Download Natural Selection

Definition of Evolution
• Evolution is the process of change
through time.
• It is the process by which modern
organisms have descended from
ancient organisms.
Evolutionary Theory
• Is the unifying principle for all the
biological sciences.
• Provides an explanation for the
differences in structure, function, and
behavior among life forms.
• It includes the change in characteristics of
populations through generations. Thus
existing life forms have evolved from
earlier life forms.
Supporting Evidence
• Comparative Anatomy- this is the comparative
study of certain organisms showing similarities in
anatomical features.
• Comparative Embryology- comparison of early
embryonic development among groups of organisms
reveals similarities which suggest common ancestry.
More Supporting Evidence
• Comparative Cytology- Organelles are
structurally and functionally similar in
most divergent organisms, suggesting that
all living things are related to some
degree.
• Comparative Biochemistry- Many
different organisms have similar proteins
and enzymes, therefore their DNA must
be similar.
• Geologic Records- Fossils, the direct or
indirect remains of organisms preserved
in media, suggest links between modern
and ancient forms, as well as, divergent
pathways from common ancestors.
Charles Darwin- 19th century English Naturalist
• Proposed that evolution occurred as the result of Natural
Selection.
• Overproduction- within a population more offspring are
produced in each generation than can survive, because of
limitations of space and food.
• Competition- individuals compete for the available food and
opportunity to mate and reproduce.
• Variation- within each generation some individuals are better
fitted to survive than others because of variations in
characteristics.
• Survival of the Fittest- those individuals better fitted to
survive are more likely to live long enough to reproduce.
• Transmission of Favorable Traits (Reproduction)- offspring of
the fittest individuals will inherit the favorable variations that
enabled their parents to survive and reproduce.
• Evolution of Species (Speciation)- accumulation of favorable
variations will gradually lead to the appearance of new species
better adapted to their environment.
• Weakness in Darwin’s Theory is that it does not account for
genetic basis of variations. At the time, not much was known
about the mechanisms of genetic inheritance.
Natural Selection
• Natural selection is the process where inheritable
traits that make it more likely for an organism to
survive long enough to reproduce, become more
common over successive generations of a
population.
• It is a key mechanism of evolution.
• The Galapagos finches provide an excellent example
of this process. Among the birds that ended up in arid
environments, the ones with beaks better suited for
eating cactus got more food. As a result, they were in
better condition to mate. Similarly, those with beak
shapes that were better suited to getting nectar from
flowers or eating hard seeds in other environments
were at an advantage there. In a very real sense,
nature selected the best adapted varieties to survive
and to reproduce. This process has come to be
known as natural selection.
The Peppered Moth Study
An Example of Natural Selection!
Write similarities and
differences between these two
organisms!
Both have the Scientific Name:
– Biston betularia
Both are the same moth, commonly called
peppered moths. There is a story behind these
two different color variations. Click to find out
what happened!
• During the early
1800’s in
Birmingham,
England there were
dark and cream
colored moths.
However, almost
all peppered moths
were cream colored
because the tree
trunks were light
Would it be an advantage or colored.
Can you find the
moth on the tree
trunk?
disadvantage for the moth to
be light?
Something was happening in the cities
of England at this time,
What could that have been?
Industrial Revolution
•A greater number of factories were being
created, which meant more pollution!
Think/Pair /Share:
•What do you think was happening to the
peppered moths as a result of
industrialism?
WHAT’S HAPPENING!
Why did the frequency
of black moths increase
with the growing
industries?
• Around 1850, blackcolored peppered
moths started to
become more common
than cream, usually in
heavily industrialized
areas.
Darwin’s Theory of evolution
by natural selection suggests a
hypothesis.
White tree trunks were blackened
by heavy pollution from
factories.
Which Moth is better adapted to its environment?
Explain why?
•Perhaps dark moths
sitting on sootdarkened bark
escaped being eaten
by birds because it
was too hard for the
birds to see the dark
moths against the
dark background.
•Light-colored moths
would have stood out
against a dark
background and
would have been
easy prey for hungry
birds. Therefore,
more dark moths
survived.
This is an example of Natural Selection!
• Natural Selection- is a gradual
change in a species in response to
the demands of its environment.
Do Now:
• Write how the peppered moth
during the 1800’s was an example
of natural selection in action!
Charles Darwin
Background and Observations
Background Info.
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Darwin was born in England, Feb. 12, 1809.
Studied to become a physician, decided not to continue.
Studied to become a minister, decided not to continue.
Graduated college and at the age of 22, signed aboard the
HMS Beagle, as ship’s Naturalist. His job, as naturalist, was
to collect and study plant, animal, and geologic specimens
form the journey around the world.
The voyage began in December of 1831 and lasted 5 years.
Darwin kept extensive journals of his observations, studies,
and thoughts.
Darwin’s ideas on gradual change were influenced by the
evidence presented by Charles Lyell. Lyell stated that
gradual and observable geologic processes, such as erosion,
could explain the physical features of the Earth today.
Darwin was also influenced by James Hutton, who in 1785
proposed that the Earth was formed by geological changes
that occurred over a very long period of time .
• Darwin’s most intriguing finds occurred on the
Galapagos Islands.
• After returning home from his voyage, he
continued to wonder about the things that he had
seen.
• In 1838, he read an essay by Thomas Malthus, on
human population. Malthus stated in his essay,
that populations can grow much faster than the
rate at which food supplies and other resources
can be produced. Production of more individuals
than the environment can support lead to a
struggle for existence. This concept helped
Darwin to propose a mechanism for evolutionary
change.
• In 1844, Darwin outlined his ideas. In 1858, after
another British naturalist, Alfred Wallace, came to
the same conclusions about the basic mechanism
for evolutionary change, Darwin published his book,
The Origin of the Species by Means of Natural
Selection.
Darwin’s Observations
• There was an enormous number of species that
inhabited the Earth.
• Patterns of Diversity- he asked why similar
ecosystems were inhabited by different types of
species (why the grasslands of England had
rabbits, why the grasslands of Australia had
kangaroos?).
• Darwin wondered why so many organisms that were
once alive, were now preserved as fossil remains.
Why did these organisms cease to exist? How
were the fossils related to the living organisms?
• The Galapagos Islands- a small group of 16 islands 1000km
off the west coast of Equador. Darwin noticed that even
though the islands were relatively close together, they still
had very different climates.
The lowest were hot, dry, and barren
The highest had more rainfall, vegetation, and
more animal life.
• Darwin noticed that the characteristics of many plants and
animals varied noticeably between the islands.
Hood Island- tortoises had long necks, curved shells
open around the legs, allowing the animal to get more access
to the sparse vegetation.
Isabella Island- tortoises had shorter necks, domed,
curved shell, allowing for the animals to feed better on the
more abundant vegetation that was close to the ground.
• Many specimens of finches were collected and differences
were observed in the shapes and sizes of their beaks.
• After returning to England, Darwin began to wonder if the
animals living on the islands were once members of the same
species.
Supporting Observations For
the Theory of Evolution
Geologic Records
• Earth has been estimated to be between 4.5-5 billion
years old. (Determined through radioactive carbon
dating).
• Fossil remains-the direct or indirect remains of
organisms preserved in media such as tar, ice, rock, or
amber.
• Fossils of prokaryotic life indicate that life existed
over 3.4 billion years ago.
• Fossils can be found in the upper, and lower strata.
These have been found to resemble each other,
suggesting a connection between modern forms and
older forms, as well as, divergent pathways from
common ancestors.
Comparative Anatomy
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Comparative studies of certain organisms indicate
similarities in anatomical features.
Homologous structures- anatomical parts that are similar
in structure and origin (development), but function
differently. (Ex.- wing of bird, arm of man, foreleg of
horse).
Homologous bones exist in the forelimbs of many
different vertebrates such as birds, horses, man, bats,
whales.
Analogous structures- are similar in appearance and
function, but have developmental differences. (Ex.- wing
of bird and wing of butterfly).
Homologies
Can be:
Molecular- share same biochemical coding, so
have identical genes and code for the same
amino acids
Developmental – share similar early
development events (embryology)
Comparative Embryology
The study of embryonic developments among groups
of organisms reveals similarities that suggest
common ancestry.
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Early vertebrate embryos resemble each other.
As development proceeds, the distinctive
features of each species becomes apparent.
All have gill slits, tail-bones (coccyx), segmented
backbones, and are C-shaped.
Comparative Cytology
According to the cell theory, the cell is the unifying
structure for living things. Organelles such as the
cell membrane, ribosomes, and mitochondria, are
structurally and functionally similar in most
divergent organisms. This suggests that all living
things are related to some degree. The fewer the
differences in these cell structures, the closer
the relationship appears.
Comparative Biochemistry
• Nucleic acids, their structure and
function, are similar in living
organisms.
• Many different organisms have
similar proteins and enzymes.
• In order for this similarity to
occur, their DNA must be similar.
• The greater their biochemical
similarity, the closer the
relationship among organisms,
thus suggesting evolutionary
relationships.
Vestigial Structures
• These are structures that do not have
any use, but are the remains of
structures that were once functional in
ancestral organisms.
• Some examples of vestigial organs are:
Humans- appendix, coccyx, 3rd molars
Horses- splint bones
Whales- pelvic (hip) bones
Modern Theory of Evolution
(continued)
A Time Frame for Evolution
Geographic Isolation
Geographic Isolation- favors speciation
by segregating a small group of
organisms from the main population.
Changes in gene frequency are more
likely to occur in a small population. In
time, this isolated population may
evolve into a separate species due to:
• Different initial gene frequencies than
the main population.
• Different mutations occur within the
main population and the isolated
population.
• Different environmental factors, thus
having different selection pressures
on each population
• An example of this would be Darwin’s
Finches, and Australia’s marsupials,
and the Albert Squirrel.
Reproductive
Isolation
Reproductive Isolation- separated groups my become
so divergent that even geographic barriers were
removed, interbreeding could not take place. Thus
the populations have become reproductively
isolated and are now two separate species.
• These populations now have separate gene pools.
• Reproductive Isolation results from various
isolating mechanisms that include: Geographic
Isolation, Behavioral Isolation, or Temporal
Isolation.
A Time Frame for Evolution
Gradualism- Gradualism proposes that
evolution is slow , gradual, and continuous.
This viewpoint is supported by geologic
fossils, which show slight changes in
organisms between adjacent layers of
sedimentary rocks.
• Species originate through gradual change
of adaptations. There is one line of
descent.
Time Frame (cont.)
Punctuated Equilibrium- Punctuated Equilibrium proposes that
species have long periods of stability, interrupted by
geologically brief periods of significant change, during which
a new species may evolve.
• This was proposed by Niles Eldredge, and Stephen Gould in
1972.
• Speciation occurs in relatively quickly, in rapid bursts,
followed by long periods of genetic stability in between.
• Environmental changes (higher temps., and introduction of
competitive species) lead to rapid changes in a small
population’s gene pool that is reproductively isolated from
the main population.
• Speciation happens relatively quickly- 10,000 years or less.
• Punctuated Equilibrium involves many lines of descent, it is
a pattern of long, stable periods, interrupted by brief
periods of more rapid change.