Evolution

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Evolution
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Wooly mammotn skeleton Mammoths lived 2 million
to about 9,000 years ago. They were about 9 to
15 feet tall. What was the reason for the
extinction?
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What is Evolution?

• Evolution involves inheritable changes in
  organisms through time
• Fundamental to biology and paleontology
• Paleontology is the study of life history as
  revealed by fossils
• Explains the development of life

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First, Lets Define Life

• The definition must be built on descriptions
  that fit all living things.
• Living things are both complex and organized
• Living things grow and reproduce
• Living things respond to stimuli
• Living things acquire and use materials and
  energy
• Living things have (use) DNA to store information

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Misconceptions of evolution

• Evolution proceeds strictly by chance
• Nothing less than fully developed structures,
  such as eyes, are of any use
• There are no transitional fossils
• so-called missing links connecting ancestors and
  descendants
• Evolved species must be more complex than the
  predecessor
• humans evolved from monkeys so monkeys should no
  longer exist

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Historical Perspective

• Evolution is usually attributed solely to Charles
  Darwin, but actually considered long before he
  was born.
• By some ancient Greeks and by philosophers and
  theologians during the Middle Ages
• Nevertheless, the prevailing belief in the 1700s
  was that the Bibles book of Genesis explained
  the origin of life.

Contrary views were heresy!
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Historical Perspective

• During the 18th century, naturalists were
  discovering evidence that could not be reconciled
  with literal interpretation of Scripture
• Scientists gradually accepted a number of ideas
• The principle of uniformitarianism,
• Earths great age
• Many types of plants and animals had become
  extinct
• change from one species to another occurred
• Species existed on Earth that were no longer
  living (extinct)
• What was lacking, though, was a theoretical
  framework to explain evolution

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Evolution

• A theory explains a series of observations and
  often unifies related facts through supportive
  evidence.
• Evolution is based on the observed accumulated
  generation to generation changes within a defined
  group.
• Evolution accounts for both
• Lifes unity similarities among life forms
• Lifes diversity differences among life forms

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Lamark

• Jean-Baptiste de Lamarck
• (1744-1829) is best remembered for his theory of
  Inheritance of Acquired Characteristics.
• According to this theory
• new traits arise in organisms because of their
  needs
• Once acquired new traits are somehow passed on to
  their descendants
• Lamarcks theory seemed logical at the time and
  was widely accepted

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Lamarks Theory
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Darwin

• In 1859, Charles Robert Darwin (1809-1882)
  published
• On the Origin of Species
• In it he detailed his ideas on evolution
  formulated 20 years earlier and proposed a
  mechanism for evolution

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Darwin is most associated with his time at
the Galapagos Islands (only 5 weeks!). Here he
Observed distinct differences among
similaranimals that were directly related to
foodsupply. He published his ideas 24 yrs.
later.
Fig. 7-1, p. 115
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What he noticed

• Plant and animal breeders practice artificial
  selection
• by selecting desirable traits and then breeding
  plants and animals with those traits
• Observing artificial selection gave Darwin the
  idea that a process of selection among variant
  types in nature could also bring about change
• Thomas Malthuss essay on population suggested
  that competition for resources and high infant
  mortality limited population size

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Natural Selection (Key Points)

• Organisms in all populations posses heritable
  variations.
• size, speed, agility, visual acuity, digestive
  enzymes, color, and so forth
• Some variations are more favorable than others
• some have a competitive edge in acquiring
  resources and/or avoiding predators
• Not all young survive to reproductive maturity
• However, Those with favorable variations are more
  likely to survive and pass on their favorable
  variations

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Back to the Giraffeswhy would giraffes
develop or actually express the trait longer
necks over time?
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Survival of the Fittest

• In colloquial usage, natural selection is
  sometimes expressed as survival of the fittest
• This is misleading because natural selection is
  not simply a matter of survival but involves
  differential rates of survival and reproduction

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What does Survival of the Fittest actually mean
over time??

• Misconception
• among animals only the biggest, strongest, and
  fastest are likely to survive
• These characteristics might provide an advantage
  but natural selection may favor species other
  than the obviously bigger, stronger, or faster.
  Examples?
• the smallest if resources are limited
• the most easily concealed
• those that adapt most readily to a new food
  source
• those having the ability to detoxify some
  substance
• Others?

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The Cretaceous Tertiary Boundary also known
today as the Cretaceous Paleogene BoundaryWhat
life forms were lost, and which survived?

• Photosynthesizing organisms, including
  phytoplankton and land plants, formed the
  foundation of the food chain in the late
  Cretaceous as they do today. Evidence suggests
  that herbivorous animals died out when the plants
  they depended on for food became scarce
  consequently, top of the food chain predators
  such as Tyrannosaurus rex also perished.
• Coccolithophorids and molluscs, including
  ammonites, rudists, freshwater snails and
  mussels, and those organisms whose food chain
  included these shell builders, became extinct or
  suffered heavy losses. For example, it is thought
  that ammonites were the principal food of
  mosasaurs, a group of giant marine reptiles that
  became extinct at the boundary.
• Omnivores, insectivores and carrion-eaters
  survived the extinction event, perhaps because of
  the increased availability of their food sources.
  At the end of the Cretaceous there seem to have
  been no purely herbivorous or carnivorous
  mammals. Mammals and birds that survived the
  extinction fed on insects, worms, and snails,
  which fed on dead plant and animal matter.
  Scientists hypothesize that these organisms
  survived the collapse of plant-based food chains
  because they fed on detritus

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So, is natural selection the mechanism for
evolution?

• Observers knew that life on earth has changed
  with time.
• Some explanations were plausible, such as the
  extinction or inability for an organism to
  survive.
• Other observations were not as easy to
  explain, and more scientific investigation and
  application was needed to support the hypotheses.

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Limits on Natural Selection

• Natural selection works on existing variation in
  a population
• It could not account for the origin of variations
• Critics reasoned that should a variant trait
  arise, it would blend with other traits and would
  be lost
• The answer to these criticisms existed even then
  in the work of Gregor Mendel, but remained
  obscure until 1900

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Gregor Mendel

• During the 1860s, Gregor Mendel, performed a
  series of controlled experiments with
  true-breeding strains of garden peas
• strains that when self-fertilized always display
  the same trait, such as flower color
• Traits are controlled by a pair of factors now
  called genes
• Genes occur in alternate forms, called alleles
• One allele may be dominant over another
• Offspring receive one allele of each pair from
  each parent

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Mendels Work

• The parental generation consisted of
  true-breeding strains
• RR red flowers
• rr white flowers
• Cross-fertilization yielded a second generation
• all with the Rr combination of alleles, in which
  the R (red) is dominant over r (white)

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Mendels Work

• The second generation, when self-fertilized
  produced a third generation with a ratio of three
  red-flowered plants to one white-flowered plant

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Why is this important?

• The factors (genes) controlling traits do not
  blend during inheritance
• Traits not expressed in each generation may not
  be lost
• Therefore, some variation in populations results
  from alternate expressions of genes (alleles)
• Variation can be maintained!
• Why is variation important to survival of a
  species?
• To be continued! Read Chapter 7

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Modern Genetics
Complex, double-stranded helical molecules of
deoxyribonucleic acid (DNA) called chromosomes
are found in cells of all organisms except
bacteria which have ribonucleic acid
(RNA) Specific segments of DNA are the basic
units of heredity (genes) The number of
chromosomes varies from one species to
another fruit flies 8 humans 46 horses 64
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Modern Thinking

• During the 1930s and 1940s,
• paleontologists, population biologists,
  geneticists, and others developed ideas that
  merged to form a modern synthesis or
  neo-Darwinian view of evolution
• They incorporated chromosome theory of
  inheritance into evolutionary thinking
• They saw changes in genes (mutations) as only one
  source of variation

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Most Importantly

• They completely rejected Lamarcks idea of
  inheritance of acquired characteristics
• They reaffirmed the importance of natural
  selection
• But since then, some scientists have challenged
  the emphasis in modern synthesis that evolution
  is gradual

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Remember

• Evolution by natural selection works on variation
  in populations
• most of which is accounted for by the reshuffling
  of alleles from generation to generation during
  sexual reproduction
• The potential for variation is enormous with
  thousands of genes each with several alleles, and
  with offspring receiving 1/2 of their genes from
  each parent
• New variations arise by mutations
• change in the chromosomes or genes

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Mutations

• Mutations result in a change in hereditary
  information
• ONLY mutations that take place in sex cells are
  inheritable,
• Can be chromosomal mutations (affecting a large
  segment of a chromosome)
• or point mutations (individual changes in
  particular genes)
• Mutations are random with respect to fitness
• they may be beneficial, neutral, or harmful to
  survival!

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Mutations

• If a species is well adapted to its environment,
  most mutations would not be particularly useful
  and perhaps could be harmful
• But what was once a harmful mutation can become a
  useful one if the environment changes

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The Species

• Species is a biological term for a population of
  similar individuals that in nature interbreed and
  produce fertile offspring
• Species are reproductively isolated from one
  another
• Goats and sheep do not interbreed in nature, so
  they are separate species
• When artifically bred in captivity, offspring are
  most often sterile.

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Recipe for a species

• Speciation is the process by which a new species
  arises from an ancestral species
• It involves change in the genetic makeup of a
  population,
• which also may bring about changes
• in form and structure
• During allopatric speciation,
• species arise when a small part of a population
  becomes isolated from its parent population

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Variations among Darwins finches were
naturally selected from among the existing
variations within the gene pool and mutations
that may have occurred. What would cause the
selection of the observed variations?
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Allopatric Speciation

• Reduction of the area occupied by a species may
  leave a small isolated population
• Two peripheral isolates evolved into new species
  (i.e. Darwins finches)

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Hmmmbut how long does it take for changes to
appear?

• Although widespread agreement exists on
  allopatric speciation scientists disagree on how
  rapidly a new species might evolve
• Phyletic gradualism- the gradual accumulation of
  minor changes which eventually bring about new
  species

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Punctuated Equilibrium
holds that little or no change takes place in a
species during most of its existence then
evolution occurs rapidly
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Misconceptions

• One antievolution argument is If humans evolved
  from monkeys, why are there still monkeys?
• This involves two misconceptions
• No scientist has ever claimed that humans evolved
  from monkeys
• Even if they had, that would not preclude
• the possibility of monkeys still existing

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Styles of Evolution

• Divergent evolution occurs when an ancestral
  species giving rise to diverse descendants adapts
  to various aspects of the environment
• Divergent evolution leads to descendants that
  differ markedly from their ancestors
• Convergent evolution involves the development of
  similar characteristics in distantly related
  organisms
• Parallel evolution involves the development of
  similar characteristics in closely related
  organisms

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Divergent Evolution
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Convergent Evolution
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Parallel Evolution
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Evolutionary Novelties

• All land-dwelling vertebrate animals posses bone
  and paired limbs so these characteristics are
  primitive and of little use in establishing
  relationships among land vertebrates
• However, hair and mammary glands are derived
  characteristics.
• Only one subclade, the mammals, has them

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It wouldnt be Geology without Death and
Destruction..

• Perhaps as many as 99 of all species that ever
• existed are now extinct
• Organisms do not always evolve toward some kind
  of higher order of perfection or greater
  complexity
• Vertebrates are more complex but not necessarily
  superior in some survival sense than bacteria
• after all, bacteria have persisted for at least
  3.5 billion years
• Natural selection yields organisms adapted to a
  specific set of circumstances at a particular time

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Extinction

• The continual extinction of species is referred
  to as background extinction
• It is clearly different from mass extinction
  during which accelerated extinction rates sharply
  reduce Earths biotic diversity
• Extinction is a continual occurrence
• so is the evolution of new species that usually
  quickly exploits the opportunities another
  species extinction creates
• Mammals began a remarkable diversification when
  they began occupying niches the extinction of
  dinosaurs and their relatives left vacant

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Extinction

• The mass extinction of dinosaurs and other
  animals at the end of Mesozoic Era is well
  knownbut not the greatest loss of biologic
  diversity!
• The greatest mass extinction occurred at the end
  of the Paleozoic Era end of Permian
• More than 90 of all species died out
• We will discuss these extinctions and their
  possible causes throughout the rest of the term

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