Transcript Evolution

History of Evolution
• James Hutton & Charles Lyell
• Hutton - rocks are in layers, which form
very slowly; proposed that the
Earth is millions of years old.
• Lyell - geological features were formed by
processes that still occur today.
~ mountain building, volcanoes,
erosion, etc.
Jean-Baptiste Lamarck
• He proposed that by selective
use/disuse of organs, organisms
acquired or lost certain traits during
their lifetime.
• These traits could then be passed on to
their offspring; which, over time, led to
change in a species.
Lamarck’s Key Ideas
• 1.) Tendency toward perfection.
• He believed that all organisms try to become
perfect by acquiring traits that help them live
more successfully.
• Ex: In his view, the ancestors of birds had an
urge to fly. Over many generations, they kept
trying to fly, and their wings increased in size
and eventually became good enough to allow
flight.
Lamarck’s Key Ideas
• 2.) Use and Disuse
• Organisms can change the size and shape of
parts of their bodies by using them in different
ways.
• Ex: By trying to use their front limbs for flying,
birds eventually were able to change those
limbs into wings.
• The reverse is also true, according to Lamarck
Lamarck’s Key Ideas
• 3.) Inheritance of Acquired Traits
• If an animal can change its body during its lifetime, its
offspring will also have these changes.
• If an animal was able to change its body to get a longer
neck (say, by stretching it), its offspring will also have
longer necks.
• However, by this reasoning, if you were to chop off your
arm, your children should be born missing an arm
because they should inherit this trait.
Evaluating Lamarck
• He was incorrect in many ways.
• He did not know how traits were inherited.
• He did not know that an organism’s behavior
has no effect on its inheritable characteristics.
• But, he was one of the first to develop a
scientific hypothesis for evolution and realize
that organisms are adapted to their
environments.
Darwin and Natural
Selection
Who was Darwin?
• Charles Darwin
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Naturalist
Scientist
Wanted to be a priest
Quit medical school to study the Bible and
become a priest.
The Voyage…
• 1831
• 5 year trip on the HMS Beagle around
the world to study life forms.
• Stopped in Brazil, Peru, Ecuador, the
Galapagos Islands, New Zealand,
Australia
His Observations
• Patterns of diversity.
• He saw similar ecosystems with very
different looking animals.
• Ex: Australia and Argentina have very
similar grasslands, but the animals in each
are very different.
• No rabbits in Australia; no kangaroos in
Argentina.
His Book
• On the Origin of Species
• 1859
• Summarized the results of his voyage and later
studies.
• Proposed a mechanism for evolution called natural
selection
• Presented evidence demonstrating that evolution
has been taking place for millions of years, and
continues today in all living things.
Controversy
• His book caused an immediate
sensation (think: The Da Vinci Code of
its time.)
• Many people argued about his
statements.
• Some people thought he was brilliant;
others thought he was an idiot/heretic.
• But, WHAT did Darwin actually say?
Darwin’s Big Idea
Natural Selection!!!!
What is Natural Selection?
• It is a mechanism for change in populations
that occurs when organisms with traits that
allow them to survive better reproduce and
pass those traits to their offspring.
• What happens to those organisms who don’t
have the favorable traits?
• They are less likely to survive and reproduce
Natural Selection Summarized
• 1.) In nature, there is a tendency for
organisms to produce more offspring
than can possibly survive.
• Ex: Fish
Natural Selection Summarized
• 2.) In any population, individuals will
have slight differences in their
phenotypes.
• Ex: Fish, zebras, snakes
Natural Selection Summarized
• 3.) Individuals with traits that make
them more likely to survive in an
environment will survive and pass
on those traits to their offspring.
• Fish, zebras and snakes again…
• More of these individuals will survive as
compared to those who do not have the
helpful traits.
Natural Selection Summarized
• 4.) Eventually, the offspring of the
survivors will make up a larger part of
the population.
• Depending on environmental factors,
after many generations, the population
may look completely different from
what it originally was.
Evolution by Natural Selection
• Struggle for existence:
• Members of each species compete for
resources.
• Faster or more adept predators get more
food; faster prey or those with good
camouflage get away and reproduce.
• Adaptations allow organisms to survive.
Evolution by Natural Selection
• Survival of the fittest:
• Those organisms best suited to their environment
will survive; those who aren’t will die.
• Descent with Modification:
• Species today look different from their ancestors.
• Each species today has descended, with changes,
from other species over time.
• All living things are related to one another.
Adaptations
• Any trait that improves the chances of
survival and reproduction is called an
adaptation.
• Species develop adaptations through
natural selection.
Types of Adaptations
• Structural adaptations:
• Physical features that help in survival.
• Ex: thorns of a rose, camouflage, mimicry
• Physiological Adaptations:
• Changes in an organism’ s metabolism
• Ex: antibiotic-resistant bacteria; pesticideresistant insects
Evidence for Evolution
• Fossil Record:
• Fossils were known (even in Darwin’s time) to be
the remains of ancient life.
• Also, it was known that different rock layers
formed at different times in Earth’s history.
• Fossils that are in the different layers are of
different ages; the ones in deeper layers existed
before the ones in more shallow layers.
Evidence for Evolution
• Geographic distribution of living species
• Darwin’s travels
• Different animals on different continents
descended from different ancestors.
• However, because animals on each continent
were living in similar ecosystems and exposed
to similar challenges and pressures, they
developed similar body structures.
Evidence for Evolution
• Homologous body structures:
• Limbs of organisms, for example, have
different forms and functions, but are
made of the same basic bones.
• The same bones in our arms are in the
wings of a bird.
Evidence for Evolution
• Compared Embryology:
• Embryology is the study of embryos, the
early stages of animal development.
• Early in development, the embryos of
different animals are hard to tell apart.
Genes and Variations
How do we get variations in the
gene pool?
Sources of Genetic Variation
• 1.) Mutations
• 2.) Gene shuffling
• Due to sexual reproduction
• Remember: in meiosis, chromosomes/genes
separate (Principle of Segregation)
• Crossing over also leads to variation.
• Think about a deck of cards…
Traits
• The number of phenotypes for a given
trait depends on how many genes
control the trait.
• Single-gene trait vs. Polygenic trait.
Natural Selection and Traits
• N.S. on single gene traits can lead to
changes in allele frequencies, which
leads to evolution.
• Ex: Effect of color mutations on lizard
survival.
Natural Selection on Polygenic
Traits
• When traits are controlled by more than
one gene, the effects of natural
selection are more complex.
• Fitness is the key!
Selection
• Natural selection can effect the
distributions of phenotypes in 3 ways:
• Directional selection
• Stabilizing selection
• Disruptive selection
Directional selection
• Individuals at one end of a curve are
more fit than other individuals.
• This shifts the curve in one direction.
Stabilizing Selection
• Occurs when individuals near the middle of
the curve are more fit.
• The center of the curve stays in the same
place, but the curve becomes narrow.
Disruptive Selection
• Individuals at the ends of the curve are
more fit than those in the middle.
• Creates a “double humped” curve.
Genetic Drift
• Natural selection is not the only source of
evolutionary change.
• In large populations, probability can be used
to predict genetic outcomes.
• In small populations, the laws of probability
do not always work.
• Ex: coin flip
How Does Genetic Drift
Happen?
• In small populations, individuals that
carry an allele for a trait may leave
more offspring (descendants) than
those who don’t have the allele, just by
chance.
• Over time, a series of these chance
happenings can cause an allele to be more
common.
Two methods of Genetic Drift:
• Founder effect
• Bottleneck effect
Founder Effect
* A change in the allele frequencies due to
the migration of a small group of organisms
to a new area.
• Ex: Huntington’s in Venezuela
• Ex: Type O blood in Native tribes in South
America
• Ex: The Amish and Microcephaly in
Pennsylvania
Founder Effect
Bottleneck effect
• Change in allele frequencies due to a
catastrophic event (natural disaster,
disease, habitat destruction, etc.)
Speciation
• The evolution of a new species.
• Geographical isolation can lead to this.
2 Ideas on how evolution
occurs:
• Gradualism:
• Evolution occurs SLOWLY over a long time.
• Adaptations will increase in number
steadily over time.
• Darwin’s idea.
• Punctuated Equilibrium:
• Speciation occurs in rapid bursts followed
by periods of no change.
How do scientists determine
the age of fossils?
• Radioisotope dating
• Isotopes are atoms with different numbers
of neutrons: Carbon 12, Carbon 13, Carbon
14.
• Carbon 14 is the normal isotope used for
dating fossils.
• By measuring the half-life of the isotope,
scientists can determine the age.
Major “Ages” in the History of
the Earth:
Plants respond to the
environment, too.
• Plants do not have nervous systems,
but they do have the ability to respond
to the environment.
Ways plants adapt:
• Geotropism:
• Response of seedlings to the force of gravity.
• Causes roots to grow down and stems to grow up.
• Phototropism:
• Ability of plant to respond to light.
• Thigmotropism:
• Ability of plant to respond to touch.
• Climbing plants use this to find their way
up/around an object.
Geotropism
Phototropism
Thigmotropism
Plant Hormones
• Auxins:
• Responsible for regulating phototropism by
causing cells to get longer.
• Gibberellins:
• Cause plant to grow taller.
• Increase rate of bud formation and seed
germination
• Abscisic acid:
• Inhibit plant growth during times of stress.
Plant Adaptations
• Seeds of some plants will go dormant in
unfavorable conditions.
• Roots and stems are modified into storage
organs.
• Conifers have needles instead of leaves,
which prevent evaporation of water.
• Conifers also have thick bark which insulates
them in the winter.
• Flowers can be pollinated in multiple ways:
wind, animals, birds, insects.
Adaptation Questions
1. Why is it extremely important for plants to be
able to adapt to the environment?
2. How can you remember the differences
between the tree types of plant adaptations?
3. A plant is found that lacks Abscisic Acid, what
is the significance of this finding? How might
it effect the population of this plant in that
particular ecosystem? What if that plant had
no Gibberellins? Auxin?