Transcript Biology TEKS 7A & 7B

Theory of Evolution
Identify evidence of change in species
using DNA sequences, anatomical
similarities, physiological similarities,
embryology and fossils
 Illustrate the results of natural selection
(changes) in speciation, diversity,
phylogeny, adaptation, behavior and
extinction
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Evolution
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Evolution: change in the traits of a species over time
Species: a group of organisms who can produce fertile
offspring
Charles Darwin: developed the theory of evolution called
Natural Selection
Natural Selection states that:
 there is variation (differences) within populations
 some variations are favorable (favorable variations
improve an organism’s ability to function and reproduce in
its own environment)
 not all young produced in each generation can survive
 individuals that survive and reproduce are those with
favorable variations; these individuals can then pass on
the favorable traits to their offspring
Evidence to Support Evolution:
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DNA: by comparing the DNA sequences of two organisms or the amino acid
sequences made from the DNA, scientists can learn which organisms are
related; the more DNA two organisms have in common, the closer related
they are
•Using the table, compare the amino acid
sequence of the chimp and the human.
•Notice that for this protein the chimp and
human have the exact same sequence.
•Now compare the baboon and the human.
•Notice that there are 5 differences in the
sequence.
•This tells you that the human is more
closely related to the chimp than the
baboon.
Anatomical similarities
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An inherited trait that increases the
population’s chances of survival and
reproduction is an adaptation
 homologous
structure: same structure
with different functions found in different
species and thought to be inherited from
common ancestors
ex: humans, whales, and bats all have the same # and type of
bones in the forelimbs but their functions are different
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Analogous structures have the same function,
but different structures & do not show a close
relationship
ex: insect wing and bird's wing
Embryology
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Similarity in embryo development shows a close
relationship (vertebrate embryos all have tail &
gill slits)
Fossils
These are imprints
or remains of living
things.
 In undisturbed layers
of sedimentary rock,
the deeper it is, the
older it is.
 Give us information
about extinct
species.
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Adaptation
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mimicry: an organism can copy the appearance of
another organism; in one form of mimicry, a harmless
species has adaptations that result in a physical
resemblance to a harmful species; predators that avoid the
harmful looking species also avoid the similar-looking
harmless species.
 camouflage: an organism can blend into the surroundings
Variation
the differences between individual
members of a population (ex: fur color, eye
color, etc.)
 cannot always be observed
 are almost always genetically inherited
 results from mutations and recombination
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Speciation
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Speciation: the evolution of a new species
when the production of fertile offspring in a
species is somehow prevented; it can occur in
several ways:
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Geographic Isolation: physical barriers separate members
of a population so that they can not reproduce; these barriers
can be caused by changes in climate, volcanic eruptions, or
changes in sea level; the separate groups become more and
more distinct and eventually become separate species
Polyploids: mistakes in meiosis cause the chromosome
number in individuals to change; when a polyploidy organism
mates with a normal individual, the zygotes do not develop
normally; this type of speciation is more common in plants
Speciation
new species
species
original species
Types of Evolution:
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adaptive radiation: when a species is
introduced to a new environment, several new
species evolve
convergent evolution: distantly related
organisms evolve similar traits
directional selection: occurs when natural
selection favors one of the extreme variations of
a trait.
disruptive selection: individuals with either
extreme of a trait’s variation are selected for
Adaptive Radiation
new species
new species
species
new species
new species
new species
Convergent Evolution
species
new species
new species
species
these 2 new species share many traits
Directional vs. Disruptive Selection
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In directional selection, there is a shift in
frequency to an extreme phenotype. In the
example, the environment was changed
so that now it is barren and has dark soil.
rabbit coat color
light
medium
dark
Directional vs. Disruptive Selection
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In disruptive selection, the most common
variation in a population is not favored. In
the example, light-colored bushes have
begun to grow in the dark soil.
rabbit coat color
light
medium
dark
Phylogeny
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Phylogeny: the evolutionary history of an
organism; this is used to classify organisms into
kingdoms, phyla, classes, etc.; a phylogenetic
tree or cladogram shows how organisms are
related to one another and how they evolved
examples of phylogenetic trees
Behavior
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Behavior: anything an animal does in response to a
stimulus; types of behaviors include:
innate behaviors: inherited behaviors
reflex: simple innate behavior that is automatic (don’t
need to think about it)
instinct: complex pattern of innate behaviors that begins
when an animal recognizes a stimulus and continues
until all parts of the behavior have been completed
territorial behavior: behavior in which animals will
defend their space by driving away others of the same
species
aggression: behavior that is used to intimidate another
animal of the same species
Extinction
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A population is extinct when the last of that
species is dead.
Example: There are no more dinosaurs.
What happened? Their habitat was destroyed.
When they no longer have what they need to live,
they die.