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Honors Biology Chapter14 – Evolution: A History and a Process
p. 290- 321
(Although species have changed over time, all life on earth is related and descended from the first microbes.)
Concept 14.1: Darwin developed a Theory of Evolution
(Darwin’s The Origin of Species in 1859 provided a way to understand Earth’s diversity of orgs + their relshps.)
I. Ideas from Darwin’s Time
A. Evolution = all the changes that have transformed life over an immense time.
B. Pre-Darwin ideas about life
1. species are fixed – they do not change
2. earth is less than 10,000 years old and relatively unchanged
*Both ideas challenged as people learned more.
C. Some famous names in Evolutionary/Geologic history
1. Buffon – proposed Earth much older than 10,000 years
2. Lamarck – proposed life evolved as a process of adaptation
a. Adaptation = an inherited characteristic that improves an organism's ability to survive
and reproduce in a particular environment (Ex. Kangaroo hind legs for hopping)
b. Wrong idea about how adaptations evolve – read p. 293
1.) Inheritance of Acquired characteristics (See Fig. 14.2 p. 293)
2.) Faulty – acquired char. would have to modify DNA to be passed to next gen.
c. set stage for Darwin’s ideas
II. The Voyage of the HMS Beagle (1831, 22 yr old)
A. What the voyage was for – Read p. 293, and see Fig. 14.3
B. Darwin’s Observations (read p. 294)
1. observed + collected 1000’s of spec. of South Am. plants and animals from diverse envir.
2. maintained extensive journals of his observations, studies, and thoughts
3. before voyage felt concept of fixed species best described nature.
4. after returning to Eng. was convinced that species change as they adapt to their chging. envir.
5. Galapagos studies (See fig. 14.4, p. 294) – species on each island diff. from other islands &
mainland, yet quite similar in some ways
a. inferred from these observations that mainland species had changed after they
colonized the islands & adapted to their various envir.
C. Ideas from Geology (Read p. 295)
1. Lyell - proposed that gradual and observable geologic processes such as erosion could explain
the physical features of today's Earth (see Fig. 14.5, p. 295)
a. Darwin found fossils of marine orgs high in Andes mtns, + saw earthquake lift sea
floor above water
b. 2 conclusions:
1.) Earth must be very old for slow geologic processes to have formed it
2.) Those slow processes could cause enormous change
III. Darwin Publishes his Theory (read p. 296-297)
A. Was convinced that Earth was ancient and that species can change through time
-but by what mechanism?
B. See Fig. 14.7, p. 296 – summary of Darwin’s experiences
C. Malthus – theory of how human population grows – Darwin thought idea applied to all species
1. production of more individuals than the envir. can support leads to a struggle for existence
2. led to devel of Darwin’s concept of how evol. change occurs
3. wrote a paper about it in 1844, but did not publish it
D. Wallace – came to same conclusions as Darwin, but not until 1858 – both presented ideas to public at
that time, Darwin published his book the next year
IV. Darwin’s Two Main Points (Read p. 297, see Fig. 14.8)
A. Descent with Modification =
1. species of organisms living on Earth today descended from ancestral species
2. descendants of the earliest organisms spread into various habitats over millions of years
3. In these habitats, they accum. diff. modifications, or adaptations, to diverse ways of life
4. descent with modification as a way to account for the diversity of life
a. Ex. Jackrabbit and snowshoe hare
B. Natural Selection = process by which individuals with inherited characteristics well-suited to the
environment leave more offspring on average than do other individuals (See Fig. 14.9, p. 298)
1. Mechanism for Evolution
2. This process can cause a population to change over time
3. Darwin’s theory of evol. is actually his theory of natural selection as a cause of evol.
4. Result of N.S. = Adaptation
Concept 14.2: Evolution has left Much Evidence
(Evidence for evolution is in fossil record and in diversity of modern species.)
I. The Fossil Record
A. Fossil = Preserved remains or markings left by organisms that lived in the past
1. Found usually in sedimentary rock
a. Read p. 299 and see fig. 14.10 for process of how fossils form
2. Position of fossil in rock layers (strata) – shows relative age
B. Fossil Record = chronol. collection of life's remains in rock layers, recorded during passage of time
1. Oldest fossils – chem.. traces in rocks of Greenland 3.8 billion years old
2. Prokaryote (bacteria) fossils - in rocks about 3.5 bil yrs old
a. support data from molecular and cell evidence that bacteria oldest form of life
3. Eukaryotic fossils – in younger layers of rock, record evol of various groups
4. Fossils of Extinct species – help reconstruct the past
a. Ex. Whales living about 40 mil yr ago – had hind limb bones
1.) Supports hypo. that whales evol. from land-dwelling ancestors w/ 4 limbs
2.) See Fig. 14.11 and read p. 300
II. Geographic Distribution
A. Patterns in Geog. Distribution of life forms
1. Darwin observed sim. & diff. in orgs in diff parts of world –evolved from common ancestors
2. Ex. Australia – marsupials, very few placental mammals – why?
a. most widely accepted hypothesis suggests that Australia's diverse marsupial species
evolved from marsupial ancestors on an island continent that was isolated from placental
mammals
3. Ex. 2 islands w/similar envir. in diff. parts of world
a. more simil. w/ species on closes mainland than on the other island – why?
b. descended from species in that geographic region (the mainland)
c. origin of new species closely linked to changing geog. + envir. conditions
III. Similarities in Structure (among Species)
A. Provide clues to evolutionary history
1. Ex. Forelimbs of all mammals consist of the same skeletal parts (See fig. 14.13, p. 301)
a. Functions of them differ, though
b. Homologous Structures = parts with similar structure that have widely diff. functions
1.) support other evidence that evolution is a remodeling process
a.) Ex Structures functioning one way in ancestral species become
modified as they take on new functions (Darwin)
b.) may be “less than perfect” as a retrofit (read p. 302)
2.) Vestigial structures = are remnants of structures that may have had impt.
functions in ancestral species, but have no clear function in some
modern descendants
a.) usually reduced in size
b.) Ex. whales vestigial hip bones
c.) Ex. Goosebumps in humans when they are cold (See Fig. 14.14 p. 302)
IV. Similarities in Development
A. Embryos of closely related orgs often have similar stages of devel.
1. Ex. Vertebrates – See Fig. 14.15, p. 303
a. embryonic stage in which pouches appear on the sides of the throat
b. at this stage, embryos of fish, frogs, snakes, birds, + primates look relatively alike
c. evid. of common ancestry
2. Ex. limb bones in mammals – follow similar stages of development
V. Molecular Biology (read p. 303)
A. Among siblings, the DNA and protein sequences are very similar
B. Sequences of unrelated individuals of the same species show more differences
1. If two species have genes and proteins with sequences that match closely,
- conclude that the sequences have been inherited from a relatively recent common ancestor
2. The greater the number of diff.in DNA and protein sequences between species,
the less likely they share as close a common ancestry
C. DNA and protein analyses are new tools for testing hypo.about evolution
1. Ex. Fossils show that humans, chimps and gorillas are closely related
a. if humans and other primates are closely related, then they should share much of
their inherited DNA and protein sequences (sequences of distantly related species
)should have more differences
b. See Fig. 14.16, p. 304 – A.A. seq. of human hemoglobin with that of other vertebrates
1.) only 5% diff. between humans and chimps sequence in the total DNA!
VI. Summary of Section 14.2 – All life forms are related with evidence in the common genetic code.
Concept 14.3: Darwin proposed Natural Selection as the Mechanism for Evolution
(Natural Selection is our best explanation for adaptive evolution.)
I. Darwin’s Theory of Natural Selection
A. Population = a group of individuals of the same species living in the same area at the same time
1. Ex. Galapagos Finches – as pop.on each island adapt to their diff. envir., change from the orig.
pop. that colonized the island
B. Observations Lead to a Question
1. 13 species of finches unique to the Galapagos’ – most closely resemble 1 mainland species
2. How did they get diff. beaks? (their beak shapes match food sources on each island)
a. Darwin’s answer – natural selection favored adaptation of diff. shaped beak
b. See Fig. 14.17, p. 305
C. More Observations Lead to an Idea – Read p. 3306
1st set. (Malthus) - all species tend to produce excessive numbers of offspring. But in nature,
resources are limited.
a. only a small percentage of offspring will survive in each generation
b. rest are starved, eaten, frozen, diseased, unmated, or unable to reprod for other reasons
nd
2 set -Variation exists among the individuals of a population
a. Variation = differences among members of the same species
b. Much of this variation is heritable
c. Why siblings usually share more traits with one another + parents than they do with
unrelated members of the same population
3. Darwin developed Theory of Natural Selection from these 2 sets of observ.
a. See Fig. 14.19, p. 306 for Flowchart
b. Survival of the Fittest = Individuals with inherited traits that are best suited to the local
environment are more likely to survive and reproduce than less fit individuals=
leave the most offspring
c. can cause 2 isolated pop. of same species to become sep. species (finches ex.)
II. Artificial Selection = selective breeding of domesticated plants and animals to produce offspring with
genetic traits that humans value
A. Provided evidence for Darwin
1. Breeders play role of envir. by selecting orgs with desired traits to reproduce
a. Ex. Crops – disease resistance or grain prod.
b. Ex. Animals – growth rate or temperament
2. We have been modifying species for 100’s of years this way
a. Ex. dog breeds (or anything!) See fig. 14.20, p. 307
B. Compare/contrast artificial and natural selection – Read p. 307
III. Pesticides – Natural Selection in Action
A. Natural selection may be observable – esp. in orgs with short generation time
1. Ex. insects and pesticide resistance – Read p. 307-308, See Fig. 14.21 p. 308
a. 2 key points of natural selection illustrated:
1.) Natural selection is a process of "screening" traits that are available
a.) N.S. does not create the indiv. w/the trait, just selects those indiv.
already present
2.) N.S. favors those characteristics in a varying population that fit the specific
current, local environment
a.) no adv. to be pest. resistant until pesticides used
(2.Ex. Antibiotic Resistant Bacteria)
Concept 14.4: Microevolution is a Change in a Population’s Gene Pool
(Darwin needed Mendel’s principles to explain how variations that are selected for pass to the next gen.
Union of genetics with evol. biology focuses on change within a population)
I. Populations and Their Gene Pools
A. Population is the smallest level at which evolution can occur
B. Gene Pool = all the alleles (alternative forms of genes) in all the individuals that make up a
population
1. Reservoir for next gen. to draw its genes – where variation is stored
a. Ex. Wild mustang gene pool – vast variation in color, etc. (See fig. 14.23, p. 311)
1.) ↑ by genetic recomb during meiosis and fert.
II. Changes in Gene Pools
A. N. S. not random – always selects variations w/ greater chance for survival + repro. success
1. Some alleles may become more common than others = change in frequency of alleles
a. Usually expressed as a decimal or % (See Fig. 14.24, p. 311)
B. Microevolution = evolution on the smallest scale—a generation-to-generation change in the
frequencies of alleles within a population.
1. Merges Mendel’s and Darwin’s theories
2. Opposite condition = not evolving = no change in allele freq. in a pop.
a. Hardy – Weinberg Equilibrium = populations that do not undergo change to their
gene pool
1.) rare in nature – but provides “baseline” to detect when evol. is occurring
C. Two Main Factors can change gene pool
1. Genetic Drift
2. Natural Selection
III. Genetic Drift = change in the gene pool of a population due to chance
A. Ex. Wildflower Pop. – See Fig. 14.25, p. 312
1. Mainly chance causing which plants reprod. – no white alleles left by 3rd gen. = change in
allele freq.
B. All pop. subject to some genetic drift
1. Genetic Drift has more impact on smaller pop. – Read p. 312
C. Major Effects from Genetic Drift due to:
1. The Bottleneck Effect = Read p. 312
a. caused by natural disasters
b. results in reduced gene pool size with some alleles more freq, and some alleles lost
from gene pool (See Fig. 14.26, p. 312)
c. can reduce the ability of a population to adapt to environmental change
1.) Ex. Cheetah – 1 or more bottlenecks in last 10,000 years
a.) ↓ pop. size - concerned that with relatively little variation in their gene
pools, the cheetah populations may not be able to resist disease or adapt
to other environmental challenges (see fig. 14.27, p. 313)
2. Founder Effect = Genetic drift in a new colony when a few individuals colonize an isolated
island, lake, or some other new habitat.
a. smaller the colony, the less its genetic makeup will rep. gene pool of the lg. population
b. Ex. Galapagos Island finches, etc.
IV. Gene Flow and Mutation –also play roles in changing a gene pool
A. Gene Flow = exchange of genes with another population
1. occurs when fertile individuals or their gametes (sex cells) migrate between populations
a. Ex. neighboring field of wild flowers has pollen for white allele blown in by wind to
other pop., ↑ white allele freq.
2. Tends to reduce genetic diff. b/t populations – can even lead to a common gene pool
B. Mutation = a change in an organism's DNA
1. If carried by a gamete, it enters the pop. gene pool
2. N.S.and/or genetic drift – can influence if the freq. of a new mutation ↑ in a pop.
a. Ex. albino deer – read p. 314 – allele for albinism likely to ↑ in pop, or ↓ in pop.?
Why?
******3. Mutation plays a key role in evolution as the original source of the genetic variation that
is the raw material for natural selection
a. esp. in asexually repro species – ex. bacteria
b. sex. repro – source of variation more often allele shuffling
V. Natural Selection and Fitness
A. Only Natural Selection leads to Adaptation or “Fitness” for Envir.
1. Genetic drift, gene flow and mutation do not nec; lead to adaptation
2. N.S. – blend of chance (mutations + sex. recom. of alleles and sorting (reprod. success in pop)
B. Survival of the Fittest – not a direct contest b/t indiv., but competition that is usually less dramatic
1. Ex. wing color of moths for camo., flower color or frag. more attractive to pollinators, etc.
2. Fitness = the contribution that an individual makes to the gene pool of the next generation
compared to the contributions of other individuals = biological definition
a. prod. of healthy, fertile offspring all that matters in N. S..
VI. Return to the Galapagos (Read p. 315 – 316, and See Fig. 14.31)
A. Recent documentation of changes in allele frequencies in pop. of ground finch due to changes in
envir. – seed size
B. Shows that N. S. can occur quickly enough to be documented in a person’s lifetime
1. Darwin thought it was too slow for that
Concept 14.5: Evolutionary Biology is Important in Health Science
(Can we explain some common health problems in an evolutionary context? Maybe – see the 2 examples
below)
I. Natural Selection and Sickle Cell Disease (Read p. 317-318)
A. Caused by recessive allele
1. 1/25 in some African pop. have disease
2. Symptoms – sickle shaped RBC’s, (See Fig. 14.32, p. 317) pain, damage to organs, general
weakening (anemia), even death
3. Carriers: have 1 allele
4. Why so common in Afr. Pop?
a. Sickle cell allele can have benefits in tropics – resistance to malaria
1.) adv. in areas where malaria is a major cause of death in infants
5. See Fig. 14.33, p. 318 – allele freq. highest in areas where malaria parasite most common
a. freq as high as 1/3 people have the allele
b. only 4% homozygous and have sickle cell disease, but 32% carriers resis. to malaria
c. N. S. maintains this higher freq. of the allele since survival adv. to resist malaria
II. Evolution of Antibiotic Resistance in Bacteria (Read p. 318 -319)
A. Antibiotics = Medicines that kill or slow the growth of bacteria
1. widespread use has caused evol. of bacterial pop. that are antibiotic resistant
2. How? Can you explain it? (Think about the pesticide resistant insects…)
B. Huge problem in public health!
1. Ex. New York City – some tuberculosis-causing bacteria that are resistant to all 3 previously
used antibiotics (See Fig. 14.34, p. 319)
a. people with the strain have no better chance of survival than patients 100 years ago!
2. Effects how doctors prescribe antibiotics now – less likely to use unless absolutely necessary
C. Principles of Evolution – helps people understand human interactions with the living world today