Download Chapter 15 notes I. Darwin`s Voyage and Discovery A. 1809 Charles

Chapter 15 notes
I. Darwin’s Voyage and Discovery
A. 1809 Charles Darwin – Father of Evolution. Naturalist from England. Sailed on the
surveying ship HMS Beagle and traveled to various lands.
B. During his travels, Darwin made numerous observations and collected evidence that led
him to propose a revolutionary hypothesis about the way life changes over time.
C. Darwin’s Observations
1. Patterns of Diversity – organisms seemed well suited to their environment!
a. There were SO many different types of similar organisms
1. 68 different types of beetles in the Brazilian rainforest
2. What leads to this variety?
3.Why were certain types or organisms only found in certain areas?
4.How were they so well suited for their environment?
b. Remember from our ecology unit, only one species can occupy a particular
niche at a particular time.
2. Living Organisms and Fossils – Darwin collected the preserved remains of ancient
organisms from many places (fossils).
a. Why have so many species disappeared and how were they related to living
things?
3. Species Vary Globally
a. Different, yet ecologically similar animals species inhabited separate, but
ecologically similar, habitats around the globe
1. Rheas (bird)—flightless, lived in South America
2. Ostrich (bird)—flightless, lived in Africa
b. Some species were only found in certain parts of the world
1. Rabbits were only found in Europe (at the time) and not found in
South America or Australia
2. Kangaroos were only found in Australia.
4. Species Vary Locally
a. The Galapagos Islands
1. One of the most influential places - off the coast of S. America.
2. Close together
3. very different climates with very different organisms
1. from hot, dry  nearly barren; lots of plants  few plants
2. Finches – 16 different types of birds – differed in color and
beak shape (based on what they ate)
3. Tortoises – varied from one island to another.
Darwin observed that the characteristics of many animals and plants varied noticeably among the
different islands of the Galapagos.
II. Ideas that Shaped Darwin’s Thinking
A. An Ancient changing Earth.
1. Originally the earth and its life forms were thought to be a few thousand years old.
2. Darwin questioned this – how could all of this change have happened in such a short
time?
B. Hutton and Geological Time (1795)
1. Certain kinds of rocks are formed from molten lava.
2. Some rocks form very slowly.
3. Forces beneath Earth’s surface can create mountain ranges.
4. Environmental forces (wind, rain, heat, cold) can wear down mountain ranges
(Erosion)
5. CONCLUSION—the Earth must be older than a few thousand years.
C. Lyell’s Principles of Ecology
1. Scientists must explain past events in terms of processes that they can observe.
a. Uniformitarianism--Geological processes that we see today must be the same ones
that shaped the Earth millions of years ago.
1. Ex. Ancient volcanoes release lava just like they do today
2. Earth must be older than originally thought due to all of the mountains and
river formations – they didn’t just appear.
D. Lamarck’s Evolutionary Hypothesis.
1. Living things have changed over time by selective use or disuse of organs, organisms
acquired or lost certain traits. (Example: Blacksmith’s arm or a giraffe’s neck)
2. Tendency towards perfection: organisms change and get new features to help them be
‘better’
a. Bird can acquire longer legs if it needed to wade in deeper water
3. Use and disuse: organisms can alter their body shape by using their bodies in different
ways or lose parts by not using them
a. If bird stopped using its wings for flight then the wings would get smaller.
4. Inheritance of acquired traits: if an organism acquired a new trait – it would pass it on
to it’s offspring
a. If The Rock (Dwayne Johnson) acquired large muscles then these muscles could be
passed on to offspring.
**We now know Lamarck’s ideas were incorrect. Organisms don’t have an inborn drive to…
1. Be ‘better’—Evolution does not mean that species become better or progresses in a predetermined direction.
2. Body parts don’t change in one lifetime
3. Cannot pass along traits we acquire (such as muscles) to our offspring.
E. Population growth
1. Malthus (1798) noticed that humans were being born faster than they were dying,
causing overcrowding.
2. Three things will prevent overpopulation
a. War: over space/resources
b. Famine: lack of resources
c. Disease: sanitary/close proximity
3. Darwin reasoned that Malthus’s reasoning could apply to organisms other than
humans
a. This gave Darwin the mechanism for evolution
1. Most organisms die before reaching maturity (can’t reproduce)
2. Only a few survive to reproduce
3. Darwin wondered, ‘Why do some organisms live and some die’?
F. Artificial selection
1. Artificial Selection: Selective breeding of plants and animals to promote the
occurrence of desirable traits in offspring
2. Darwin studied change produced by plant and animal breeders.
a. Some variation can be passed from parent to offspring.
1. Example: Farmers can breed only tree that produce largest fruit.
2. Example: Farmers breed largest cows and bulls to produce large offspring.
III. Darwin Presents His Case
A. History
1. Darwin wrote a full draft of his ideas on evolution but put it away for 20 years.
a. Didn’t want to be ridiculed for radical ideas
2. Alfred Russell Wallace wrote an essay with ideas similar to Darwin’s, however Darwin had more
evidence.
3. Darwin didn’t want to be ‘scooped’ and published his book
On the Origin of Species’ .
B. Evolution by Natural Selection.
1. The struggle for existence
a. Darwin reasoned that processes similar to artificial selection worked in nature
2. Variation and Adaptation
a. Darwin knew all organisms are different (variation within a population)
b. Darwin hypothesized that some organisms are therefore better suited to environment than
others
c. Adaptation: any inherited characteristic that increases an organism’s chance of survival.
3. Survival of the fittest
a. Fitness – ability to survive and reproduce in its environment.
1. High fitness—organisms that can survive and reproduce
2. Survival of the fittest—The difference in rate of survival and reproduction
4. Natural Selection – process by which individuals that are better suited to their environment
survive and reproduce most successfully (survival of the fittest)
a. Based on the following
1. Variation exists within the population
2. Natural HERITABLE var
+iation exists
3. Fittest individuals tend to leave the most offspring
4. Different reproductive success within a population
5. Population tends to produce more individuals than the environment can support (survival
of the fittest)
b. Natural selection is NOT based on
1. Making organisms ‘better’.
a. Adaptations don’t have to be perfect, just good enough to enable organism to pass its
genes down to next generation.
2. Does not occur in a fixed direction.
a. No perfect way of doing anything—if environment changes then some traits that were
once adaptive may no longer be useful and different traits may become adaptive
5. Common Descent
a. Descent with modification – over long time, natural selection produces organisms that have
different structures, establish different niches, or occupy different habitats. (that’s why they
look different from their ancestors)
b. Darwin developed the theory that all organisms are related.
1. Ancestral tree.
IV Evidence for Evolution
A. Darwin argued that living things have been evolving on earth for millions of years
B. Biogeography
1. Biogeography—The study of where organisms live now and where they and their ancestors lived
in the past.
a. Closely related but different—Biogeography of Galapagos species suggested populations had
evolved from mainland species.
b. Distantly related but similar—Similar ground-dwelling birds inhabit Europe, Australia, and
Africa.
1. This was evidence that similar natural selection pressures had caused distantly related
species to develop similar adaptations.
C. The Age of Earth and Fossils
1. The age of Earth
a. Geologist use radioactivity to determine age of Earth
b. Earth is 4.5 billion years old.
2. Recent Fossil Finds
a. Fossils – fossils lower in rocks and mountains are older than those in higher areas.
1. Organisms changed a LOT over time.
2. Gaps remain in the fossil record.
3. Recent discovery—whales evolved from ancient land mammals.
a. Evidence—Whales retained a pelvic bone and in some cases upper and lower limb
bones (no longer play a role in locomotion).
D. Comparing Anatomy and Embryology
1. Homologous body structures – structures that have different mature forms but develop from the
same embryonic tissue. Provide evidence that all four-limbed vertebrates have descended with
modifications from common ancestors—Example of divergent evolution
2. Vestigial Organs – organs of many animals are so reduced in size that they are just vestiges, or
traces of homologous organs in other species. It may not affect an organisms ability to survive
and reproduce, so natural selection did not eliminate the organ.
Tail bone, appendix, nictitating eyelid, wisdom teeth, goosebumps
3. Embryology – early stages of embryos of many animals with backbones are very similar. They
look really similar. (Hox genes control embryological growth).
E. Genetics and Molecular Biology
1. Genetic code and homologous structures provide evident of common ancestors
a. Remember, all organisms have the same genetic code
1. Three nitrogenous bases = one codon
2. One codon = one amino acid.
3. Same 20 amino acids occur in all organisms.
2. Homologous molecules
a. Homologous proteins are found in wide variety of organisms.
1. Cytocrhome C—functions in cellular respiration and if found in almost all living
organisms (bakers yeast  humans)
b. Homologous genes
1. Hox genes—determine head to tail axis of vertebrates (organisms with back bones) as well
as direct growth of front and hind limbs
F. Testing Natural Selection
1. A testable hypothesis
a. Hard to see natural selection as it can take millions of years.
b. Not impossible to test for natural selection!
1, Peter and Rosemary Grant recorded variation of heritable traits among Galapagos finches in
just 35 years!
2. Natural Selection
a. Grants showed—
1. Individual finches with different-size beaks have a better/worse chance of surviving both
seasonal droughts and longer dry spells.
2. When food is scarce during dry spells, finch with largest beak more likely to survive.
G. Evaluating Evolutionary theory
1. Not a question of whether evolution occurs, but HOW it occurs.
DARWINS THEORY SUMMARY
1.
2.
3.
4.
5.
Individual organisms differ, some variation is heritable
organisms produce more organisms than survive
Organisms compete for limited resources (struggle for survival)
Most fit organisms survive
species alive today are descended with modification
V. Adaptation
A. Adaptation are traits shaped by natural selection—increases an organisms reproductive success
B. Fitness—measure of the relative contribution an individual trait makes to the next generation
C. Camouflage—morphological adaptation that allows an organism to blend into their environment.
D. Mimicry—Morphological adaptation where one species evolves to mimic another species
Genes and Variation
I. Genetics Joins Evolutionary Theory
A. Modern evolution allowed us to understand what Darwin couldn’t, how evolution works.
B. Genotype and Phenotype in Evolution
1. Genotype: Genetic makeup of an organism (TT, Tt, tt)
2. Phenotype: Physical, physiological, and behavioral expression of an organism (Tall, short)
3. Natural Selection does not act directly on genes. Acts on the ENTIRE organism as the entire
organism survives, not a single gene.
C. Populations and gene pools
1. Population: A group of individuals of the same species that mate and produce offspring.
a. Populations share a common gene pool
1. Gene pool: All the genes, including all different alleles for each gene in a
population.
a. Researchers study allele frequencies.
1. Allele Frequencies: Number of times an allele occurs in a
gene pool compared to the total number of alleles in that pool
for the same gene.
** Practice Problem
Example: B = Black
You have:
b = Brown
8 Homozygous Black (BB)
24 Heterozygous Black (Bb)
18 Homozygous Brown (bb)
How many total alleles?
# of B
_______
_______
_______
_______
# of b
_______
_______
_______
_______
So, the allele frequency of “B” in the gene pool is _____________________________________
Therefore, the frequency of “b” must be _______________________________________
b. Evolution in genetic terms, involves a change in the frequency of
alleles in a population over time.
II. Sources of Genetic Variation.
A. Mutations: Change in genetic material of cell
1. Change in phenotype may or may not affect fitness
B. Genetic Recombination in Sexual Reproduction
1. Crossing over during interphase I of meiosis increases the number of new genotypes created in
each generation.
C. Lateral gene transfer: transfer of genes from one organism to another organism that is not its
offspring
1. Seen in bacteria
III. Single-Gene and Polygenic Traits
A. Single-gene trait: A trait controlled by only one gene
1. Example: Snails Shell withOUT a band is dominant over a shell WITH a dark band.
B. Polygenic trait: A trait that is controlled by two or more genes
2. Example: Height in humans, eye color, skin color
Evolution as Genetic Change in Populations
I. How Natural Selection Works
A. Fitness: A fit organism will survive and be able to reproduce passing its genes on to its offspring
B. Natural Selection on Single-Gene Traits:
1. Can lead to changes in allele frequencies, and thus, to changes in phenotype frequencies.
2. Example: Brown lizards exist in a population.
Mutation produce red and black lizards.
Red lizards are easily recognized by predators
Black lizards may warm up faster on a cold day and thus they can move faster to
feed and avoid predators
Initial Population
Generation 10
Generation 20
Generation 30
80% brown lizards
80% brown lizards
70% brown lizards
60% brown lizards
10% red lizards
0% red lizards
0% red lizards
0% red lizards
10% black lizards
20% black lizards
30% black lizards
40% black lizards
C. Natural Selection on Polygenic Traits
1. Effects of natural selection are more complex
2. Natural selection on polygenic traits can affect the relative fitness on phenotypes and thereby
produce one of three types of selection:
Natural Selection can affect the frequency of a heritable trait in a population three different ways
1. Stabilizing Selection – reduces phenotypic variation by selecting for the most
common phenotype
2. Directional Selection – shifts the overall makeup of the population by favoring
one extreme phenotype
3. Disruptive Selection – favors both extremes over the more common
Intermediate phenotype
II. Genetic Drift
A. In small populations, individuals that carry a particular allele may leave more descendants than other
individuals leave, just by chance. Over time, a series of chance occurrences can cause an allele to
become more or less common in a population.
1. Genetic Drift: Random Change in allele frequency.
2. Bottleneck effect: Change in allele frequency following a dramatic reduction in the size of a
population
a. Could be caused by a natural disaster.
b. Severe bottle neck can sharply reduce a populations genetic diversity
3. Founder Effect: Allele frequencies change as a result of the migration of a small subgroup
of a population.
a. Example #1: Several hundred species of fruit flies on different Hawaiian Islands
descended from the same mainland fruit fly population.
b. Example #2:
1. Colonists founded a British Settlement on Tristan da Cunha (small island in
Atlantic Ocean).
2. One colonist had recessive allele for retinitis pigmentosa (progressive blindness
disorder).
3. Of the 240 descendents, 4 had disorder in late 1960’s. This is 10 TIMES higher
than in original population.
III. Evolution Versus Genetic Equilibrium
A. Genetic Equilibrium: When a population is not evolving the allele frequencies in its gene pool do
not change.
B. Sexual Reproduction and Allele Frequency
1. Gene shuffling occurs during sexual reproduction.
2. Meiosis and fertilization does not change allele frequencies.
3. A population of sexual reproducing individuals could remain in genetic equilibrium
C. Hardy-Weinberg Principle
1. Hardy-Weinberg Principle: Allele frequencies of a population should remain constant unless
one or more factors cause those frequencies to change.
a. Make predictions regarding the frequencies of genotypes in the populations.
1. p2 +2pq +q2=1 where p = dominant allele
q = recessive allele
**Practice problem: Frequency of A allele is 40% (.40)
Frequency of a allele is 60% (.60)
If this population is in genetic equilibrium then what is the chance of individual in the
next generation having genotype AA, Aa, and aa
Remember p2 +2pq +q2=1
AA = _______________
Aa = ________________
aa = ________________
b. Five conditions can DISTURB Hardy-Weinberg principle
1. Nonrandom Mating—individuals must mate at random to maintain genetic
equilibrium.
2. Small Population Size—Genetic drift does not have a major effect on large
populations
3. Mutations—Mutations can introduce new alleles into a gene pool
4. Immigatraion/Emmigration
a. Individuals who join population add alleles.
b. Individuals who leave population remove alleles
5. Natural Selection—If different genotypes have different fitness, then genetic
equilibrium will be disrupted and evolution will occur.
The Process of Speciation
I. Isolating Mechanisms
A. Species: A population or group of populations whose members can interbreed and produce fertile
offspring.
B. Speciation: Formation of new species
C. Interbreeding links members of species genetically
D. Once population has split into 2 groups changes in gene pool cannot spread between groups.
1. If a population can’t interbreed they are reproductively isolated.
E. Reproductive isolation can develop 3 ways
1. Behavioral Isolation: Incapable of interbreeding due to differences in courtship rituals or
other behaviors.
a. Example: Two different species of cricket that would be indistinguishable unless you
heard their mating song: they are of a noticeably different pitch
2. Geographic Isolation: Two populations are separated by geographic barriers such as rivers,
mountains, or bodies of water.
a. Example: Polar bear and brown bear isolation due to the oceanic and glacier barriers
3. Temporal Isolation: Occurs when two or more species reproduce at different times.
a. Example: Rainbow trout spawn in the spring. Brook trout spawn in the fall. These two
species are isolated reproductively by time.
Evolution of Populations
SOURCES OF GENETIC VARIATION
1. mutations
2. gene shuffling, sexual reproduction, crossing over
Natural selection on single-gene traits can lead to changes in allele frequency and thus to evolution. Without
evolution and variation, organisms could not adapt to their environment. Environment changes a LOT!
 Climate
 Resources
 Abiotic (non-living factors)
 Biotic (living factors)
8. Name an environmental change that could cause an organism to become extinct and how it would
happen?
In a small population, individuals that carry a particular allele may leave more descendants than other
individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become
common in a population.
Five conditions are required to maintain genetic equilibrium from generation to generation: There must be:
 random mating
 the population must be very large
 there can be no movement into or out of the population
 no mutations
 no natural selection.
Speciation – populations become isolated from one another and evolve into different species
 Behavioral isolation – 2 populations are capable of interbreeding, but have differences in courtship or
other reproductive strategies.
 Geographic Isolation – 2 populations are separated by geographic barriers
 Temporal Isolation – 2 or more species reproduce at different times.
9. Why would geographically isolated populations evolve into a different species?
10. What must be true about the reproductive behavior of species that are isolated by temporal isolation?
.
17-4
11. What do the terms macroevolution and coevolution mean?
PATTERNS OF EVOLUTION
Six important topics in macroevolution are
1. EXTINCTION: 99.9% of all species ever on this earth are now extinct. Mass extinction. (most
extinctions today are due to human activity)
2. ADAPTIVE RADIATION: a single species or small group have evolved into different forms that live in
different ways. Ex. FINCHES, homologous structures
3. CONVERGENT EVOLUTION: Unrelated organism come to resemble one another. Ex. Dolphin/sharks
4. COEVOLUTION: process by which 2 species are closely connected to one another by ecological
interactions evolve together. Ex. Plants and plant eating insects
5. PUNCTUATED EQUILIBRIUM: some groups of organism have evolved rapidly after a mass
extinction.
Chapter 15: Evolution
15-1

Evolution: change over time; the process by which modern organisms have descended from
ancient organisms.
 The theory of evolution is the scientific explanation for the large amount of diversity of
life.

Theory: a well supported testable explanation of phenomena that have occurred in the
natural world.

Charles Darwin: born in England in 1809 to a wealthy physician.
o He attended medical school and studied to be in the clergy
o While at school, a botany professor approached him about a naturalist position on a
ship going on a 5 year expedition
o In 1831 Darwin set sail on the H.M.S. Beagle.
o From his travels on the Beagle, Darwin proposed a revolutionary hypothesis about the
way life changes over time.
o Along Darwin’s travels, he collected many specimens and saw much diversity among
various living species.
o He also collected fossils


Fossils: the preserved remains of ancient organisms.
Galapagos Islands: a group of islands off the coast of west South
America. Darwin noted that although they were close together, the islands had very different
climates (some were hot, dry and barren, while others were cool, lush and had abundant
vegetation).
o While visiting these islands, Darwin took an interest in the variation among tortoises’
shells on the various islands in the Galapagos.
15-2

People in Darwin’s day believed that the earth and all its inhabitants were only a few thousand
years old. They also believed that neither the planet nor its living species had changed.

They believed that major geological features (such as the Grand Canyon) were thought to
have been produced by catastrophic events that humans rarely see.

James Hutton and Charles Lyell: helped scientists recognized that
the
Earth is many millions of years old, and the processes that changed Earth in the past are the
same processes that operate in the present.

While on his journey, Darwin read Lyell’s book “Principles of Geology” that states processes
occurring now have shaped Earths geological features over long period of time. Darwin reasoned
that if earth could change of long periods of time, might life change as well?

Jean-Baptiste Lamarck: among first scientists to recognize that living things have changed
over time, that all species were descended from other species, and somehow organisms adapted
to their environments.

Lamarck proposed (in 1809) that by selective use or disuse of organs, organisms acquired or
lost certain traits. These traits could then be passed on to their offspring. Over time, this process
is what led to a change in the species. Basically he proposed the “Use it or Lose it” theory.

Thomas Malthus: In 1798 published a book stating that if the human population continued to
grow unchecked, sooner or later there would be insufficient living space and food for everyone.
Because he didn’t see this happening, Darwin questioned which factors determine which ones
survive and reproduce, and which do not?
15-3
 Origin of the Species: In 1885 Darwin received an essay from Alfred Russell Wallace
summarizing the thoughts on evolutionary change that Darwin had had for 25 years. This essay
made Darwin rush to publish a book on his thoughts. This book was the Origin of Species.
o In this book Darwin proposed evolution by natural selection.

In Darwin’s travels, he noticed that members of each species varied from one another in
important ways (example: some plants bear fruits that are bigger than others, some cows are
able to produce more milk etc.)

Artificial selection: nature provides the variation and humans select those variations that
they found useful (example: horses bred for their speed, cows bred for the largest milk
production, etc.)

Darwin was convinced that processes like artificial selection worked in nature. But he wasn’t
quite sure how.

Struggle for existence: members of each species compete regularly to obtain food, living
space and other necessities of life. Those that were able to compete and “win” would be more
likely to survive.

Fitness: the ability of an individual to survive and reproduce in its specific environment.

Adaptation: any inherited characteristic that increases an organism’s chance of survival.

Survival of the fittest: A process where individuals that are better suited to their
environment, survive and reproduce most successfully

Natural Selection: Survival of the fittest. Over time natural selection results in changes in the
inherited characteristics of a population. These changes increase a species’ fitness in its
environment.

Descent with modification: each living species has descended, with changes over long
periods of times, from other species.

Descent with modification implies that all living organisms are related to one another

Common descent: all species-living and extinct- were derived from common ancestors.

Homologous Structures: Structures that have different mature forms but develop from the
same embryonic tissues. These provide strong evidence that all four-limbed vertebrates have
descended, with modifications, from common ancestors.

Vestigial Organs: Organs that are so reduced in size that they are just vestiges, or traces, of
homologous organs in other species.

The early stages of development (embryos) of many animals with backbones are very
similar. Because of these similarities it is clear that cell development in all vertebrates is in the
same order.
Darwin’s Theories Summarized:
 Variation among species is heritable (passed from parent to offspring)
 Organisms produce more offspring than can survive, and of those that survive, many
don’t reproduce
 Because of the reproduction rates, organisms compete for limited resources individuals
best suited to their environment are able to survive, reproduce and pass on their traits;
those that cannot die or leave fewer offspring.
 All species alive today, are descended with modification from ancestral species.