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Descent 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
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Introduction

• 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

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Western 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.

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• 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)
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• 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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Paleontology, 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.

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Theories 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
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• 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
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• 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.

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Lamarck 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
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• 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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Inheritance 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.

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Alfred 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.

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• 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
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• 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.

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Field 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.

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Darwin 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.

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• 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.

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• 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.

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• 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.

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• 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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• 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
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The Origin of Species developed two main points

1. Evolution is the explanation for lifes unity and
   diversity.
2. Natural selection is the cause of adaptive
   evolution.

the occurrence of evolution and natural
selection as its mechanism
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Central 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.
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This evolutionary tree of the elephant family is
based on evidence from fossils.
Descent with modification
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The 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.

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For example, related species of insects called
mantids have diverse shapes and colors that
evolved in different environments.
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• 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.

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Peppered Moth

• Two versions of the moth-
• Black and peppered
• During the industrial revolution on England
• Population of moths changed

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• 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.

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Natural selection can only amplify or diminish
heritable variations, not variations that an
individual acquires during its life, even if
these variations are adaptive.
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• 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.

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Other evidence of evolution

• Fossil record

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Rock layer
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Isotope dating-radioactive dating

• Half-life
• 14C
• Earth
• 4.6 billion years old

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Comparative Anatomy
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Homologous 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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Analogous 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

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• 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
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Vestigial 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
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Vestigial structures

• Whale pelvis

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Comparative 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

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Comparative 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.

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Molecular Biology
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Molecular 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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The geographical distribution of species --
biogeography -- first suggested evolution to
Darwin.
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Theory of Continental drift 200mya-Pangaea Today-
7 continents Wagner
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• 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
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Distribution of Living Species
Beaver
Beaver Muskrat Beaver andMuskrat Coypu
Capybara Coypu andCapybara
NORTH AMERICA
Muskrat
Capybara
SOUTH AMERICA
Coypu
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• 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.

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• 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.

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All 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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Timeline
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BC 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