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Principles of Biology - Biology 111
Winter Quarter
Lake Tahoe Community College
Instructor: Sue Kloss
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Ch. 13 - How Populations Evolve
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Ch. 13 - How Populations Evolve
Intro - Blue Footed boobies - diving bird species native to the Galapagos Islands.
A. Physical features that help them survive in their environment
1. large, webbed feet - great for propelling while diving for fish - not great on land
2. streamlined body and bill
3. large tail for pulling out of 80 foot dives in water
4. nostrils that close in water
5. glands to stay afloat and manage salt intake
6. gland at tail to secrete oil for waterproofing
7. gland in eye to control salt, draining it to nasal cavity - clears by shaking
B. Most benefits are tradeoffs - good for some things, hindrance in others - like big feet
C. Evolutionary Adaptations - inherited traits that enhance an individual’s ability to survive and
reproduce in a particular environment
D. Evolution - inherited change in organisms over time (Fig 13.1)
1. results in adaptations (Fig. 13.2)
I. Evidence of Evolution
A. A sea voyage helped Darwin frame his theory Ideas of evolution prior to Darwin
1. Widely held view that all organisms on earth were less than 6000 yr old, static in form
2. Mid 1700s, fossils were recognized as old remnants. French naturalist George Buffon
suggested that earth might be much older than 6k yrs.
3. Jean Lamarck - came up with idea of inheritance of acquired characteristics - mechanism
erroneous
a. giraffes evolved bc they stretched their necks to get food, and passed it along
b. Lamarck correctly inferred that environment is a factor in inheritance
c. no one has found evidence that the env. can modify traits in an individual that can be
passed on
4. Charles Lyell - uniformitarianism. Up till that time, people thought the earth was 6000 yrs old,
since people had been recording history or making it for their time on earth Uniformitarianism
suggested that earth was much older - geological evidence
a. laws of physics and chemistry remain the same throughout the history of earth,
including the present
b. past geological events occurred by processes similar to those we observe today
c. important in establishing that events on the earth occur in predictable ways due to
causes we can generally explain
B. Darwin - 23 yr old naturalist on the Beagle, a research ship mapping the coast of S. America. (Fig.
13.3.) He found fossil evidence of sea animals in the Andes Mountains, and came to believe that slow
natural processes like the growth of the mtns through earthquakes could help account for those marine
animals’ presence. Strongly influenced by reading Lyell
1. Galapagos islands flora and fauna - differences and similarities with mainland life inspired
development of his theories of evolution (Fig. 13.4)
2. His book “On the Origin of Species by Means of Natural Selection, or the Preservation of
Favoured races in the Struggle for Life” sold 1250 copies, the whole first printing, on its first day.
It was and is very controversial. Origin of Species included an “avalanche of reasoning and
evidence”. Supporting “descent with modification” = change over time
C. (Fig. 13.7) evidence for perpetual change in found in fossil record.
1. fossil - remnant of past life
a. organic elements decay
b. mineralized parts - shells, bones, teeth may remain
c. casts
d. complete - tar pits, glaciers, amber
e. petrification- minerals dissolved in groundwater replace organic material in tissue
f. sedimentary deposits - fish, amphibians, reptiles, mammals and birds
1. older deposits contain older fossils - documentation of change over time
a). changes in skull size and shape as mammals evolved from reptiles
b). whales evolved from 4 legged land mammals - (Fig 13.8)
c). evolution of modern horse
2. record of changing geologic conditions over earth - distribution of land and sea
D. Evidence for Darwin’s theories: Biogeography - geographic distribution of species –
1. continent of austraila home to many unique species, bc of isolation (Fig 13.9)
2. environment of Galapagos more like S. Pacific islands, animals more like S. American
animals, as Darwin noted
E. Comparative Anatomy, also known as homology, and comparative embryology help explain Darwin’s
theory of common descent
1. homologs - (Fig. 13.10) also called homologous structures.
2. Comparative embryology - closely related organisms often have similar stages in their
embryonic development. (embryo = early developmental stages in multicellular organism)
a. one sign vertebrates appeared from a common ancestor- embryos of all known
vertebrates have gill pouches in their throats. At this stage, all vertebrates look more alike
than different (Fig. 13.11)
3. molecular biology - related individuals have greater similarity in their DNA than unrelated
individuals (Fig. 13.12) the polypeptide chain in hemoglobin, which carries O2 in blood. The chain
of amino acids in this polypeptide differs by only a little in humans and monkeys, much more in
humans and lampreys. this agrees with fossil and embryological evidence.
4. phylogenys are constructed to explain patterns of descent
II. Darwin’s theories and the Modern Synthesis
A. Darwin proposed natural selection as the mechanism of evolution (fig 13.13)
1. Darwin recognized that species tend to produce excessive numbers of offspring – (fig 13.14)
2. influenced by Malthus- population growth rate would outstrip resources. Darwin applied this to
all organisms
3. struggle for existence among individs in a population
4. only a tiny fraction complete life cycle and reproduce
5. Darwin also noted that individuals have various traits, (Fig. 13.15) and
6. many traits are inherited.
7. since resources are limited, every population has individs more well suited to environment
than other individuals
8. those will leave more offspring
9. Put another way, differential reproductive success (natural selection) is how the
environment “chooses” those individuals most well suited to life there
10. humans were well familiar with artificial selection - human manipulation of plants and
animals to produce traits we favor
B. Populations are units of evolution (Fig 13.16)
1. population - group of individuals of same species living in same place and time, potentially
interbreeding
2. smallest unit that can evolve
3. evolution - change in heritable traits over time - eg. pesticide
4. individuals do not evolve
5. Modern Synthesis melds population with evolution, uses population genetics as a basis for
understanding evolution (modern synthesis = genetics with evolutionary biology)
6. species - group of populations of the same species that have the physical capability to
interbreed
7. If little interbreeding occurs between populations in different geographic areas, little gene
flow occurs
8. will probably differentiate more over time
9. many pops are continuous
D. Microevolution is a change in a populations gene pool (allele frequency) over time
1. gene pool = total collection of genes in a population
2. consists of alleles - alternative forms of the same gene
3. most genes have 2 or more alleles
4. in the body, most organisms have a gene from each parent
a. homozygous
b, heterozygous
5. when allele frequencies change over time, this is called microevolution
6. Several causes
a. altered by genetic drift (fig 13.20Campbell) -
E.
F.
G.
H.
1. bottleneck effect (Fig. 13.21)
2. . founder effect - genetic drift in a new colony
b. migration, or gene flow - reduces differences btn pops, introduces new genes
c. natural selection - most likely factor to result in adaptation
d. mutation - random change in DNA- only force that creates new alleles
Hardy – Weinberg Equilibrium; allele frequencies in a pop will stay the same unless acted upon by an
outside force. Again, these forces are: (same as above- changes to allele frequency)
1. genetic drift
2. gene flow
3. natural selection
4. mutation
Adaptive changes result when natural selection favors certain designs
1. individuals are all varied in a population
2. Some individuals leave more offspring than others – this is called fitness, or Darwinian fitness
a. this is what “survival of the fittest” refers to (Fig. 13.25)
3. If environment changes, traits of successful individuals will probably change
Three general outcomes of natural selection (Fig. 13.26)
1. stabilizing selection
2. directional selection
3. diversifying selection
The evolution of microbial resistance to antibiotics is a serious public health concern.
Homework questions (optional)/Lesson Objectives ch13
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Describe 4 adaptations that help blue footed boobies survive
How did Darwin’s voyage on the Beagle influence his thought?
What other thinkers of the time also influenced Darwin’s thought, and how?
List and explain 4 ways that fossils form. Give examples.
How does the fossil record provide some of the strongest evidence for evolution?
How do biogeography, comparative anatomy, comparative embryology, and molecular biology document
evolution?
Describe Darwin’s assumptions in developing concept of natural selection.
Describe 2 examples of natural selection that are known to occur.
What are 3 key points in how natural selection works?
Describe adaptation.
Distinguish between a species and a population
Describe the modern synthesis.
Explain how microevolution occurs.
Explain how bottleneck effect, founder effect, gene flow, and mutation influence microevolution.
Explain why only some variation is heritable.
Describe the Hardy Weinberg equilibrium, and explain what conditions must be met for Hardy-Weinberg to be
upheld in a population.
What is Darwinian fitness?