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Natural Selection


Natural Selection True or False Evolution is a theory about the origin of life. Important Vocabulary 1. Species: A group of organisms whose individuals can breed ... – PowerPoint PPT presentation

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Title: Natural Selection

Natural Selection
True or False
Slide 2
  1. Evolution is a theory about the origin of life.

2. Organisms are always getting better through
False no perfect organism
3. Natural selection involves organisms trying
to adapt
False results from genetic variation
4. Evolutionary theory is invalid because it is
incomplete and cannot give a total explanation
for the biodiversity we see around us.
False All scientific theories are works in
progress . As new evidence is discovered,
theories are revised or even disproven
Source http//
Important Vocabulary
Slide 3
  • 1. Species A group of organisms whose
    individuals can breed together to produce fertile
  • 2. Population A localized group of individuals
    belonging to the same species.
  • 3. Evolution A slow change in a population over
  • 4. Adaptation any structural or physiological
    change that gives an organism an advantage in the
  • Examples structural stingers, thorns,
  • physiological being
    heterozygous for sickle cell anemia
    (protection against malaria),
    endotherms maintain constant
    body temp can live in colder climates
    than amphibians and reptiles

Charles Darwin His Journey and Observations
Slide 5
  • Charles Darwin explained how Natural Selection
    could cause a population to adapt and change over
    time. (note he states- a population will
    change -not an individual)

Route of Darwins 5 Year Trip
Slide 6
Galapagos Islands
Darwin spent a lot of time and collected a lot of
specimens from the Galapagos Islands.
Charles Darwin An Unlikely Evolutionist
Slide 7
  • Who was Charles Darwin?
  • 1809 English naturalist
  • Went on a 5 year voyage on the HMS Beagle as an
    unpaid scholar
  • Collected plants animals during journey
  • Darwin did not set out to develop a theory of
  • Observations and specimens collected helped
    Darwin formulate his theory of evolution

Charles Darwin
Darwins Observations
Slide 8
  1. In Argentina, Darwin saw earthquakes raising the
    earth several feet
  2. Shells of marine animals found far inland at
    great heights in Andes Mts
  3. Fossils of huge sloths armadillo-like animals
    (both extinct) similar to modern forms
  4. Animals on Galapagos were similar but not same as
    those on mainland S. America Antarctica
  • Galapagos penguin
  • 14 inches tall
  • 5 lbs
  • Eat small fish sardines
  • Nests in burrows
  • Chinstrap penguin
  • 28 inches tall
  • 9-14 pounds
  • Eat small fish krill
  • Build nests out of small stones

Darwins Observations on the Galapagos Islands
Slide 9
  1. Fewer types of organisms on the islands
  2. Island species differ from mainland species
    from island to island
  3. Finches on Galapagos resemble mainland finch, but
    there were more types on the islands

Ideas that Shaped Darwins Thinking
The Work of Lyell Influenced Darwins Ideas
Slide 11
  • Charles Lyell English geologist
  • 1830 On the Principles of Geology
  • Natural forces processes that shaped ancient
    Earth are the same forces acting on Earth today.
  • EX Rain erodes mountains molten rock
    pushes up to create new ones.
  • Earths geologic features formed as a result of
    gradual processes.
  • Must take millions of years to change geography
  • 2. Darwin read Lyells work while on his voyage
    agreed with Lyells conclusions

Charles Lyell
The Work of Malthus Influenced Darwins Ideas
Slide 12
  • 1798 Thomas Malthus --Economist
  • Essay on the Principle of Population
  • Said that plants and animals tend to have more
    offspring than nature can support
  • Food production increase at a slower rate than
  • Darwin read Malthuss essay after he returned
    from his voyage
  • Darwin concluded that all organisms produce more
    offspring than the population can support

Thomas Malthus
Old Theories of EvolutionLamarcks Theory of
Use and Disuse
Slide 13
  • 1801 Theory of Inheritance of Acquired
  • Theory of inheritance of acquired
    characteristics Use and disuse
  • If an organism changes in order to adapt to its
    environment, those changes are passed on to
  • (We now know that organisms cannot change or
    adapt to their environment)
  • Said that changes in organisms occur to help an
    organism reach perfection.
  • Problem No organism is perfect

Zoologist came up with the word
invertebrate. Most scientists thought these
creatures were too lowly to study
Example of Lamarcks Hypothesis
Slide 14
  • Example of Lamarcks hypothesis
  • Male crab uses small front claw to ward off other
  • Because it has been used a lot, front claw
    becomes larger.
  • Larger claw trait is passed on to offspring.

Even though his hypothesis is flawed, he was the
first to address the fact that organisms adapt to
their environment
Darwin explained Evolution by Natural Selection
Slide 15
  • 1859 Darwin published On the Origin of Species
  • Proposed that natural selection was the mechanism
    for evolution.
  • Individuals vary in one or more traits there
    can be slight differences in their ability to
    survive reproduce.
  • Nature selects those individuals w/ favorable
    traits to leave more offspring that are better
    suited (FIT) for their environment.

Published 25 years after Darwin wrote it!
The Evidence that Darwin used to Develop the
Evidence that Supports Evolution Fossil Record
Slide 17
  • 1. Fossil preserved remains (bones, teeth,
    shells) or evidence (imprint or footprint) of
    ancient organisms.
  • Fossils found in sedimentary rock
  • Younger sediments deposited on top of older
  • Older sediments contain older, simpler fossils
  • Younger sediments contain younger, more complex
  • Fossils found in sediments of organisms that are

Trilobites are extinct!
Evidence that Supports Evolution Geographic
Distribution of Living Species
  • 1. Biogeography the geographical distribution
    of species in relation to geography and other
  • 2. Influenced by continental drift

Flying squirrels and sugar gliders look similar,
but are only found on their respective
continents. Similarities in appearance are due to
development under similar selection pressures.
Evidence that Supports Evolution Homologous
Slide 19
  • 1. Homologous structures similar structures but
    different functions
  • Structures develop from same clump of embryonic
  • Provides evidence that four-limbed vertebrates
    descended from a common ancestor.
  • 2. Vestigial structures structures or organs
    that are reduced in size do not seem to serve a
    useful function
  • 3. Homologous vestigial structures imply that
    common genes are involved.

Homologous structures forelimbs of vertebrates
Pelvis femur bones are vestigial in whales
Evidence that Supports Evolution Similarities
in Embryology
Slide 20
  • The embryos of vertebrates are very similar
    during early development.
  • All vertebrate embryos have 1.)
    Notochord, 2.) dorsal hollow nerve cord, 3.)
    pharyngeal slits, and 4.) post-anal tail
  • 2. The same groups of embryonic cells develop in
    the same order and in similar patterns to produce
    tissues organs.
  • 3. Common cells tissues growing in similar ways
    produce homologous structures.
  • 4. Implies that common genes are involved.

Post Darwin DNA Evidence Supports Evolution
We can compare DNA sequences to which are most
closely related
We can compare amino acid sequences to which are
most closely related
Why didnt Darwin use DNA evidence in developing
his theory?
It had not yet been discovered!
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