Evolution

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Evolution

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Title: Evolution


1
Evolution
2
What is a theory?
  • A widely accepted explanatory idea that is broad
    in scope and supported by a large body of
    evidence.
  • http//www.pbs.org/wgbh/evolution/library/11/2/e_s
    _1.html

3
What is evolution?
  • History of defining evolution
  • About 2,500 years ago, the Greek philosopher
    Anaximander
  • promoted the idea that life arose in water and
    that simpler forms of life preceded more complex
    ones.
  • The Greek philosopher Aristotle
  • generally held that species are fixed, or
    permanent, and do not evolve.
  • Judeo-Christian culture
  • fortified this idea with a literal interpretation
    of the Book of Genesis, holding that all species
    were individually designed by a divine creator.
  • The idea that all living species are static in
    form and inhabit an Earth that is most about
    6,000 years old dominated the intellectual and
    cultural climate of the Western world for
    centuries.

4
What is evolution?
  • History of defining evolution
  • Carl Linneaus (18th century)
  • The father of taxonomy.
  • Used binomial nomenclature, came up with the
    hierarchical classification theme, used visible
    characteristics to classify plants and animals.
  • Thomas Malthus (18th 19th century)
  • Attempedto justify the conditions of the poor by
    stating that poverty and starvation were merely a
    consequence of overpopulation.

5
What is evolution?
  • History of defining evolution
  • Lamarck (18th 19th century)
  • First to publish a reasoned theory of evolution
    A) the idea of use and disuse B) inheritance of
    acquired characteristics
  • Lyell (19th century)
  • natural processes form geological formations over
    a long period of time, erosion and other forces
    that shape rocks are very slow processes that
    take millions of years, so the earth must be
    older than previously believed.
  • Wallas (19th 20th century)
  • theory of evolution by natural selection.

6
What is evolution?
  • History of evolution (continued)
  • In the early 1800s, French naturalist Jean
    Baptiste Lamarck suggested that the best
    explanation for this relationship of fossils to
    current organisms is that life evolves.
  • Today, we remember Lamarck mainly for his
    erroneous view of how species evolve.
  • He proposed that by using or not using its body
    parts, an individual may develop certain traits
    that it passes on to its offspring.
  • Larmarcks idea is known as the inheritance of
    acquired characteristics.
  • He suggested, for instance, that the ancestors of
    the giraffe had lengthened their necks by
    stretching higher and higher into the trees to
    reach leaves.
  • Although his ideas were incorrect, he helped to
    set the stage for Darwin by strongly advocating
    evolution and by proposing that species evolve as
    a result of interactions with their environment.

7
What is evolution?
Charles Darwin
8
What is evolution?
  • Charles Darwin
  • Born in 1809, the same year that Lamarck
    published some of his ideas on evolution.
  • In December 1831, at the age of 22, Darwin began
    a round-the-world sea voyage that profoundly
    influenced his thinking and eventually the
    thinking of the entire world.
  • He accompanied the captain of the HMS Beagle, a
    surveying ship, on a mission to chart poorly
    known stretches of the South American coastline.
  • Darwin actually spent most of his time onshore,
    collecting thousands of specimens of fossils and
    living plants and animals.
  • He noted the unique adaptations of these South
    American organisms in places as different as the
    Brazilian jungle, the grasslands of the pampas,
    and the frigid Anarctica.
  • He asked himself why fossils of the South
    American continent were more similar to modern
    South American species than to fossils of other
    continents.

9
What is evolution?
  • Charles Darwin (continued)
  • Other questions arose from Darwins visit to the
    Galapagos Islands.
  • Darwin observed that these islands had many
    unique organisms, most of which were similar to,
    but different from, the plants and animals of the
    nearest mainland.
  • Even the individual islands had some species that
    differed from those on other islands.
  • Referring to the islands and their unique
    inhabitants, he later wrote, Both in space and
    time, we seem to be brought somewhat near to that
    great factthat mystery of mysteriesthe first
    appearance of new beings on the earth.

10
What is evolution?
  • Charles Darwin (continued)
  • While on the voyage, Darwin read and was strongly
    influenced by the recently published Principles
    of Geology, by Scottish geologist Charles Lyell.
  • Lyells work led Darwin to realize that natural
    forces gradually change Earths surface and that
    these forces are still operating in modern times.
  • Darwin had collected fossils of marine snails in
    the Andes. Having read Lyells book and witnessed
    an earthquake that raised part of the coastline
    of Chile almost a meter, he came to believe that
    slow, natural processes such as the growth of
    mountains as a result of earthquakes, could
    account for the presence of marine snails on
    mountaintops.

11
What is evolution?
  • Charles Darwin (continued)
  • Upon Darwins return to Great Britain after his
    voyage, his experiences and reading had led him
    to doubt seriously that Earth and living
    organisms were unchangeable and had been
    specially created only a few thousand years
    earlier.
  • He analyzed his collections, discussed them with
    colleagues, continued to read, and maintained
    extensive journals of his observations, studies,
    and thoughts.
  • By the early 1840s, he had composed a long essay
    describing the major features of his theory of
    evolution. He realized that his ideas would cause
    a social furor, however, and he delayed
    publishing his essay.
  • In the mid 1850s, Wallace conceived a theory
    almost identical to Darwins. He asked Darwin to
    evaluate the manuscript he had written about his
    theory to see if it merited publication.
  • In 1858, two of Darwins colleagues presented
    Wallaces paper and excerpts of Darwins earlier
    essay together to the scientific community.

12
What is evolution?
  • Charles Darwin (continued)
  • He published his book On the Origin of Species by
    Means of Natural Selection in 1859.
  • He presented the world with an avalanche of
    evidence and a strong, logical argument for
    evolution. He also described his theory of
    natural selection, an explanation of how
    evolution occurs.
  • In the first edition of his book, Darwin did not
    actually use the word evolved until the very end,
    referring instead to descent with modification.
  • This phrase summarized Darwins view of life he
    perceived a unity among species, with all
    organism related through descent from an ancestor
    that lived in the remote past.
  • As the descendants of that ancestor spread into
    various habitats over millions of years, they
    accumulated diverse modifications, or
    adaptations, that accommodated them to diverse
    ways of life.
  • The history of life seemed to resemble a tree,
    with multiple branchings from a common trunk to
    the tips of the twigs.
  • At each fork of the evolutionary tree is an
    ancestor common to all lines of descent branching
    from that fork.
  • Species that are closely related share many
    characteristics because their lineage of common
    descent extends to the smallest branches of the
    tree of life.

13
Natural Selection
  • Darwins Theory of Evolution is based on several
    key observations and inferences
  • 1. Overproduction of offspring
  • Populations produce too many offspring, many must
    die.
  • 2. Struggle for existence
  • Food, water, and other resources are limited
    organisms compete with one another for these
    resources
  • 3. Variation
  • Individuals exhibit variation in a population and
    have a unique set of traits, and these traits get
    passed on from one generation to the next.
  • Some of these traits will improve their chance
    for survival while others are less favorable.
  • 4. Differential reproduction
  • Within a varied population, individuals whose
    characteristics adapt them best to their
    environment are most likely to survive and
    reproduce these individuals thus tend to leave
    more offspring than less fit individuals do.
  • Reproduction is central to what Darwin saw as the
    basic mechanism of evolution, the process he
    called natural selection.
  • Means by which the environment filters
    variations, favoring some over others.
  • Allows for a gradual change in characteristics of
    a population of organisms overtime

14
Artificial Selection
  • Darwin found convincing evidence for his ideas in
    the results of artificial selection, the
    selective breeding of domesticated plants and
    animals.
  • He saw that by selecting individuals with the
    desired traits as breeding stock, humans were
    playing the role of the environment and bringing
    about differential reproduction.
  • They were, in fact, modifying species.
  • Darwin reasoned that if so much change could be
    achieved in a relatively short period of time by
    artificial selection, then over hundreds or
    thousands of generations natural selection should
    be able to modify species considerably.
  • Such changes could account for the evolution of
    new species.

15
Evidence of Evolution
  • Darwin developed his theory of descent with
    modification mainly with evidence from the
    geographic distribution of species, examples of
    artificial selection, and the fossil record.
  • His careful documentation convinced many of the
    scientists of his day that organisms do indeed
    evolve.
  • 1. Fossil record
  • 2. Biogeography
  • 3. Comparative anatomy
  • 4. Comparative embryology
  • 5. Molecular biology

16
Evidence of Evolution
  • 1. Fossil record
  • Fossils document some of the drastic changes that
    life has undergone over time.
  • The organic substances of a dead organism usually
    decay rapidly, but hard parts of an animal that
    are rich in minerals, such as the bones and teeth
    of dinosaurs and the shells of clams and snails,
    may remain as fossils.
  • The fossil recordthe ordered array in which
    fossils appear within layers of sedimentary
    rockprovides some of the strongest evidence of
    evolution.
  • Sedimentary rocks form from layers (strata) of
    sand and mud that settle to the bottom of seas,
    lakes, and marshes.
  • Younger strata are on top of older ones thus,
    the relative ages of fossils can be determined by
    the layers in which they are found.
  • Fossil record shows that the oldest known
    fossils, dating from 3.5 billion years ago, are
    prokaryotes.
  • Fossils in younger layers reveal the evolution of
    various groups of eukaryotic organisms.

17
Evidence of Evolution
http//www.pbs.org/wgbh/evolution/library/03/3/l_0
33_01.html
18
Evidence of Evolution
  • 2. Biogeography
  • It was the geographic distributing of species,
    known as biogeography, that first suggested to
    Darwin that organisms evolve from common
    ancestors.
  • Darwin noted that Galapagos animals resembled
    species of the South American mainland more than
    they resembled animals on similar but distant
    islands.
  • The logical explanation was that the Galapagos
    species evolved from South American immigrants.
  • http//www.ucmp.berkeley.edu/geology/anim1.html

19
Evidence of Evolution
  • 3. Comparative Anatomy
  • The comparison of body structures in different
    species.
  • Anatomical similarities between many species give
    signs of common descent.
  • Similarity in characteristics that results from
    common ancestry is known as homology.
  • Homologous structures are features that often
    have different functions but are structurally
    similar because of common ancestry.
  • For example, the same skeletal elements make up
    the forelimbs of humans, cats, whales, and bats,
    all of which are mammals. However, the functions
    of these forelimbs differ.
  • The logical explanation is that the arms,
    forelegs, flippers, and wings of different
    mammals are variations on a common anatomical
    plan that has become adapted to different
    functions.

20
Evidence of Evolution
21
Evidence of Evolution
  • 3. Comparative Anatomy (continued)
  • Some of the most interesting homologous
    structures are vestigial organs, structures of
    marginal, if any, importance to the organism.
  • Remnants of structures that served important
    functions in the organisms ancestors.
  • For example, the small hind-leg and foot bones of
    modern whales, the skeletons of some snakes
    retain vestiges of the pelvis and leg bones of
    walking ancestors.

22
Evidence of Evolution
  • 4. Comparative Embryology
  • The comparison of early stages of development,
    called comparative embryology, is another major
    source of evidence fro the common descent of
    organisms.
  • One sign that vertebrates evolved from a common
    ancestor is that all of them have structures on
    the sides of the throat called pharyngeal
    (throat) pouches.
  • At this stage, the embryos of fishes, frogs,
    snakes, birds, and mammals look relatively alike.
  • They take on more and more distinctive features
    as development progresses.
  • For example, pharyngeal pouches develop into
    gills in fishes, but into parts of the ears and
    throats in humans.

23
Evidence of Evolution
24
Evidence of Evolution
  • 5. Molecular Biology
  • Recent advances in molecular biology have enabled
    biologists to read a molecular history of
    evolution in the DNA sequences of organisms.
  • If two species have genes with sequences that
    match closely, biologists conclude that these
    sequences must have been inherited from a
    relatively recent common ancestor.
  • In contrast, the greater the number of sequence
    differences between species, the less likely they
    share a close common ancestor.
  • Molecular comparisons between diverse organisms
    have allowed biologists to develop hypotheses
    about the evolutionary divergence of major
    branches on the tree of life.
  • Studies of the amino acid sequences of similar
    (homologous) proteins in different species have
    been a rich source of data about evolutionary
    relationships.
  • By comparing the amino acid sequence of
    hemoglobin, the following hypothesis was made
    about evolutionary relationships Rhesus monkeys
    are much more closely related to humans that are
    lampreys mice, chickens, and frogs fall in
    between.
  • This hypothesis agrees with conclusions from
    comparative anatomy and embryology, along with
    fossil evidence.

25
Evidence of Evolution
  • 5. Molecular Biology (continued)
  • There is also evidence showing that most (if not
    all) multicellular eukaryotes have similar genes
    regulating their early development.
  • The logical explanation is that these genes first
    arose in a common ancestor.
  • Darwins boldest hypothesis is that all
    life-forms are related.
  • Molecular biology has provided strong evidence
    for it All forms of life use DNA and RNA, and
    the genetic code is essentially universal.
  • This genetic language has been passed along
    through all the branches of evolution ever since
    its beginnings in an early form of life.
  • http//www.pbs.org/wgbh/evolution/library/03/4/l_0
    34_04.html

26
Natural Selection in Action
  • Many cases of natural selection in nature have
    been documented.
  • A classic example involves finches in the
    Galapagos Islands over a period of 20 years.
  • The research of scientists showed measurable
    changes in in beak size in a population of ground
    finches.
  • In dry years, when small seed are in short
    supply, birds must eat more large seeds. Birds
    with larger, stronger beaks have a feeding
    advantage and greater reproductive success, and
    the average beak depth for the population
    increases.
  • During wet years, smaller beaks are more
    efficient for eating the now abundant small
    seeds, and the average beak depth decreases.

27
Natural Selection in Action
28
Natural Selection in Action
  • Evolution in pesticide resistance in hundreds of
    insect species.
  • Pesticides are poisons used to kill insect pests
    in farmlands, swamps, backyards, and homes.
  • Whenever a new type of pesticide is used to
    control agricultural pests, a relatively small
    amount of poison dusted onto a crop may kill 99
    of the insects, but subsequent sprayings are less
    and less effective.
  • The few survivors of the first pesticide wave are
    insects with genes that somehow enabled them to
    resist chemical attack. So, the poison kills most
    members of the population, leaving the resistant
    individuals to reproduce and pass the genes for
    pesticide resistance to their offspring.
  • The proportion of pesticide-resistant individuals
    increases in each generation.
  • Like the finches, the insect population has
    adapted to environmental change through natural
    selection.

29
Natural Selection in Action
  • Antibiotics Resistance
  • Antibiotics are drugs that disable or kill
    infectious microorganisms.
  • Most antibiotics are naturally occurring
    chemicals derived from other microorganisms.
  • Pencillin, for example, was originally isolated
    from a mold and has been widely prescribed since
    the 1940s. A revolution in human healthy rapidly
    followed its introduction, rendering many
    previously fatal diseases easily curable (such as
    strep throat and surgical infections).
  • During the 1950s, some doctors even predicted the
    end of human infectious disease. Unfortunately,
    evolution destroys the optimism of this
    prediction.
  • In the same way that pesticides select for
    resistant insects, antibiotics select for
    resistant bacteria.
  • The genes that confer such antibiotic resistance
    are often carried on R plasmids, which are passed
    on to bacterial offspring and may even be
    transferred to other bacteria.
  • For nearly every antibiotic that has been
    developed, a resistant strain of bacterium has
    appeared within a few decades.
  • For example, some strains of the
    tuberculosis-causing bacterium are now resistant
    to all three of the antibiotics commonly used to
    treat the disease.

30
Natural Selection in Action
  • Antibiotics Resistance (continued)
  • In some ways, we are contributing to the problem
    of antibiotic resistance
  • Livestock producers add antibiotics to animal
    feed as a growth promoter.
  • As a result, much of the packaged meat for sale
    in supermarkets contains bacteria that are
    resistant to standard antibiotics.
  • Doctors contribute to the problem by
    overprescribing antibiotics, for example, to
    patients with viral infections, which do not
    respond to antibiotic treatment.
  • And patients contribute to this problem through
    misuse of prescribed antibioticsfor example, by
    prematurely stopping the medication before they
    feel better. This allows mutant bacteria that may
    be killed more slowly by the drug to survive and
    multiply. Subsequent mutations in such bacteria
    may lead to full-blown antibiotic resitance.
  • During the anthrax crisis of 2001, public health
    officials urged panicked citizens to avoid
    unnecessarily taking ciprofloxacin (Cipro), the
    drug used to treat the deadliest form of anthrax,
    because doing so could select for resistant
    bacteria.

31
Genetic Variation- Where does it come from?
  • Individual variation occurs in populations of all
    species that reproduce sexually.
  • Fresh assortments of existing alleles arise every
    generation from three random components of sexual
    recombination crossing over, independent
    assortment of homologous chromosomes, and random
    fertilization.
  • Mutation is the ultimate source of the genetic
    variation that serves as raw material for
    evolution.
  • Mutations are changes in the nucleotide sequence
    of DNA that can create new alleles.
  • Most mutations occur in body cells and are lost
    when the individual dies.
  • Only mutations in cells that produce gametes can
    be passed to offspring and potentially affect a
    populations gene pool.

32
How Does Evolution Work?
  • Populations (group of organisms that belong to
    the same species) change over time and evolve,
    not individual organisms (unlike Lamarcks idea)
  • Mutations (small changes in the nucleotide
    sequence of DNA) result in new traits and
    increasing variation in the population
  • One mutation alone usually does not change the
    population, however, beneficial mutations can
    change the population

33
How Does Evolution Work?
  • Genetic drift change in the allele frequency in
    a population based on chance
  • Founder effect small group of organisms move
    away from the main population and give rise to a
    new population
  • Bottleneck effect after a natural disaster, a
    small group of organisms with different
    characteristics survive

34
How Does Evolution Work?
  • Gene flow
  • movement of organisms from one population to
    another
  • Natural selection (this is already familiar)
  • Nonrandom mating coolness
  • For example males with the largest or most
    colorful adornments are often most attractive to
    females.
  • May pose some risks? male birds with flashy
    colors may be more visible to predators but
    every time a female chooses a mate based on
    certain appearance or behavior, she perpetuates
    the alleles that caused her to make that choice
    and allows a male with a particular phenotype to
    perpetuate his alleles.

35
How Does Evolution Work?
36
Modern Evolutionary Theory
  • Several scientists improved on Darwins theory
    and this improvement is still going on.
  • Today we explain the reasons for evolution with
    mutations, changes in DNA and sexual
    reproduction.
  • Evolution is closely related to genetics.
  • Genetic change in a population or species over
    generations all the changes that transform life
    on Earth the heritable changes that have
    produced Earths diversity of organisms.
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