Transcript Evolution

Evolution
Evolution
A
process of change
through time.
Theory of Evolution
1.
2.
Suggests that existing forms of
life on earth have evolved from
earlier forms over long periods of
time.
Evolution accounts for the
differences in structures,
function, and behavior among life
forms as well as changes that
occur in populations over many
generations.
(I) Evidence of Evolution
Observations
supporting the
theory of organic evolution can
be made through the study of:
1. Geologic record
2. Comparative Cytology,
Biochemistry, Anatomy, and
Embryology
(A) Geologic Record
Earth is between 4.5 to 5 billion
years old (age was determined
by radioactive dating of rocks).
2. Fossils- are the remains of traces
of organisms that no longer
exist.
Fossils have been preserved in
ice, sedimentary rock, amber,
and tar.
1.
3. Other fossils have been formed from
petrification, a process by which the tissues
are gradually replaced by minerals that
produce a stone replica of the original
material.
4. Imprints, casts, and molds of organisms or
parts of organisms are frequently found in
sedimentary rock.
5. In undisturbed layers (strata) of sedimentary
rock, the lower strata contain old fossils
while the upper strata contain younger fossils
(B) Comparative Anatomy
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Evidence supports that similarities of basic
structures exist between different organisms.
Homologous structures are anatomical parts
found in different organisms in origin and
structure.
The presence of such homologous structures
suggest that these organisms have evolved from a
common ancestor.
(C) Comparative
Embryology

Although certain
adult organisms
may be different
from each other, a
comparison of the
early stages of
their embryonic
development may
show similarities
that suggest a
common
ancestor.
(D) Comparative Cytology
All living things are made up
of cells.
2. Cell organelles including the
cell membrane, ribosome's,
and mitochondria are
structurally and functionally
similar in most organisms.
1.
(E) Comparative Biochemistry
All
living things contain similar
biochemical compounds.
Examples would include:
structure and function of DNA,
RNA, and proteins (including
enzymes) are similar in all
organisms.
(II) Theories of Evolution
Attempts to explain the
similarities and differences
among species.
2. Adaptations- are a major
component to these theories.
Adaptations are features which
make a species better suited to
live and reproduce in its
environment.
1.
(A) Lamark
 The
evolutionary theory of JeanBaptiste Lamark was based on the
principle of:
1. Use and Disuse
2. Inheritance of acquired traits
Principle of Use and Disuse
 For
an organism, new structures
appeared in the course of evolution
because they were needed. Structures
that were present and were used
became better developed and increased
in size; structures that were not used
decreased in size and eventually
disappeared
Ex: muscles of an athlete vs. appendix
Inheritance of Acquired Traits
 Useful
characteristics acquired by an
individual during its lifetime can be
transmitted to its offspring.
 These acquired traits results in
species that are better adapted to their
environment.
 Ex: a giraffe’s neck became longer as
a result of stretching to reach higher
branches. This acquired trait was
then passed down to the offspring .
Lamarck's conception of evolution
(B) Weisman
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2.
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6.
August Weisman did not agree with
Lamark’s theory of acquired traits.
In a series of experiments, Weisman
removed the tails of mice.
The mating of these tailless mice produced
offspring with tails of normal length.
Weisman removed the tails of these mice
and allowed them to mate.
Again, offspring were produced with tails of
normal length.
The acquired condition of “taillessness”
was not inherited.
(C) Darwin
1809-1882

Charles Darwin devised a theory of evolution
based on variation and natural selection.
 Included in hid theory were five main ideas:
1. Overpopulation
2. Competition
3. Survival of the Fittest
4. Reproduction
5. Speciation
Natural Selection
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3.
Natural selection is the evolutionary process which
selects the variation(s) of organisms best suited for
a particular environment.
Natural selection and its evolutionary
consequences provide a scientific explanation for
the fossil record of ancient life, as well as for the
molecular and structural similarities
observed among the diverse species of living
organisms.
The degree of kinship between organisms or
species can be estimated from the similarity of their
DNA sequences; this similarity often closely
matches organisms' or species' classification based
on anatomical similarities.
DNA Sequence Similarities in Some Primates
The graphic above shows that:
1.All of these primates had a common ancestor, the
ancestral primate.
2.The human and chimpanzee have the closest
evolutionary relationship as their DNA is the most similar.
Overpopulation
Within
a population, there are
more offspring produced in
each generation than can
possibly survive.
Competition
 Natural
resources; like food,
water, and space available to a
population is limited.
 Because there are many
organisms with similar nutritional
requirements, there must be
competition between them for the
resources needed to survive.
Survival of the Fittest
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Variations among members of a population make
some of them better adapted to the environment
than others.
It is generally the best-adapted individuals that will
survive.
The environment is the agent of natural selection
determining which species will survive.
The individuals who survive are the ones best
adapted to exist in their environment due to the
possession of variations that best suit them to their
environment. This genetic variability within a
species is chiefly due to mutation and genetic
recombination. The variation of organisms within a
species increases the likelihood that at least some
members of the species will survive under
changed environmental conditions.
Reproduction
Individuals
that survive
and then reproduce
transmit these variations
to their offspring.
Speciation
As time and generations continue,
adaptations are passed on and new
species may evolve from a
common ancestor.
 Ex: caveman  present man
1.
• Small differences between parents and offspring can
accumulate in successive generations so that
descendants become very different from their
ancestors.
• An adaptation is a variation which assists an
organism or species in its survival. Biological
adaptations include changes in structures, behaviors,
or physiology that enhance survival and reproductive
success in a particular environment.
• Some characteristics give individuals an advantage
over others in surviving and reproducing, and the
advantaged offspring, in turn, are more likely than
others to survive and reproduce. The proportion of
individuals that have advantageous characteristics will
increase.
• Behaviors have evolved through natural selection.
The broad patterns of behavior exhibited by organisms
have evolved to ensure reproductive success.
Modern Examples of Natural Selection
Peppered moth:
• two varieties of peppered moth existed,
a light colored and a dark colored one
• as industrialization and coal burning increased, the
environment in England where these moths lived became
dirtier
• the dark colored variety of the moth blended into the
trees and increased in numbers, while the light colored
moth was less adapted and decreased in numbers.
Insect resistance to insecticides:
• Insecticides kill insects not resistant to the insecticide,
while insects resistant to the insecticide live to reproduce.
The insecticide acts as a selecting agent.
Bacterial resistance to antibiotics:
• Bacteria not resistant to an antibiotic are killed by it,
while resistant bacteria live to reproduce. The antibiotic is
a selecting agent for these bacteria.
(III) Evolution and Extinction
 Evolution does
not necessarily mean long
term progress is going to go in a certain
direction.
 Evolutionary changes often appear to be
like the growth of a bush. Some branches
survive from the beginning with little or no
change, many die out altogether, and others
branch out repeatedly, sometimes
giving rise to more complex organisms.
Direction of Evolution
Note the divergence of the various groups from a
common ancestor and the fact that some branches
became extinct.
• Extinction of a species occurs when the
environment changes and the
adaptive characteristics of a species are
insufficient to allow its survival.
• The fossil record indicates that many
organisms that lived long ago are extinct.
• Extinction of a species is common; most of
the species that have lived on earth no longer
exist.
(IV) Modern Theories of
Evolution
 The
modern theory of evolution
includes both Darwin’s ideas of
variation and natural selection and the
current knowledge of the sources of
variations.
(A) Sources of Variations
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Segregation and the recombination of
alleles during sexual reproduction.
Mutations are random changes in the genes
or DNA of sex cells may result in new gene
combinations creating variation in the
offspring formed from these.
Only mutations that occur in sex cells can be
passed on to the offspring. Mutations which occur
in other cells can be passed on to other body
cells only.
The experiences an organism has during its lifetime
can affect its offspring only if the genes in its own
sex cells are changed by the experience.
1. Variation and Evolution

Evolution is the consequence of the following
factors:
1. The potential for a species to increase its numbers
2. The genetic variability of offspring due to mutation
and recombination of genes
3. A finite supply of the resources required for life
4. The ensuing selection by the environment of those
offspring better able to survive and leave offspring.
 Some characteristics give individuals an advantage
over others in surviving and reproducing, and the
advantaged offspring, in turn, are more likely
than others to survive and reproduce. The
proportion of individuals that have advantageous
characteristics will increase.
An Example of Variation Driving Natural Selection
Natural selection favors longer necks better chance to get
higher leaves. Favored character passed on to next generation.
Original group
exhibits variation
in neck length.
• The variation of organisms within a species increases the likelihood that at least
some members of the species will survive under changed
environmental conditions.
• The great diversity of organisms is the result of billions of years of selection for
favorable variations that has filled available niches of our planet with life forms.
(C) Geographic Isolation
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Gene frequency- the percentage of
organisms in a population that carry an
allele.
Isolation of a population increases the
chances for speciation (the development of
a new species) by separating a small group
of organisms from the main population with
its large gene pool (inheritable traits).
Changes in gene frequency are more likely
to occur in small populations than in large
ones.
Geographic isolation of a population is
caused by natural barriers like mountains,
large bodies of water, and deserts.
(D) Reproductive Isolation
 If
the isolated population
becomes so different from the
main population that members of
the two cannot interbreed and
produce fertile offspring, then
they have become two distinct
species.
(E) Time Frame for Evolution
 There
are two different theories
proposed by scientists to address the
rate of evolution:
1. Gradualism- proposes that
evolutionary change is slow, gradual,
and continuous.
2. Punctuated Equilibrium- proposes
that species have long periods of
stability (several million years)
interrupted by geologically brief
periods of significant change during
which a new species may evolve.
Gradualism
Punctuated
Equilibrium
