Download Steps in Darwin`s Theory

 Make a list of some characteristics that birds have that
could provide information about their diets
 Modern evolutionary theory began when
Darwin presented evidence that evolution
happens and offered an explanation of how
evolution happens
 Darwin’s experience provided him with
evidence of evolution at work
 Darwin was influenced by ideas from the
fields of natural history, economics and
geology
 Evolution is the process by which species may
change over time
 Modern evolutionary theory began when Darwin
presented evidence that evolution happens and
offered an explanation of how evolution happens
 Many scientists since Darwin have tested and
added to his ideas. Most of Darwin’s ideas,
including his main theory, remain scientifically
supported
 In Darwin’s time, most people did
not think that living things had
changed over time.
 Many doubted that Earth itself
had ever changed.
 Darwin saw evidence of gradual
change
The Voyage of the Beagle
 Darwin’s first evidence: gathered during a global
voyage on a ship called the Beagle
 As a naturalist, Darwin collected
natural objects from each place he
visited. He also collected fossils and
noticed that they were similar to, but
not the same as, living things
The Voyage of the Beagle
 Darwin visited the Galapagos Islands in the Pacific Ocean
 Collected several different species of birds called finches
 Each of the finches are very similar, but differences can be
seen in the size and shape of the beak
 Each finch has a beak that seems suited to the finch’s usual
food
The Voyage of the Beagle
 Darwin noticed that many of the islands’ plants and
animals were similar, but not identical, to the plants
and animals he saw on South America
 Darwin proposed Galapagos species descended from
species that originated in South America
The Voyage of the Beagle
 He suggested that all of the finch species came from
one finch species that migrated from South America
 The descendant finches were modified over times as
different groups survived by eating different types of
food
 Darwin called such change descent with modification
 The selective breeding of domesticated plants and
animals
Population Growth
 Darwin simply applied the idea of human
overpopulation to all populations
 A population is all of the individuals of the same
species that live in a specific place
 Darwin saw that all kinds of organisms tend to
produce more offspring than can survive. So, all
populations must be limited by their environment
Geology and an Ancient Earth
 In Darwin’s time, scientists had interest in the study of
rock landforms, and thus began geology
 Geologists study fossil and rock layers
 The fossils in rock layers showed
differences in species over time
and that many species from the
past differed from those of the
present
Geology and an Ancient Earth
 Most scientists and geologists
thought that changes in the
past occurred suddenly
 Others thought that geologic
processes work gradually and
constantly
 This fit well with Darwin’s
observations and showed that
Earth's history was long enough
for species to have evolved
gradually
 French scientist Jean Baptiste
Lamarck proposed an
explanation for how organisms
may change over generations
 Lamarck noticed that each
organism was usually well
adapted to its environment. He
proposed that organisms change
over time as they adapt to
changing environments
 Lamarckian Inheritance
 Changes due to use or disuse of a characteristic would be
passed on to offspring and inherit these changes
 Lamarck had an incorrect idea about inheritance and
this idea was eventually disproved
 Modern evolutionary theory began when Darwin
presented evidence and explained how evolution could
occur
 Lamarck’s evidence for evolution seemed correct
during his time, but it was later disproved
“Nothing in biology makes
sense except in the light of
evolution”
-Theodosius Dobzhansky
Journal #2: What do you think this quote
means? What is your personal opinion
about this quote? (Response must be a
minimum of 5 sentences)
 What beliefs do you more closely identify
with Lamarck or Darwin?
 Remember responses must be at least 5
sentences.
 Having trouble? Review your notes, write
out the beliefs both Lamarck and Darwin
had then support your argument.
 Explain how studying fossils can tell
you how an organisms lived.
 Also, are you superstitious?
 Darwin’s theory predicts that over time, the
number of individuals that carry
advantageous traits will increase in a
population
 Darwin presented a unifying explanation for
data from multiple fields of study
 Every living organism has the potential to produce
many offspring, but not all of those offspring are
likely to survive and reproduce
 Darwin formed a key idea:
 Individuals that have traits that are better suited
to their environment are more likely to survive
and in turn produce more offspring
 Natural selection is the process by which
individuals that are better adapted to their
environment survive and reproduce more
successfully than less well adapted
individuals do
 Evolution is a change in the inherited
characteristics of a population from one
generation to the next
Steps in Darwin’s Theory
 Darwin’s theory predicts that over time, the
number of individuals that carry
advantageous traits will increase in a
population
 This can be summarized in four logical steps
Steps in Darwin’s Theory
 Step 1: Overproduction
 Every population is capable of producing
more offspring than can possibly survive
 Step 2: Variation
 Variation exists
within every
population. Much of
this variation is in the
form of inherited
traits
Steps in Darwin’s Theory
 Step 3: Selection
 In a given environment, having a particular trait
can make individuals more or less likely to
survive and have successful offspring. So, some
individuals leave more offspring than others do
 Step 4: Adaptation
 Over time, those traits that improve survival and
reproduction will become more common
Selection and Adaptation
 Darwin’s theory explains why living things vary in
form yet seem to match their environment
 Each habitat presents unique challenges and
opportunities to survive and reproduce
 Each species evolves because of the “selection” of
those individuals that survive the challenges or
make best use of the opportunities
 Natural selection can alter variation in a
population in three ways:
 Stabilizing selection
 Favors intermediate phenotypes
 Directional selection
 Acts against individuals at one of the
phenotypic extremes
 Disruptive selection
 Favors individuals at both extremes of the
phenotypic range
Selection and Adaptation
 An adaptation is an inherited
trait that is present in a
population because the trait
helps individuals survive and
reproduce in a given
environment
 Darwin's theory explains
evolution as a gradual process of
adaptation
 Darwin’s book On the
Origin of Species by
Means of Natural
Selection presented
evidence that evolution
happens and offered a
logical explanation of
how it happens
 Video
 Is natural selection the same as
evolution? Why or why not?
 Journal #3: What beliefs do you more
closely identify with Lamarck or Darwin?
 Journal #4: Do you think natural selection
actually occurs in our world? Do you think
it is the means by which organisms evolve?
 Journal #4: Do you think natural
selection actually occurs in our world?
Do you think it is the means by which
organisms evolve?
 Think about a dog or cat, compare their way
of movement to yours.
 Compare the bone structure of your arms
and legs compared to that of a dog or cat
Biogeography
 Biogeography is the
study of the locations
of organisms around
the world
 Sometimes geography
separates populations.
For example, a group of
organisms may become
separated into two
groups living on two
different islands
http://www.pbs.org/wgbh/nova/evolution/evolution-action-salamanders.html
Biogeography
 Species tend to be more closely related to other species
from the same area than to other species within the same
way of life but living in the same area
 Geologists and biologists have found that the movement
of land in Earth’s past helps explain differences in living
and fossil organisms
The Fossil Record
 You can infer past
events by looking
at fossils, traces of
organisms that
lived in the past
Anatomy
 Darwin helped explain differences in organisms
through bodily structure, or anatomy
 Many internal similarities are best explained by
evolution and are evidence of how things are
related
 The hypothesis that all vertebrates descended from
a common ancestor is widely accepted
Anatomy
 The forelimbs of many vertebrates are composed of the
same basic group of bones
Anatomy
 This pattern of bones is thought to have originated
in a common ancestor
 The bones are examples of homologous
structures, characteristics that are similar in two or
more species and that have been inherited from a
common ancestor
 Many vertebrates have common embryonic structures
 http://www.pbs.org/wgbh/nova/evolution/guess-
embryo.html
 Natural selection favors positive
mutation
 Genes can change by mutation
and that such change can make
new varieties appear
 Natural selection may “select
against” some varieties and so
“favor” others
 Camouflage adaptations that
evolved in different environments
 A comparison of DNA shows
that some species are more
genetically similar than others
 These comparisons, like
anatomy, are evidence of
hereditary relationships
among the species
Gene that encodes leptin in humans,
chimps and gorillas. 250 nucelotides,
5 differences
 Darwin’s theory of evolution by natural selection
predicts that over time, the number of individuals that
carry advantageous traits will increase in a population
 Darwin’s work had three major principles: evidence of
evolution, a mechanism for evolution, and the
recognition that variation is important
 Begin reading news article and answering
the following questions:
 How is TB usually treated?
 What is TB? How many people does it
affect?
 Why is antibiotic resistant TB so
dangerous?
 How has Darwin’s theory
been updated?
 At what scales can
evolution be studied?
 Discoveries made since
Darwin’s time, especially
in genetics, have been
added to his theory to
explain the evolution of
species.
 The first major advance beyond Darwin’s ideas was
the rediscovery, in 1900, of Mendel’s Laws of
Heredity
 Scientists continued to weave Darwin’s theory
together with newer studies of fossils, anatomy,
genetics, and more
 DISCOVERED: long lost fossils from Darwin’s
journey around the world (Jan. 16, 2012)
Remaining Questions
 Can an individual evolve?
 Darwin correctly inferred that individuals
do not evolve. They may respond to
outside forces, but individuals do not pass
on their responses as heritable traits.
Rather, populations evolve when natural
selection acts (indirectly) on genes.
Remaining Questions
 Is evolution the survival of the fittest?
 Natural selection can act only on the
heritable variation that exists in the
population. Chance variations do not always
provide the best adaptation for a given time
and place. So, evolution does not always
produce the “fittest” forms, just those that
“fit” well enough to leave offspring.
Remaining Questions
 Is evolution predictable?
 Evolution sometimes results in larger or
more complex forms of life, but this result
cannot be predicted. Many forms of life
are simple yet successful. Mostly,
scientists cannot predict the exact path
that evolution will take.
 Because it affects every aspect of biology,
scientists can study evolution at many scales
 Microevolution
 Macroevolution
 Microevolution refers to evolution as a
change in the genes of a population
 Macroevolution refers to the appearance of
new species over time
 Five major processes can affect the kinds of
genes that will exist in a popualtion
 (1) Natural selection
 (2) Migration
 (3) Mate Choice
 (4) Mutation
 (5) Genetic Drift
 (1) Coevolution
 Organisms are part of one
another’s environment, so
they can affect one
another’s evolution
 (2) Adaptive Radiation
 Over time, species may
split into two or more lines
of descendents. As this
splitting repeats, one
species can give rise to
many new species
 (3) Extinction
 If all members of a species die off or simply fail to
reproduce, they are said to be extinct
 (4) Gradualism
 Evolution generally
occurs uniformly and by
the steady and gradual
transformation of whole
lineages
 (5) Punctuated Equilibrium
 Most populations will show little change for most of their
geological history, and when evolution does occur, it is
localized in rare, rapid events of branching speciation
 Discoveries since Darwin’s time, especially in
genetics, have been added to his theory to explain
the evolution of species
 Because it affects every aspect of biology, scientists
can study evolution at many scales. Generally,
these scales range from microevolution to
macroevolution, with speciation in between
 The evolution of antibiotic resistance in bacteria is a
serious public health concern
 The excessive use of antibiotics is leading to the
evolution of antibioticresistant bacteria
 TB research in Russia:
http://www.pbs.org/wgbh/evolution/library/11/2/quic
ktime/e_s_6.html
 TB resistance in India:
http://www.huffingtonpost.com/2012/01/17/drugresistant-tuberculosis-india_n_1210361.html
 PBS Evolution
http://www.pbs.org/wgbh/evolution/students/index.h
tml
 Nova Evolution
http://www.pbs.org/wgbh/nova/evolution/