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1Descent with Modification A Darwinian View of
Life
CH 22
Historical Context for Evolutionary Theory
1.Western culture resisted evolutionary views of
life 2.Theories of geologic gradualism helped
clear the path for evolutionary
biologists 3.Lamarck placed fossils in an
evolutionary context
2Introduction
- On November 24, 1859,
Charles Darwin published
On the Origin of Species by
Means of Natural Selection. - Connecting what had once
seemed a bewildering array
of unrelated facts.
- Two main points in The Origin of Species
- Todays organisms descended from ancestral
species. - Natural selection provided a mechanism for
evolutionary change in populations.S
3Western culture resisted evolutionary views of
life
- The Origin of Species challenged a worldview that
had been accepted for centuries. - The key classical Greek philosophers who
influenced Western culture, Plato and Aristotle,
opposed any concept of evolution. - Plato believed in two worlds one real world that
is ideal and perfect and an illusory world of
imperfection that we perceive through our senses. - Aristotle believed that all living forms could be
arranged on a ladder (scala naturae) of
increasing complexity with every rung taken with
perfect, permanent species. Species are permanent
and do not change.
4- In the 1700s, the dominant philosophy, natural
theology, was dedicated to studying the
adaptations of organisms as evidence that the
Creator had designed each species for a purpose. - Carolus Linnaeus, a Swedish botanist, developed
taxonomy, a system for naming species and
grouping species into a hierarchy of increasingly
complex categories. - He believed that classification would reveal a
divine plan.
Carolus Linnaeus (1707-1778)
5- Darwins views were influenced by fossils, the
relics or impressions of organisms from the past,
mineralized in sedimentary rocks. - Sedimentary rocks form when mud and sand settle
to the bottom of seas, lakes, and marshes. - New layers of sediment cover older ones, creating
layers of rock called strata. - Fossils within layers show that a succession of
organisms have populated Earth throughout time.
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7Paleontology, the study of fossils, was largely
developed by Georges Cuvier, a French
anatomist. -realized that each stratum of earth
is characterized by different fossils.
- Cuvier recognized that extinction had been a
common occurrence in the history of life. - Instead of evolution, Cuvier advocated
catastrophism, that boundaries between strata
were due to local flood or drought that destroyed
the species then present. - Later, this area would be repopulated by species
immigrating from other unaffected areas. - Strongly opposed evolution.
8Theories of geologic gradualism helped clear the
path for evolutionary biologists
- In contrast to Cuviers catastrophism, James
Hutton, a Scottish geologist, proposed a theory
of gradualism in 1795. - Earth had been molded, not by sudden, violent
events, but slow, gradual change - Wind, water and weather formed the Earth.
- Proposed that the Earth was VERY old.
James Hutton
9- Later, Charles Lyell, a geologist, proposed a
theory of uniformitarianism.
- Geological processes had not changed throughout
Earths history. - Earth was very old!
Charles Lyell
Uniformitarianism is the assumption that the
natural processes operating in the past are the
same as those that can be observed operating in
the present
-contrast with catastrophism
10- Huttons and Lyells observations and theories
had a strong influence on Darwin. - First, if geologic changes result from slow,
continuous processes, rather than sudden events,
then the Earth must be far older than the 6,000
years assigned by theologians from biblical
inference. - Second, slow and subtle processes persisting for
long periods of time can add up to substantial
change.
11Lamarck placed fossils in an evolutionary context
- In 1809, Jean Baptiste Lamarck published a theory
of evolution based on his observations of fossil
invertebrates in the Natural History Museum of
Paris.
- Lamarck thought that he saw what appeared to be
several lines of descent in the collected fossils
and current species. - Each was a chronological series of older to
younger fossils leading to a modern species.
1809-Darwin was born
12- Central to Lamarcks mechanism of evolution were
the concepts of use and disuse of parts and of
inheritance of acquired characteristics. - Proposed that body parts used extensively to cope
with the environment became larger and stronger,
while those not used deteriorated. - These modifications acquired during the life of
an organism could be passed to offspring. - A classic example of these is the long neck of
the giraffe.
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14Inheritance of Acquired Characteristics
- Lamarcks theory was a visionary attempt to
explain both the fossil record and the current
diversity of life through its recognition of the
great age of Earth and adaptation of organisms to
the environment. - However, there is no evidence that acquired
characteristics can be inherited. - A lizard that didn't use it legs would eventually
not have legs and its offspring wouldn't have
legs - A giraffe stretched its neck to reach higher
leaves, and this stretched neck would be a trait
inherited by its offspring - Acquired traits (e.g., bigger biceps) do not
change the genes transmitted by gametes to
offspring.
15Alfred Russel Wallace -1858-emphasis was based on
the idea of competition for resources as the main
force in natural selection
- He independently proposed a theory of natural
selection which prompted Charles Darwin to
publish his own more developed and researched
theory sooner than he had intended. - Father of biogeography".
January 8, 1823 November 7, 1913
- Publications
- Wallace, Alfred Russel (2000 originally
published 1869). The Malay Archipelago.
Singapore Periplus Press. ISBN 962-593-645-9. - Wallace, Alfred Russel (1870). Contributions to
the Theory of Natural Selection. - Wallace, Alfred Russel (1876). The Geographical
Distribution of Animals. - Wallace, Alfred Russel (1898). Vaccination A
Delusion. Swan Sonnenschein Co.
16- Charles Darwin (1809-1882) was born in western
England. - While Darwin had a consuming interest in nature
as a boy, his father sent him to the University
of Edinburgh to study medicine. - Darwin left Edinburgh without a degree and
enrolled at Christ College at Cambridge
University with the intent of becoming a
clergyman. - At that time, most naturalists and scientists
belonged to the clergy and viewed the world in
the context of natural theology.
CLIP
Edinburgh
Cambridge
17- Darwin received his degree in 1831.
- After graduation Darwin was recommended to be the
conversation companion to Captain Robert FitzRoy,
who was preparing the survey ship HMS Beagle for
a voyage around the world. - FitzRoy chose Darwin because of his education,
and because he was of the same social class, and
was close in age to the captain.
18Field research helped Darwin frame his view of
life
- The main mission of the five-year voyage of the
Beagle was to chart poorly known stretches of the
South American coastline.
19Darwin had the freedom to explore extensively on
shore while the crew surveyed the coast.
- He collected thousands of specimens of the exotic
and diverse flora and fauna of South America. - Darwin explored the Brazilian jungles, the
grasslands of the Argentine pampas, the
desolation of Tiera del Fuego, and the heights of
the Andes.
20- Darwin noted that the plants and animals of South
America were very distinct from those of Europe. - Organisms from temperate regions of South America
were more similar to those from the tropics of
South America than to those from temperate
regions of Europe. - Further, South American fossils more closely
resembled modern species from that continent than
those from Europe.
21- The origin of the fauna of the Galapagos, 900 km
west of the South American coast, especially
puzzled Darwin. - Darwin noted that while most of the animal
species on the Galapagos lived nowhere else, they
resembled species living on the South American
mainland.
22- While on the Beagle, Darwin read Lyells
Principles of Geology. - Lyells ideas and his observations on the voyage
led Darwin to doubt the churchs position that
the Earth was static and only a few thousand
years old. - Instead, he was coming to the conclusion that the
Earth was very old and constantly changing.
23- After his return to Great Britain in 1836, Darwin
began to perceive that the origin of new species
and adaptation of species to the environment were
closely related processes. - For example, clear differences in the beak among
the 13 types of finches that Darwin collected in
the Galapagos are adaptations to the foods
available on their home islands.
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26- By the early 1840s Darwin had developed the major
features of his theory of natural selection as
the mechanism for evolution. - In 1844, he wrote a long essay on the origin of
species and natural selection, but he was
reluctant to publish his theory and continued to
compile evidence to support his theory. - In June 1858, Alfred Wallace, a young naturalist
working in the East Indies, sent Darwin a
manuscript containing a theory of natural
selection essentially identical to Darwins.
Alfred Wallace
27The Origin of Species developed two main points
- Evolution is the explanation for lifes unity and
diversity. - Natural selection is the cause of adaptive
evolution.
the occurrence of evolution and natural
selection as its mechanism
28Central to Darwins view of the evolution of life
is descent with modification
- All present day organisms are related through
descent from unknown ancestors in the past.
Descendents of these ancestors accumulated
diverse modifications or adaptations that fit
them to specific ways of life and
habitats.
29This evolutionary tree of the elephant family is
based on evidence from fossils.
Descent with modification
30The other major point that Darwin pioneered is a
unique mechanism of evolution - the theory of
natural selection.
- Darwins main ideas can be summarized as
follows. - Populations tend to grow exponentially,
overpopulate, and exceed their resources. - Overpopulation results in competition and
struggle for existence. - In any population, there is variation and an
unequal ability of individuals to survive and
reproduce. - Only the best-fit individuals survive and get to
pass on their traits to offspring. - Evolution occurs as advantageous traits
accumulate in a population.
31For example, related species of insects called
mantids have diverse shapes and colors that
evolved in different environments.
32- In each generation, environmental factors
filter heritable variations, favoring some
over others. - Differential reproduction -- whereby organisms
with traits favored by the environment produce
more offspring than do organisms without those
traits -- results in the favored traits being
disproportionately represented in the next
generation. - This increasing frequency of the favored traits
in a population is evolution.
33Peppered Moth
- Two versions of the moth-
- Black and peppered
- During the industrial revolution on England
- Population of moths changed
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35- Darwins views on the role of environmental
factors in the screening of heritable variation
were heavily influenced by artificial selection. - Humans have modified a variety of domesticated
plants and animals over many generations by
selecting individuals with the desired traits as
breeding stock.
36Natural selection can only amplify or diminish
heritable variations, not variations that an
individual acquires during its life, even if
these variations are adaptive.
37- In general, natural selection operates not to
create variation, but to edit existing variation. - For example, resistant insects are favored and
non-resistant individuals are not when
insecticides are applied. - Natural selection favors those characteristics in
a variable population that fit the current, local
environment.
38Other evidence of evolution
39Rock layer
40Isotope dating-radioactive dating
- Half-life
- 14C
- Earth
- 4.6 billion years old
41Comparative Anatomy
42Homologous structures
Reflect common ancestry
- Anatomical similarities between different
species. - Ex forelimbs of human, cats, whales, and bats
share the same skeletal elements, but different
functions because they
diverged from their
common
ancestor.
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44Analogous structures
- Bats wing and a flys wing have the same
function However they have different ancestors. - They have simply adapted to similar environments.
- Convergent evolution
45- While the sugar glider and flying squirrel have
adapted to the same mode of life, they are not
closely related. - Instead, the sugar glider from Australia is more
closely related to other marsupial mammals from
Australia than to the flying
squirrel, a placental
mammal from North America. - The resemblancebetween them is
another example
ofconvergentevolution.
Analogous structures
46Vestigial structures
- Structures that have marginal, if any, importance
to a current organism, but which had important
functions in ancestors.
They are usually reduced in size
47Vestigial structures
48Comparative Embryology
- Similar stages in embryonic development.
- Ex All vertebrates embryos go through a stage in
which they have gill pouches on the sides of the
throats. - Fish-gills
- Humans-eustachian . tubes
49Comparative Embryology
- Sometimes, homologies that are not obvious in
adult organisms become evident when we look at
embryonic development. - For example, all vertebrate embryos have
structures called pharyngeal pouches in their
throat at some stage in their development. - These embryonic structures develop into very
different, but still homologous, adult
structures, such as the - gills of fish or
- the Eustacean tubes that connect the middle ear
with the throat in mammals.
50Molecular Biology
51Molecular Biology
- Molecular biology allows links between organisms
that have no macroscopic anatomy in common - All species of life have the same basic genetic
machinery of RNA and DNA and the genetic code is
essentially universal. - -The language of the genetic code has been passed
along through all the branches of the tree of
life ever since the codes inception in an early
life-form. - All aerobic organism contain the polypeptide
cytochrome C - -Amino acids sequence of CytoC can show how
closely related two species are.
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54The geographical distribution of species --
biogeography -- first suggested evolution to
Darwin.
55Theory of Continental drift 200mya-Pangaea Today-
7 continents Wagner
56- Species tend to be more closely related to other
species from the same area than to other species
with the same way of life, but living in
different areas. - For example, even though some marsupial mammals
(those that complete their development in an
external pouch) of Australia have look-alikes
among the eutherian mammals (those that complete
their development in the uterus) that live on
other continents, all the marsupial mammals are
still more closely related to each other than
they are to any eutherian mammal.
eutherian mammals
57Distribution of Living Species
Beaver
Beaver Muskrat Beaver andMuskrat Coypu
Capybara Coypu andCapybara
NORTH AMERICA
Muskrat
Capybara
SOUTH AMERICA
Coypu
58- Island and island archipelagos have provided
strong evidence of evolution. - Often islands have many species of plants and
animals that are endemic, or found nowhere else
in the world. - As Darwin observed when he reassessed his
collections from the Beagles voyage, these
endemic species are typically related more
closely to species living on the nearest mainland
(despite different environments) than those from
other island groups.
59- All of the 500 or so endemic species of
Drosophila in the Hawaiian archipelago descended
from a common ancestor that reached Kauai over 5
million years ago.
60All of that being said, be aware that..
- Natural selection is widely accepted in science
because its predictions have withstood thorough,
continual testing by experiments and
observations. - However, science is not static and arguments
exist among evolutionary biologists concerning
whether natural selection alone accounts for the
history of life as observed in the fossil record. - The study of evolution is livelier than ever, but
these questions of how life evolves in no way
imply that most biologists consider evolution
itself to be just a theory.
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62Timeline
63BC Aristotle Species are permanent, arranged on a ladder.
1700s Carolus Linnaeus Taxonomy, classification shows relationships, classification would reveal a divine plan
1700s Georges Cuvier Studied fossils, opposed evolution, catastrophes responsible for changes in organisms
1795 James Hutton Gradualism, Earth molded by weather, Earth has a long history
1798 Thomas Malthus Populations outgrow their food supplies, causing competition
1809 Jean Baptiste Lamarck Inheritance of acquired characteristics.
1833 Charles Lyell Geologist, Earth more than 6,000 years old, Principles of Geology, uniformitarianism
1858 Alfred Russel Wallace Proposed natural selection as the mechanism for evolution
1859 Charles Darwin Theory of Natural Selection, On the Origin of the Species by Natural Selection