CHAPTER 16: DARWINS THEORY Natural Selection and Evolution
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The eight characteristics of living things? 1. Living things
are based on a universal genetic code (DNA) 2. Living things grow
and develop 3. Living things respond to their environment
(stimulus) 4. Living things reproduce 5. Living things maintain a
stable internal environment (homeostasis) 6. Living things obtain
and use material and energy (metabolism) 7. Living things are made
up of CELLS 8. Taken as a group, living things evolve over
time
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InferenceInferenceHypothesisHypothesis A logical interpretation
based on what scientists already know. A scientific explanation for
a set of observations that can be tested in ways that support or
reject it. A possible explanation for what you expect to happen Ex.
Plants will grow toward a source of light. Making Inferences and
Forming Hypotheses:
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Scientific Theory A well-tested explanation that unifies a
broad range of observations and hypotheses Explains a broad set of
observations about the natural world. Is supported by evidence and
data Provides a set of principles that can be used to make testable
predictions and hypothesis. The meaning of the word theory in daily
life is different from its meaning in science A scientific theory
is NOT a hunch
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Cell Division and Reproduction Asexual Reproduction Sexual
Reproduction A single parent Genetically identical offspring
Advantage: Simple, efficient, & effective way for an organism
to produce a large number of offspring. Disadvantage: may not be
able to adapt to change Fusion of two sex cells one from each of
two parents Genetically diverse offspring Advantage: Genetic
diversity helps ensure survival of species when environment changes
Disadvantage: Process takes a long time
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Genes and Alleles Each of the traits Mendel studied was
controlled by one gene that occurred in two contrasting varieties.
These gene variations produced different expressions, or forms, of
each trait. The different forms of a gene are called alleles.
Dominant = Form of a gene that is expressed even if present with a
contrasting recessive allele. Example: BB or Bb A = dominant allele
Recessive = Form of a gene (allele) that is only expressed in the
homozygous state. Example: bb
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Homozygous (Purebred) vs. Heterozygous (Hybrid): Homozygous =
Organism that has two identical alleles for a particular trait.
(Ex: AA, bb, CC, dd) Heterozygous = Organism that has two different
alleles for the same gene. (Ex: Aa, Bb, Cc, Dd)
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Genotype vs. Phenotype: Genotype: Genetic make-up of an
organism (Ex: Aa, BB, cc) Phenotype: Physical characteristics of an
organism (Ex: flower color, eye color)
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Types of Cells Affected Germ Mutation - affects a reproductive
cell (gamete or sperm/egg) Does not affect the organism Passed to
offspring Somatic Mutation affects body cells (all cells except
gametes) Not passed to offspring
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Polygenic Traits Traits controlled by two or more genes are
said to be polygenic traits. Polygenic means many genes. Polygenic
traits often show a wide range of phenotypes. The variety of skin
color in humans comes about partly because more than four different
genes probably control this trait.
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Segregation During gamete formation, the alleles for each gene
segregate from each other, so that each gamete carries only one
allele for each gene.
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Synapsis and Tetrads During synapsis, the homologuous
chromosomes pair up, forming a structure called a tetrad, which
contains four chromatids.
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Crossing Over As homologous chromosomes pair up and form
tetrads, they undergo a process called crossing-over. First, the
chromatids of the homologous chromosomes cross over one another.
Then, the crossed sections of the chromatids are exchanged.
Crossing-over is important because it produces new combinations of
alleles in the cell.
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Darwins Epic Journey Charles Darwin was born in England on
February 12, 1809. He grew up at a time when the scientific view of
the natural world was shifting dramatically. Geologists were
suggesting that Earth was ancient and had changed over time, and
biologists were suggesting that life on Earth had also changed. The
process of change over time is called evolution. Darwin developed a
scientific theory of biological evolution that explains how modern
organisms evolved over long periods of time through descent from
common ancestors.
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Darwins Epic Journey Darwin was invited to sail on the HMS
Beagles five-year voyage mapping the coastline of South America.
Left from England, sailed around South America, across Pacific,
around Australia and Africa, and back to England Darwin was the
ships naturalist he planned to collect specimens of plants and
animals on the voyage. Most famous for observations made at
Galapagos Islands No one knew it, but this would be one of the most
important scientific voyages in history.
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Darwin noted 3 patterns of biodiversity: 1.Species vary
globally 2.Species vary locally 3.Species vary over time 16-1
Darwins Voyage of Discovery
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Different, yet ecologically similar animal species inhabited
separate, but ecologically similar, habitats around the globe Ex)
flightless birds: rheas, ostriches and emus 1. Species vary
globally Native to Africa Largest of 3 Native to S.America Native
to Australia Slightly Larger than Rhea Rhea OstrichEmu
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Different, yet related animal species occupied different
habitats within a local area (tortoise shell shape - Galapagos) 2.
Species vary locally
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3. Species Vary Over Time Darwin also collected fossils, which
are the preserved remains or traces of ancient organisms. Darwin
noticed that some fossils of extinct animals were similar to living
species.
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Fossils found in Towamencin While construction crews from Allan
A. Myers (AAM) have been building stormwater basins and doing
excavations by Exit 31 in Lansdale as part of the ongoing Northeast
Extension road-widening project, geologists from Kutztown
University have uncovered something even bigger hidden among the
massive slabs of rock. Fossils Found in Turnpike Excavation article
on The Reporter Fossils Found in Turnpike Excavation Fossils Found
in Turnpike Excavation pictures Fossils Found in Turnpike
Excavation
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Lamarcks Theory of Evolution Inheritance of Acquired Traits
Acquired traits could be inherited For example: If you spent your
life lifting weights, then your children would inherit large
muscles.
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Lamarcks Theory of Evolution Evaluating Lamarcks Theory He was
wrong in several ways He didnt know how traits were inherited He
did realize that organisms adapt to their environment.
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Artificial Selection To find an explanation for change in
nature, Darwin studied change produced by plant and animal
breeders. Breeders knew that individual organisms vary, and that
some of this variation could be passed from parents to offspring
and used to improve crops and livestock selective breeding. For
example, farmers would select for breeding only trees that produced
the largest fruit or cows that produced the most milk. Over time,
this selective breeding would produce trees with even bigger fruit
and cows that gave even more milk.
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Artificial Selection Darwin called this selective breeding
process artificial selection, a process in which nature provides
the variations, and humans select those they find useful. Darwin
put artificial selection to the test by raising and breeding plants
and fancy pigeon varieties. BBC Darwin's Pigeons (2:18) Darwin's
pigeons described by Randal KeynesDarwin's pigeons described by
Randal Keynes (7:49)
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Artificial Selection Darwin had no idea how heredity worked or
what caused heritable variation, but he did know that variation
occurs in wild species as well as in domesticated plants and
animals. Before Darwin, scientists thought variations among
individuals in nature were simply minor defects. Darwin recognized
that natural variation was very important because it provided the
raw material for evolution. Natural variation = differences among
individuals of a species When Darwin published his scientific
explanation for evolution, it changed the way people understood the
living world.
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Population Growth Malthus observed that babies were being born
faster than people were dying. If population continued to grow
there would be insufficient food and space. In plants or animals
most of the offspring die Only those who survive can reproduce What
determines which ones will survive and reproduce?
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The Struggle for Existence After reading Malthus, Darwin
realized that if more individuals are produced than can survive,
members of a population must compete to obtain food, living space,
and other limited necessities of life. Darwin described this as the
struggle for existence.
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Variation and Adaptation Darwin knew that individuals have
natural variations among their heritable traits, and he
hypothesized that some of those variants are better suited to life
in their environment than others. Any heritable characteristic that
increases an organisms ability to survive and reproduce in its
environment is called an adaptation.
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Three types of adaptations that involve body parts or
structures : 1.Structural physical features of an organism Ex: long
tongue to get food, sharp teeth, mimicry, camouflagecamouflage
2.Behavioral actions an organism takes Ex: migration, tracking
prey, storing nuts, growing towards light 3.Physiological
functioning or biochemical processes Ex: venom, ink of octopus,
protein in web, respiration rate, digestive enzyme, blood
clotting
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Mimicry Scarlet king snake exhibits mimicry - an adaptation in
which an organism copies, or mimics, a more dangerous organism.
Although the scarlet king snake is harmless, it looks like the
poisonous eastern coral snake, so predators avoid it, too. Non
poisonous snakes will also rattle their tale and flatten their head
to look poisonous to a predator.
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Mimicry Monarch butterfly - is toxic and very nasty to eat. Its
bright orange coloration is a warning to birds to leave it alone.
Non-toxic viceroy butterfly has developed colors and wing patterns
that are very similar to those of the monarch most birds wont take
a chance by taste-testing it
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Camouflage An adaptation that allows an organism to blend into
its background and avoid predation.
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Variations vs. Adaptations Variations differences that exist
within a population that may have no effect on fitness Ex: length
of your thumb Adaptations a variation that all members of a
population have inherited because that trait improves fitness Ex:
an opposable thumbs
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Sources of variation Sources of variation: Mutations individual
genes change Ex: ATC AGC Events during meiosis during meiosis,
chromosomes get mixed up (crossing over) in making eggs & sperm
Random fusion of gametes which sperm fertilizes which egg
determined by chance
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Survival of the Fittest According to Darwin, differences in
adaptations affect an individuals fitness. Fitness describes how
well an organism can survive and reproduce in its environment.
Individuals with adaptations that are well-suited to their
environment can survive and reproduce and are said to have high
fitness. Individuals with characteristics that are not well-suited
to their environment either die without reproducing or leave few
offspring and are said to have low fitness. This difference in
rates of survival and reproduction is called survival of the
fittest. In evolutionary terms, survival means reproducing and
passing adaptations on to the next generation.
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Natural Selection Darwin named his mechanism for evolution
natural selection because of its similarities to artificial
selection. Natural selection is the process by which organisms with
variations most suited to their local environment survive and leave
more offspring. In natural selection, the environment not a farmer
or animal breeder influences fitness.
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Natural Selection Well-adapted individuals survive and
reproduce. From generation to generation, populations continue to
change as they become better adapted, or as their environment
changes. Natural selection acts only on inherited traits because
those are the only characteristics that parents can pass on to
their offspring.
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Natural Selection Natural selection does not make organisms
better. Adaptations dont have to be perfectjust good enough to
enable an organism to pass its genes to the next generation.
Natural selection also doesnt move in a fixed direction. There is
no one, perfect way of doing something. Natural selection is simply
a process that enables organisms to survive and reproduce in a
local environment.
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Natural Selection If local environmental conditions change,
some traits that were once adaptive may no longer be useful, and
different traits may become adaptive. If environmental conditions
change faster than a species can adapt to those changes, the
species may become extinct.
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Common Descent Natural selection depends on the ability of
organisms to reproduce and leave descendants. Every organism alive
today is descended from parents who survived and reproduced. Darwin
proposed that, over many generations, adaptation could cause
successful species to evolve into new species. He also proposed
that living species are descended, with modification, from common
ancestorsan idea called descent with modification. According to the
principle of common descent, all speciesliving and extinctare
descended from ancient common ancestors.
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Darwin published his findings in 1859 in a book entitled The
Origin of Species by Means of Natural Selection. He was motivated
to publish his book in 1859 because Alfred Wallace had
independently come up with the same conclusions 16-3 Darwin
Presents His Case
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The Age of Earth Evolution takes a long time. If life has
evolved, then Earth must be very old. Hutton and Lyell argued that
Earth was indeed very old, but technology in their day couldnt
determine just how old. Geologists now use radioactivity to
establish the age of certain rocks and fossils. Radioactive dating
indicates that Earth is ~4.5 billion years old - plenty of time for
evolution by natural selection to take place.
1. Fossil Evidence Fossils - the remains of past life Ex:
shells, bones, teeth, imprints Tell us - age, habitat, diet, &
lifestyle of organisms. Record is incomplete many organisms leave
no fossils behind
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2. Anatomical Evidence Homologous Structures Darwin proposed
that animals with similar structures evolved from a common ancestor
with a basic version of that structure. Structures that are shared
by related species and that have been inherited from a common
ancestor are called homologous structures. Homologous structures
are similar in structure because they develop from same tissues
early in development may or may not have different functions. Bones
of vertebrate forelimbs
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Homologous Structures
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2. Anatomical Evidence Analogous Structures The clue to common
descent is common structure, not common function. A birds wing and
a horses front limb have different functions but similar structures
(homologous structures). Body parts that share a common function,
but not structure, are called analogous structures. Analogous
structures are used for the same purpose but are not due to a
common ancestor. The wing of a bee and the wing of a bird are
analogous structures.
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Analogous vs. Homologous Structures
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Vestigial Structures Not all homologous structures have
important functions. Vestigial structures are inherited from
ancestors, but have lost much or all of their original function due
to different selection pressures acting on the descendant. The
hipbones of bottlenose dolphins are vestigial structures. In their
ancestors, hipbones played a role in terrestrial locomotion.
However, as the dolphin lineage adapted to life at sea, this
function was lost. The human tailbone and appendix are vestigial
structures. Cormorant flightless bird
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Vestigial Structures
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Evolution Evidence Vesitgial Structure Video in dropbox
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3. Embryology Similar patterns of embryological development
provide further evidence that organisms have descended from a
common ancestor. the more similar the embryos are at certain stages
of development, the more closely related they are thought to be.
Which one is a Chicken, Fish, Human, Rabbit, Salamander,
Turtle??????
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Embryology - the more similar the embryos are at certain stages
of development, the more closely related they are thought to
be
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4. Biochemical Evidence Universal genetic code organisms use
the same triplet code and the same 20 amino acids in proteins All
organisms have certain organic molecules in common. 1. Hemoglobin -
carries oxygen in blood 2. Cytochrome c - protein for cell
respiration found in almost all living cells 3. HOX genes control
development Genes Control Body Segmentation PBS - 13:45
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Significance of biochemical differences
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5. Direct Observation Direct observation weve seen evolution
occur in cases like: The Grants studies of finches on Daphne Major
in the Galapagos (35 yrs) Bacteria becoming resistant to
antibiotics Insects that become resistant to pesticides