU).

From

the data, we know that the frequency of homozygous recessive individuals (q2 in the Hardy-Weinberg principle) is one in 10,000, or 0.0001.The frequency of the recessive allele (

q) is the square root of 0.0001 = 0.01.The frequency of the dominant allele (p

) is p = 1 − q, or 1 − 0.01 = 0.99.The frequency of

carriers

(heterozygous individuals) is

2

pq

= 2 × 0.99 × 0.01 = 0.0198, or about 2%.

Thus, about 2% of the U.S. population carries the PKU allele.

p

2

+ 2pq + q

2

= 1

Slide37

Hardy-Weinberg Practice Problems

PROBLEM #1



In a population of flowers, 36% are white. White flowers are homozygous recessive (aa). Red flowers are dominant. Calculate the frequency of the ‘a’ allele and the ‘A’ allele. Calculate the frequency of the genotypes AA and Aa. Calculate the frequency of white flowers vs. red flowers.

Slide38

ANSWER#1



In a population of flowers, 36% are white. White flowers are homozygous recessive (aa). Red flowers are dominant.

Calculate the frequency of the ‘a’ allele and the ‘A’ allele. .36 = q2 so q = .6  a = .6 ….so…. A = .4 (1-q = p)

Calculate the frequency of the genotypes AA and Aa. AA = p2 …so…(.4)2 =

.16 Aa = 2pq … so… 2(.4)(.6) = .48 Calculate the frequency of white flowers vs. red flowers. White flowers = q2

=

.36

Red flowers

= 2pq

+

p

2

= .48 + .16 =

.64

Slide39

PROBLEM #2



In AP Stat, there are 100 total students and 96% of the students did well on the test. The other 4% failed. If we pretend that these traits are genetic rather than environmental, and the four students that failed were of genotype aa, calculate the following:

Calculate the frequency of the ‘a’ allele and the ‘A’ allele.

Calculate the frequency of the genotypes aa, AA and Aa.

Slide40

ANSWER #2



In AP Stat, there are 100 total students and 96% of the students did well on the test. The other 4% failed. If we pretend that these traits are genetic rather than environmental, and the four students that failed were of genotype aa, calculate the following:

Calculate the frequency of the ‘a’ allele and the ‘A’ allele.

q

2

= .04 so q = .2



a = .2

1-q = p so p = .8 

A = .8

Calculate the frequency of the genotypes aa, AA and Aa.

aa =

.04

AA = p

2

= (.8)

2

=

.64

Aa = 2pq = 2(.8)(.2) =

.32

Slide41

PROBLEM #3



A population of randomly-mating lab mice contains 65% brown mice. Brown coloring is dominant to white. White mice are homozygous recessive. How many mice are heterozygous?

Slide42

ANSWER #3



A population of randomly-mating lab mice contains 65% brown mice. Brown coloring is dominant to white. White mice are homozygous recessive. How many mice are heterozygous?

Brown = 65% so….White = 35% (REMEMBER TO FIND Q FIRST!)

q2 = .35 so q = .59

p = 1-q so 1-.59 p = .41

Heterozygous = 2pq = 2(.41)(.59) = .48

so

48% of the total mice are heterozygous

.

Slide43

Natural Selection



RECALL

Individuals with variations better suited to the environment tend to produce more offspring than those with variations that are less well suited.As a result of selection, alleles are passed on to the next generation in frequencies different from their relative frequencies in the present population.By consistently favoring some alleles over others, natural selection can cause adaptive evolution  evolution

that results in a better match between organisms and their environment.

Slide44

Genetic Drift

Genetic Drift

is one of the main causes of microevolution (change in frequency of a populations alleles from generation to generation). If the sample size is too small (so this is especially for SMALL populations), a change will have a larger effect on the overall population. The

definition of genetic drift is a change in a populations allele frequency

DUE TO CHANCE. There are two situations…. Bottleneck effect and Founder effect.

There are FOUR key points about genetic drift: Genetic drift is significant in small populations.Genetic drift can cause allele frequencies to

change at

random

.

Genetic

drift can lead to a

loss of genetic variation

within

populations.

Genetic

drift can cause

harmful alleles to become fixed

.

Slide45

Founder Effect

→

When a small part of a population moves to a new locale, or when the population is reduced to a small size because of some environmental change, the genes of the "founders" of the new society are disproportionately frequent in the resulting population.

Bottleneck Effect

→

When the population undergoes a drastic reduction in size as a result of chance events(usually a disaster – tsunami, earthquake, etc); the genes of the survivors may not be representative of the original population

Slide46

Gene Flow

Gene flow

is the transfer of alleles among populations due to the migration of fertile individuals or gametes.Gene flow tends to reduce differences between populations.With increased human mobility, mating is more common between previously isolated populations, leading to an exchange of alleles and reducing genetic differences between human populations.

Slide47

Darwinian Fitness

Adaptive

advantage (organisms being better suited for the environment they are currently in)

can lead to greater relative fitness (aka “Darwinian Fitness”): the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals. SO…the more fertile offspring you leave in the next generation, the more “fit” you are.

Slide48

Types of Selection

Directional Selection

→ shifts the overall make up of the population by favoring variants of one extreme

Disruptive (Diversifying) Selection → favors variants of opposite extremesStabilizing Selection

→ favors intermediate variants; maintains status quo and decreases variation

Slide49

Sexual Dimorphism

Sexual Dimorphism

→ differences in size, shape and color between males and females of the same species

Intrasexual

Selection

→ direct competition for matesIntersexual Selection → individual of one sex are choosy in picking a mate

Slide50

Balanced Polymorphism

Balancing selection

occurs when natural selection maintains stable frequencies of two or more phenotypes in a population.One mechanism that produces balanced polymorphism is heterozygote advantage.In some situations, individuals who are heterozygous at a particular locus have greater fitness than homozygotes. (Ex. Individuals who are heterozygous for sickle cell anemia are also resistant to malaria)A second mechanism that promotes balanced polymorphism is frequency-dependent selection

.Frequency-dependent selection occurs when the fitness of any one morph declines if it becomes too common in the population.Frequency-dependent selection has been observed in a number of predator-prey interactions in the wild.

Slide51

Natural Selection CANNOT make PERFECT organisms

1.

Selection

can act only on existing variations  Natural selection favors only the fittest phenotypes among those currently in the population, which may not be the ideal traits; new advantageous alleles do not arise on demand.2. Evolution is limited by historical constraints

 Evolution does not scrap ancestral features and build new complex structures or behavior from scratch; evolution co-opts existing features and adapts them to new situations.3. Adaptations

are often compromises  Each organism must do many different things.Because the flippers of a seal must allow it to walk on land and also swim efficiently, their design is a compromise between these environments.Human limbs are flexible and allow versatile movements but are prone to injuries, such as sprains, torn ligaments, and dislocations, but better

structural reinforcement of human limbs would compromise their agility.

4.

Chance

, natural selection, and the environment

interact



Chance

events affect the subsequent evolutionary history of populations.

For example, the founders of new populations may not necessarily be the individuals best suited to the new environment, but rather those individuals that were carried there by chance.

Slide52

Chapter 24 – The Origin of Species

Slide53

Speciation

Speciation

→ origin of new species (when one specie splits into two or more species); can follow one of two patterns: Anagenesis

– transforms one species into anotherCladogenesis – build one NEW specie from a parent, but that parent specie also still exists

Speciation forms a conceptual bridge between microevolution, changes in allele frequencies within a population, and macroevolution, the broad pattern of evolution over

time.

Slide54

Biological Species Concept

This concept

defines a

species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but cannot produce viable, fertile offspring with other such groups.

Slide55

Reproductive Barriers

Prezygotic Barriers

→ barriers that prevent reproduction

BEFORE the gametes can come together to fertilize - Habitat Isolating  use different habitats so are unlikely to encounter each other to mate

- Behavioral

 different courtship behavior; sexes not attracted to each other - Temporal  mate at different times of the day/ year -

Mechanical

 anatomically incompatible so the sperm doesn’t get a chance to fertilize the egg

-

Gametic

 gametes of 2 species won’t form a zygote due to incompatibility

Postzygotic

Barriers

→ barriers that prevent the offspring from living a full and healthy life after fertilization has already occurred

-

Reduced hybrid viability

 offspring may not make it full term in pregnancy or if the baby is born, it will be very frail

-

Reduced hybrid fertility

 offspring is usually infertile (ex.

mule)

-

Hybrid breakdown

 first generation is viable and fertile, but future generations are feeble/infertile

Slide56

Other species concepts

(Besides the Biological Species Concept)

Although the biological species concept emphasizes the

separateness of species due to reproductive barriers, many alternative species concepts emphasize the unity within a species.The morphological species concept, the oldest and still most practical, defines a species by body shape and other structural features.The ecological species concept defines a species in terms of its

ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment. The phylogenetic species concept defines a species as the smallest group of individuals that shares a common ancestor

and forms one branch on the tree of life.

Slide57

Allopatric

→ geographic barriers separate and lead to the origin of a new species

Sympatric → new species arise from geographically overlapping populations; no geographical barrier (polyploidy!  see next slide!)

It all depends on if the two species, when they come back together, can interbreed or not. If they CAN – speciation has NOT occurred. If they CANNOT – speciation has occurred and there is now a new species.

Allopatric

vs. Sympatric Speciation

Slide58

Polyploid

Speciation in Plants

These occur in SYMPATRIC speciation.

Autopolyploidy

= individual that has two chromosome sets from the SAME specie; mistake in meiosis; has double the number of chromosomes (4N instead of 2N)

Allopolyploidy

= when

TWO DIFFERENT SPECIES

mate to produce

polyploid

offspring; more common than

autopolyploidy

For

example

, one species has 2n = 4 and the other 2n = 6 and the offspring has 2n = 10.

Although the hybrids are usually

sterile

, they may be quite vigorous and

propagate

asexually.

Slide59

Punctuated

Equilibrium

Punctuated equilibrium

is the idea that species evolved in “spurts” (each “spurt” could be thousands of years). This theory accounts for the variation in the tempo (rate) of speciation.

Slide60

Chapter 26 – Phylogeny and the Tree of Life

Slide61

Phylogeny and Systematics

Phylogeny

 the evolutionary history of a species or group of speciesSystematics

→ a study of biological diversity in an evolutionary contextTaxonomy

 how organisms are named and classified

THE MORE CLOSELY RELATED TWO ORGANISMS ARE, THE MORE RECENTLY THEY SHARED A COMMON ANCESTOR.

Slide62

Taxonomy

RECALL



Linneaus came up with binomial nomenclature (two-name (genus and specie) naming system based on common anatomy and morphology). A hierarchical classification groups species into increasingly inclusive taxonomic categories.

The groups start with kingdom and get more specific until species; today there are subphyla, subspecies, subfamilies, etc. The taxonomic unit at any level is called the taxon.

Slide63

Phylogenic Trees

The evolutionary history of a group of organisms can be represented in a diagram called a

phylogenetic

tree.The branching of the tree may match the hierarchical classification of groups nested within more inclusive groups.Evolutionary relationships are often represented as a series of dichotomies, or two-way branch points.Each branch point represents the divergence of two evolutionary lineages

from a common ancestor.

Slide64

RECALL



Homologous and Analogous Structures

Homologous Structures – phenotypic and genetic similarities due to a common ancestor; Ex. Forelimbs of humans, cats, whales and bats

Analogous Structures

– similarities due to the same ecological role, but different evolutionary branches, so independent (CONVERGENT) evolution of similar structures; Ex. Bat wing, bird wing

Determining whether traits are homologies or analogies is imperative when constructing a phylogenic tree.

Molecular systematics

uses DNA and other molecular data to determine evolutionary

relationships.

Slide65

Cladograms

A

cladogram

is a phylogenic tree with a series of splits and can trace back to a common ancestor of two species. They are based on homologies and physiological commonalities.

- In an approach to systematics called cladistics, common descent is the primary criterion used to classify organisms.- Biologists

place species into groups called clades, each of which includes an ancestral species and all of its descendants. - A clade is monophyletic, consisting of an ancestral species and all its

descendants

.

- When

biologists

lack information

about some members of a clade, the result may be a

paraphyletic

grouping that

consists of some, but not all, of the

descendants

.

- The

result may also be several

polyphyletic

groupings, which includes distantly related species but does not include their most recent common

ancestor.

Slide66

Shared DERIVED vs. Shared ANCESTRAL characters

Due to descent with modification, organisms share some, but not all, characteristics with their ancestors.

Systematists

must sort through homologous features, or characters, to separate shared derived characters from shared ancestral characters.A character is any feature that a particular taxon possesses.A shared derived character is an evolutionary novelty

unique to a particular clade.A shared ancestral character originated in an ancestor of the clade.

Important Point!

Slide67

Principle of Parsimony

As available data about DNA sequences increase, it becomes more difficult to draw the phylogenetic tree that best describes evolutionary history.

According to the principle of

parsimony, scientists should look for the simplest explanation that is consistent with the facts. (meaning the fewest evolutionary events or changes in DNA)Phylogenetic hypotheses (cladograms)

are stronger with more than one form of evidence (ex. fossils AND molecular)If the forms of evidence result in a different conclusion, then the molecular evidence

is favored.

Slide68

Molecular Clocks

Molecular clocks

serve as yardsticks for measuring the absolute time of evolutionary change.Molecular clocks are based on the observation that some genes and other regions of the genome evolve at constant rates.Scientists calibrate the molecular clock of a gene by graphing the number of genetic differences (nucleotide, codon, or amino acid differences) against the dates of evolutionary branch points that are known from the fossil record.The average rate of genetic change inferred from such a graph can be used to estimate the

absolute date of evolutionary events that have no fossil record.

Slide69

Fossil Record

The fossil record is the order (depth wise) in which fossils appear.

It tells us the ORDER of existence, but not exact dates

. This is considered

relative dating

.

Slide70

The next few slides are not in your notes, but they are important to this unit…so print them out and add them to your notes.

Slide71

Radiometric Dating

Radiometric dating is called “absolute dating.” It uses radioactive isotopes with known half lives and can calculate the age of a fossil in

years

.

Slide72

Racemization

Racemization is a process of determining how old an organism is after it dies. When living, organisms only produce amino acids in the L form. Racemization turns the AA into the D form at a constant rate. By comparing the ratio of the two forms, scientists can determine how old something is. This procedure is not very reliable though because the process of

racemization

is temperature sensitive.

Slide73

Exaptations

A multi-stage example of an exaptation involves human hands, which evolved to facilitate tool use and which are an exaptation of primate hands that were used for grasping tree branches. Those primate hands, in turn, were an exaptation of front legs that were used for locomotion on the ground, and those legs were an exaptation of the fins of fish, which were used for locomotion in the water.

A behavioral example is subdominant wolves licking the mouths of alpha wolves as a sign of submissiveness. (Similarly, dogs, which are domesticated wolves, lick the faces of their human owners.) This trait can be explained as an exaptation of wolf pups licking the faces of adults to encourage them to regurgitate food.

An

exaptation

is a structure that evolved and functioned in one environment, but that has an additional function in another environment. Example: Birds hollow bones – now they make the bird lighter so that it can fly, but they evolved BEFORE birds flew, so they must have had an additional function in a previous environment

Slide74

Allometric Growth

Allometric growth

is the rate of growth that gives its body its specific shape and proportions. If it is changed even slightly, it can have a drastic effect on the adult form.

Slide75

Mass Extinctions

Permian Mass Extinction

→ 250

mya

;

pangea

formed; massive volcanic activity and sharp decrease in temperature; there was little ocean water mixing so the oceans had very little oxygen in the water = 90% of ocean life became extinct

Cretaceous Mass Extinction

→ 65

mya

; Death of the dinosaurs; impact hypothesis; darkened the earth for years (dust) so no photosynthesis = food chain collapsed