Evolutionary Processes and Patterns

C

^HAPTER

8

P ROCESSES OF E VOLUTION ,

E VOLUTIONARY P ATTERNS ,

R ATES AND T RENDS

L

^EARNING

O

^UTCOMES

1. Early belief

2. Confounding discoveries

3. Darwin’s theory natural selection

4. Evolution, variation in population

5. Mutation

6. Genetic drift

7. Gene flow

¢ You will……..

— understand how heritable traits that define each species evolve

— learn about the physical evidence of past changes

W

HY LEARNING THIS CHAPTER IS IMPORTANT

?

PART 1:

OVERVIEW OF EVOLUTION

commons.wikimedia.org/wiki/Image:Charles_Darwin_1881.jpg commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG

¢ https://www.youtube.com/watch?v=hOfRN0KihO U

EVOLUTION

¢ All living things share a common ancestor.

¢ Evolution is the change over time in one or more inherited traits found in populations of

organisms.

Life forms reproduce to make offspring.

The offspring differs from the parent in minor random ways.

If the differences are helpful, the offspring is more likely to survive and reproduce.

This means that more offspring in the next generation will have the helpful difference.

These differences accumulate resulting in changes within the population.

Over time, populations branch off to become new species as they become geographically separated and genetically isolated.

This process is responsible for the many diverse life forms in the world today.

EVOLUTION

Rodin’s

“The Thinker”

• Confusion sometimes arises as to

whether Evolution is a theory or a fact.

•Actually it is both!

• The theory of Evolution deals with how

evolution happens. Our understanding of this process is always changing.

• Evolution is also a fact as there is a huge amount of indisputable evidence for its occurrence.

EVOLUTION AS THEORY AND FACT

¢ Populations : one group of individuals of the same species in a specified area.

¢ Populations show variation in shared traits.

— Eg: Variations include color or amount of hair.

¢ The Gene Pool : All genes of a population comprise the gene pool, a pool of genetic resources.

¢ Alleles: Slightly different forms of the same gene. For example, the one of the genes for hair colour comprises brown/blonde alleles.

¢ Genotype: An individual’s collection of alleles.

¢ Phenotype: Variation in appearance- alleles are the primary source of variation in appearance.

T

^ERMS

¢ Polymorphisms : occur when genes have 3 or more alleles that persist in a population with a frequency of at least 1%.

— Eg: The ABO alleles for human blood type.

¢ Dimorphisms represent 2 distinct traits, like male- female sex.

¢ Mutations are the source of new alleles.

¢ Offspring inherit the genotype, not the phenotype.

T

^ERMS

PART 2:

D ISCOVERIES OF EVOLUTION

commons.wikimedia.org/wiki/Image:Charles_Darwin_1881.jpg commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG

en.wikipedia.org/wiki/The_Creation_of_Adam

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^ISCOVERY

(1) F

IXED SPECIES

¢ From Classical times until long after the Renaissance, species were considered to be special creations, fixed for all time..

¢ Species were static and fixed, their adaptation and complexity designed by God, and varieties showed minor differences caused by local conditions.

¢ Around 1800, scientists began to wonder whether species could change or transmute.

¢ Jean Baptiste de Lamarck thought that if an animal acquired a characteristic during its lifetime, it could pass it onto its offspring.

¢ Hence giraffes got their long necks through generations of straining to reach high branches.

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^ISCOVERY

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RANSMUTATION

http://en.wikipedia.org/wiki/

ImageWilliam_Smith.g.jpg

http://en.wikipedia.org/wiki/Image:

Geological_map_of_Great_Britain.jpg

http://en.wikipedia.org/wiki/Image:Smith_fossils2.jpg

William Smith, his geology map & some of his fossil specimens At about the same time, geologists like William Smith were

mapping the rocks and fossils of Britain. He and others showed that different species existed in the past compared with today.

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^ISCOVERY

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^{OSSILS AND}

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^TRATA

¢ From 1831-1836, a young naturalist called Charles Darwin toured the world.

¢ He was dazzled by the amazing diversity of life and started to wonder how it might have originated.

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^ISCOVERY

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^ARWIN

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^S

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^OYAGE

en.wikipedia.org/wiki/Image:Darwin%27s_finches.jpeg

¢ In Origin of Species, published in 1859, Darwin

proposed how one species might give rise to another.

¢ Where food was limited, competition meant that only the fittest would survive.

¢ This would lead to the natural selection of the best adapted individuals and eventually the evolution of a new species.

Darwin in 1860

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^ISCOVERY

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URVIVAL OF THE

F

^ITTEST

Mendel and his peas • From 1856-63, a monk called

Gregor Mendel cultivated 29,000 pea plants to investigate how evolution worked i.e., how characteristics were passed down the generations.

• He figured out the basic principles of genetics. He showed that offspring

received characteristics from both parents, but only the dominant characteristic trait was expressed.

• Mendel’s work only came to light in 1900, long after his death.

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^ISCOVERY

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^ENETICS

• In the early 20^th century, scientist started to make sense of how evolution worked.

• Building on Mendel’s genetics, studies

showed how characteristics in a population could be selected by environmental

pressures.

• This Modern Synthesis, as Julian Huxley called it, brought Darwin’s Natural

Selection back to the centre of evolutionary theory.

en.wikipedia.org/wiki/Image:Hux-Oxon-72.jpg

Julian Huxley and the

Modern Synthesis

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^ISCOVERY

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^AKING

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^ENSE

www.templeton-cambridge.org/fellows/vedantam/publications/2006.02.05/eden_and_evolution/

• Despite the achieval of scientific consensus on

evolution, some Christian groups continued to

oppose the concept.

• In 1925, the teaching of evolution was outlawed in Tennessee, USA.

Outside the Scopes Trial

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^ISCOVERY

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^PPOSITION

PART 3:

E VIDENCES OF EVOLUTION

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en.wikipedia.org/wiki/Image:ATP-xtal-3D-sticks.png

DNA for Information

Transfer

ATP for Energy Transfer

• The basic similarity of all living things suggests that they evolved from a single common ancestor.

• As we have already seen, all living things pass on information from generation to generation using the DNA molecule.

• All living things also use a molecule called ATP to carry

energy around the organism.

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^VIDENCE

(1): B

IOCHEMISTRY

• If evolution is true then we might also expect that closely related organisms will be more similar to one another than more distantly related organisms.

• Comparison of the human genetic code with that of other organisms show that chimpanzees are nearly genetically identical (differ by less than 1.2%) whereas the mouse differs by ≈15%.

HUMAN CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA CHIMPANZEE CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCATGACTGTTGAACGA GORILLA CCAAGGTCACAACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA

Genetic code of chimps and gorillas is almost identical to humans

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^VIDENCE

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^IMILAR

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^ENES

en.wikipedia.org/wiki/Image:Primatenskelett-drawing.jpg

Human and Gorilla

• Similar comparisons can be made based on anatomical evidence.

• The skeleton of humans and

gorillas are very similar suggesting they shared a recent common

ancestor, but very different from the more distantly related

woodlouse…

•yet all have a common shared characteristic: bilateral symmetry

Woodlouse

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^VIDENCE

(3): C

^OMPARATIVE

A

^NATOMY

en.wikipedia.org/wiki/Image:Evolution_pl.png

The pentadactyl limb is ancestral to all

vertebrates…

but modified for different uses

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^VIDENCE

(4): H

^OMOLOGY

The coccyx is a vestigial tail

• As evolution progresses, some structures get side-

lined as they are not longer of use. These are known as

vestigial structures.

• The coccyx is a much reduced version of an ancestral tail which was formerly adapted to aid

balance and climbing.

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^VIDENCE

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^ESTIGIAL

S

^TRUCTURES

dinosaurs humans bacteria

origins^{© NASA} complex cells

en.wikipedia.org/wiki/Image:Eopraptor_sketch5.png

© World Health Org.

The fossil record shows a sequence from simple bacteria to more complicated organisms through time and provides the most compelling evidence for evolution.

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^VIDENCE

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^OSSIL

R

^ECORD

en.wikipedia.org/wiki/Image:Archaeopteryx_lithographica_paris.JPG

Archaeopteryx is the earliest and most primitive bird known

• Many fossils show a clear transition from one

species, or group, to another.

• Archaeopteryx was found in Germany in 1861. It

share many characteristics with both dinosaurs and

birds.

• It provides good evidence that birds arose from

dinosaur ancestors.

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^VIDENCE

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RANSITIONAL

F

^OSSIL

evolution.berkeley.edu/evosite/lines/IVCexperiments.shtml en.wikipedia.org/wiki/Image:Kangaroo_and_joey03.jpg

Marsupials

• Geographic spread of organisms also tells of their past evolution.

• Marsupials occur in 2 populations today in the Americas and Australia.

• This shows the group evolved before the

continents drifted apart

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^VIDENCE

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^EOGRAPHY

http://en.wikipedia.org/wiki/Image:Antibiotic_resistance.svg

en.wikipedia.org/wiki/Image:Staphylococcus_aureus%2C_50%2C000x%2C_USDA%2C_ARS%2C_EMU.jpg

• We are all familiar with the way that certain

bacteria can become resistant to antibiotics

• This is an example of natural selection in action. The antibiotic acts as an

environmental pressure.

• It weeds out those bacteria with low resistance and only those with high resistance survive to reproduce.

Staphylococcus

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^VIDENCE

(9): A

NTIBIOTIC RESISTANCE

PART 4:

M ECHANISMS AND PROCESSES OF EVOLUTION

commons.wikimedia.org/wiki/Image:Charles_Darwin_1881.jpg commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG

• The genetic make-up of an organism is known as its genotype.

• An organism’s genotype and the environment in which it lives determines its total characteristic

traits

i.e. its phenotype.

Phenotype Genotype

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^ECHANISM

(1): A

LL IN THE GENES

Watson and Crick and their model of DNA

DNA replication

• The double-helix structure of DNA was discovered in 1953.

• This showed how genetic information is transferred from one cell to another almost without

error.

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^ECHANISM

(2): DNA

upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png humansystemstherapeutics.com/bb.htm

Types of mutation • However, occasional mutations or copying errors can and do occur when DNA is replicated.

• Mutations may be caused by radiation, viruses, or carcinogens.

• Mutations are rare and often have damaging effects. Consequently

organisms have special enzymes whose job it is to repair faulty DNA.

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^ECHANISM

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^UTATION

¢ Many mutations give rise to structural, functional, or

behavioral alterations that reduce an individual’s chances of surviving and reproducing.

¢ Mutations can be lethal, neutral, or beneficial.

— Lethal mutations : usually arise from drastic changes in phenotype.

— Neutral mutations : alter the base sequence of DNA but have no effect on survival or reproduction.

— Beneficial mutation: enhances survival or reproduction.

¢In these cases, natural selection will favor the transmission to the next generation.

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^UTATION

¢ Lethal mutation (Lethal congenital contractural syndrome 3

Beneficial mutation

¢ Neutral mutation

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^UTATION

• Mutant alleles spread through a population by sexual reproduction.

• If an allele exerts a harmful

effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed

from the population.

• In contrast, mutants with

favorable effects are preferentially passed on.

Selection of dark gene

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^ECHANISM

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^ATURAL

S

^ELECTION

¢ Natural selection refers to differential survival and reproduction among individuals.

— Some traits are more adaptive in prevailing environments.

— Natural selection influences all levels of biological organization.

¢ Selection can be directional, stabilizing, or disruptive.

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^ATURAL

S

^ELECTION

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^ATURAL

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^ELECTION

¢ A shift in the average value of a trait to one direction only over time.

¢ Occurs when allele frequencies shift in a consistent direction, and forms at one end of the range of

phenotypic variations become more common than the intermediate forms.

¢ Eg: Resistance to Antibiotics

Organisms slowly getting taller.

A. D

^IRECTIONAL

S

^ELECTION

¢ Genetic diversity decreased as the population stabilizes on a particular trait value.

¢ It does not result in evolutionary change.

¢ Eg:

— Birth weights in human babies.

¢Underweight: easy to get infection

¢Overweight: difficult to deliver

B. S

^TABILIZING

S

^ELECTION

¢ Selection for extreme trait values and results in 2 different values with selection against the average value.

¢ Eg:

— Rabbit: black (BB), grey (Bb) and white (bb) in area with black & white rocks. Black & white rabbit can hide in the black & white rocks, respectively, but the grey rabbit cannot hide from predators.

C. D

^ISRUPTIVE

S

^ELECTION

¢ Special case of natural selection.

¢ Selection on any trait that increasing mating success by increasing the attractiveness of an organism to

potential mates.

— Traits are particularly prominent in male: eg bright color that attract predators à decreased survival rate.

— But, this is balanced by higher reproductive success in males that show these sexual traits.

Peahen & peacock

Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the Tufted Coquette Lophornis ornatus, female on left, ornamented male on right.

D. S

^EXUAL

S

^ELECTION

¢ Eg: Male Northern Elephant Seals fight fiercely each year. Unsuccessful males might not mate at all, while successful males have harems of 30 to 100 females.

D. S

^EXUAL

S

^ELECTION

• The dog is another example of how selection can change the frequency of alleles in a population.

• Dogs have been artificially selected for certain characteristics for many years, and different breeds have different alleles.

• All breeds of dog belong to the

same species, Canis lupus (the wolf) so this is an example of

Microevolution as no new species has resulted.

Dogs are wolves

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^ECHANISM

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ICROEVOLUTION

www.ingala.gov.ec/galapagosislands/images/stories/ingala_images/galapagos_take_a_tour/small_pics/galapagos_map_2.jpg

Galapagos finches

• However, if two populations of a species become isolated from

one another for tens of thousands of years, genetic difference may become marked.

• If the two populations can no- longer interbreed, new species are born. This is called

macroevolution.

•Macroevolution refers to evolution above the species level.

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^ECHANISM

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ACROEVOLUTION

¢ The basic evolutionary mechanisms—mutation,

migration, genetic drift, and natural selection—can produce major evolutionary change if given enough time.

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ACROEVOLUTION

•When interbreeding between populations (exp.

Geographically isolated) is difficult, it is suggesting that speciation may be occurring.

•Exp: Genetic changes resulted in two separate fruit fly lineages. But why and how did it happen?

•The two portions of the population, mainland and island, are now too far apart for gene flow to unite them.

•After a long period of time, these populations have evolved different courtship behaviors.

•The lineage has split now that genes cannot flow between the populations as different behaviour will restrict mating

(reproductive isolation).

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^ECHANISM

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^PECIATION

S

^PECIATION

_S

^OURCE

S

^PECIATION

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^YPES

¢ Allopatric

— A population splits into two geographically isolated populations.

— Eg: Spotted owl subspecies living in different geographic locations show some genetic and morphological differences.

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^PECIATION

_T

^YPES

¢ Peripatric

— New species are formed in isolated, smaller populations that are prevented from exchanging genes with the main

population.

— It is related to the concept of a founder effect, since small populations often undergo bottlenecks.

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^PECIATION

_T

^YPES

¢ Parapatric

— Continuous variation within a single, connected habitat.

— There is no specific extrinsic barrier to gene flow.

The population is continuous, but does not mate randomly.

— Two types of plants have evolved different flowering times. Although continuously distributed, different flowering times have begun to reduce gene flow

between metal-tolerant plants and metal-intolerant plants.

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^PECIATION

_T

^YPES

Grass species Anthoxanthum odoratum

¢ Sympatric

— The formation of two or more descendant species from a single ancestral species in the same

geographic location.

— Exp: Gene flow has been reduced between maggot

flies that feed on different food varieties, even though they both live in the same geographic area.

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^PECIATION

_T

^YPES

¢ Genetic equilibrium can only occur when the following 5 conditions are met:

1. mutations do not occur;

2. the population is infinitely large;

3. the population stays isolated from all others of the same species;

4. mating is random;

5. all members of the population survive and produce the same number of offspring.

¢ In nature, all 5 conditions are never met; this results in small-scale changes in the population’s allele frequency.

This is called microevolution.

STABILITY AND CHANGE IN ALLELE FREQUENCIES

¢ The Hardy-Weinberg Formula can be used to track whether a population is in genetic equilibrium or not.

— The mathematical formula tracks allele frequency for a specific trait.

— Researchers can use the formula to estimate the frequency of carriers of alleles that cause genetic traits and disorders.

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^{HEN IS A}

P

^OPULATION

N

^OT

E

^VOLVING

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p 2 + 2pq + q 2 = 1

p + q = 1

p= frequency of allele A q= frequency of allele a

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^ANDY

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^EINBERG

F

^ORMULA

¢ 1. Natural selection (discussed earlier)

¢ 2. Genetic drift

— Is the change in allele frequencies from one generation to the next due to chance

occurrences alone.

— It is more significant in small populations.

A

^LTERING

E

^XISTING

G

^ENETIC

V

^ARIATION

Rate of Loss = ¹/_2N

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^LTERING

E

^XISTING

G

^ENETIC

V

^ARIATION

¢ Genetic drift (eg: disaster such as fire, hurricane, hunting etc) can reduce the size of a population drastically.

¢ Genetic drift will cause big losses of genetic variation for small populations, thus the genetic of the left over

population maybe different than the original population

— Causing population bottleneck!!!

¢ Population bottlenecks occur when a population’s size is reduced for at least one generation.

¢ Reduced genetic variation means that:

— The population may not be able to adapt to new

selection pressures, such as climatic change because the genetic variation may have already drifted out of the population.

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^LTERING

E

^XISTING

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^ENETIC

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^ARIATION

An example of a bottleneck:

¢ Northern elephant seals have reduced genetic variation.

¢ Hunting by human 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.

A

^LTERING

E

^XISTING

G

^ENETIC

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^ARIATION

¢ 3. Gene flow

— Known as ‘gene migration’.

— The transfer of alleles of genes from one population to another.

¢Either by emigration (move out) or immigration (move into) a population.

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^LTERING

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^XISTING

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^ENETIC

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^ARIATION

C

^OEVOLUTION

¢ Coevolution is a change in the genetic composition of one species (or group) in response to a genetic change in another (mutual evolutionary).

¢ It is likely to happen when different species have close ecological interactions, eg:

— Predator/prey and parasite/host

— Competitive species

— Mutualistic species

¢ Coevolution cause:

— Each species adapts to changes in the other.

— Over time the two may become interdependent.