Transcript Biology-Unit 15powerpoint evolution

Biology-Unit 15
The Theory of Evolution
• Evolution- The process of change over
time
• Theories of evolution assume that modern
life forms have evolved (changed) from
previously existing life forms.
1. Evidence of Evolution
• Attempts to describe the mechanisms by
which organisms change over time have
formed the basis of the evolutionary
theory.
Evidence of
Evolution
includes
The fossil
record
which is composed of
Physical
remains of
organisms
Geographic
distribution of
living species
Homologous
body
structures
Similarities
in early
development
which indicates
which implies
which implies
Common
ancestral
species
Similar genes
Similar genes
Theories of Evolution
• Attempt to explain the diversity of life
forms on earth
• Species diversity is actually based on the
variety of ADAPTATIONS that different
species may possess.
• Adaptations - any structural, functional, or
behavioral characteristic of a species that
helps it to better survive in its
environment
Evidence of Evolution continued:
A. Comparative Cytology
-Organisms with very similar cell
structures are usually considered to be
more closely related.
B. Comparative
Biochemistry
-Analysis of enzymes
and other proteins
show that a great
deal of similarity
exists in organisms
known to be related
genetically.
C. Comparative
Anatomy
-Similar organisms
can be shown to have
limbs, internal organs,
or other structures
that are constructed
similarly.
-These structures are
known as homologous
structures.
D. Comparative
Embryology
-Reproductive
processes in many
different organisms
reveal patterns of
similarity among
closely related
organisms.
E. Geologic Record
Fossils are commonly discovered in
sedimentary rock layers.
Water carries
small rock
particles to lakes
and seas.
Dead organisms are
buried by layers of
sediment, which forms
new rock.
The preserved
remains may
later be
discovered and
studied.
-The oldest fossils of the simplest life forms
are generally found in the bottom layers.
-While the younger fossils of more complex
organisms are found in the top layers.
-This is an example of relative dating.
Scientists can determine the age of
fossils through radioactive dating.
Sedimentary
rocks form in
horizontal layers
When part of Earth’s crust is
compressed, a bend in a rock
forms, tilting the rock layers.
As the surface erodes due to
water, wind, waves, or glaciers,
the older rock surface is
exposed.
New sediment is
then deposited
above the exposed
older rock surface
• F. Vestigial Structures: structures that do not
•
•
seem to have any use (are also reduced in size)
but are remains of structures that were probably
functional in ancestral organisms.
Human examples: appendix, tailbone (coccyx),
wisdom teeth, muscles that move the ears and
nose
Animal examples: whales and pythons have
vestigial hind leg bones embedded in body wall
2. Evolutionary Scientists:
A. John Lamarck - Proposed the idea of
evolution that included two main ideas:
1. Use and Disuse
-The more a structure was needed, the
more efficient it would become.
-A structure that was not used would
eventually disappear.
2. Transmission of Acquired Traits
-Traits developed as needed within the
life of an organism.
• An organism could
•
pass these “acquired
traits” to future
generations through
the process of
reproduction.
The favorable
“adaptations” would
result in improved
survival ability for the
species.
• Lamarck’s theories were an important
First Step in the development of a
scientific view of the evolutionary
process.
• Later Experiments conducted by
August Weismann and others failed
to support Lamarck’s theories.
C. Charles Darwin
• 19th Century naturalist
from England
• Devised a theory of
evolution based on
variation and natural
selection.
• His theory forms the basis
of the modern theory of
evolution.
Darwin’s Five Main Ideas:
1. Overproduction: species have a tendency to
produce far more offspring than can possibly
survive.
2. Competition: Within each species there is a
struggle for survival that may eliminate many
individuals before they reach reproductive
maturity.
3. Variation: Darwin noticed variation within a
species even though he could not explain. He
knew nothing of genes.
4. Survival of the Fittest: Animals better
able to resist disease, withstand
environmental conditions, and produce
more offspring are more likely to survive.
5. Reproduction: Adaptive advantages of
one generation may be passed on to the
next, perpetuating them in the species.
-This process is known as SPECIATION
Lamarck and Darwin
compared
• Lamarck: Giraffes have long
necks due to years of
stretching to reach leaves on
tall trees and the passing on
of the long necks to
offspring.
Lamarck and Darwin
compared
• Darwin: Giraffes necks naturally vary in length.
Those giraffes that possess a long neck were
able to reach the leaves on the tall trees and
survive. They then passed the gene for a long
neck on to their offspring.
D. Modern Evolutionary Theory
• Based primarily on Darwin’s theory of
natural selection.
• In addition it incorporates the information
available from the mechanisms of
genetics.
Five Main Ideas:
1. Production of variation
-The reproductive process, meiosis and
fertilization provide the method by which new
combinations of both old and new traits may be
“tried out” as new varieties within a species.
-Mutation
-An important process in providing the new
genes that may lead to the production of new
traits.
2. Natural Selection
• Individuals that survive are “selected”
and are assumed to be those best
adapted to survive under the particular
set of environmental conditions.
• Survivors tend to pass on the genes
associated with their adaptive
advantages.
3. Speciation
• When enough unique adaptations have
been accumulated, in a species’
population, a new species arises from
the parent species.
4. Reproductive Isolation
• If two populations of species are
geographically separated from each
other for a sufficiently long period, they
may change so greatly that even if
geographic barriers are removed the two
species will not be able to interbreed and
reproduce.
or, another example… the “Founder Effect”
Time Frame for Evolution
– Gradualism – Assumes that evolutionary
change is slow and gradual, and continuous.
-Supported by fossil records
-Gradual change of organisms seen
from each sedimentary layer
• Punctuated Equilibrium – Assumes that
species experienced long geographic
periods of stability (millions of years or
more) in which little or no change
occurred.
• This stability is “punctuated” by brief
periods (a few thousand years) in which
dramatic changes occur within a species.
• Punctuated equilibrium is supported by
fossil evidence in which little change is
noted between most sedimentary layers
but sudden “bursts” of change are evident
in the fossils of a few sedimentary layers.
Heterotroph Hypothesis – how life began
-Assumes that the first primitive life forms
were not able to manufacture their own
food.
-Heterotrophs… (they had to eat)
Conditions of the Early Earth
 Earth formed from clouds of
cosmic dust and gas over 5 billion
years ago.
 After condensing to a semi-solid
form, the earth required hundreds of
millions of years to cool.
 During that period, the earth remained a hot
environment filled with simple inorganic
substances such as H2O, NH3, CH4,
and H2
-These substances were mixed together in the
primitive atmosphere and oceans to form a
“HOT, THIN SOUP” in which random
chemical reactions could occur at a rapid rate.
• It is believed that these random chemical
reactions led to the synthesis of simple
sugars, lipids, and amino acids which then
formed larger molecules.
• The large molecules came together to
form aggregates which are assumed to
have formed the first simple cell-like
organisms “living” able to reproduce.
• Stanley Miller
-Set up a controlled environment that
simulated the hot, thin soup theory
-He was able to make simple organic
substances.
Mixture of gases
simulating
atmospheres of
early Earth
Spark simulating
lightning storms
Cold water cools
chamber, causing
droplets to form
Water vapor
Water vapor
Liquid containing
amino acids and other
organic compounds
-The natural by-products of living cells is CO2.
-Organisms evolved to use the CO2 to make
their own organic food. These were the first
autotrophs!
-These pioneer autotrophs produced free O2
which was released into the atmosphere.
-This is the first photosynthesis!
Evolution of Life
• Early Earth was hot; atmosphere
contained poisonous gases.
• Earth cooled and oceans condensed.
• Simple organic molecules may have
formed in the oceans.
• Small sequences of RNA may have formed
and replicated.
• First prokaryotes may have formed when
RNA or DNA was enclosed in
microspheres.
• Later prokaryotes were photosynthetic
and produced oxygen.
• An oxygenated atmosphere capped by the
ozone layer protected Earth.
• First eukaryotes may have been
communities of prokaryotes.
• Multicellular eukaryotes evolved.
• Sexual reproduction increased genetic
variability, hastening evolution.