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COMMON MISCONCEPTIONS ABOUT EVOLUTION
COMMON MISCONCEPTIONS 1 Evolution is “just” a theory
Evolution is “just” a theory
•Scientific theories backed by multiple lines of evidence
•Provide overarching explanation for major aspects
of natural world
•Other scientific theories •Gravity •Plate tectonics •Germ
theory
•Evolutionary theory overwhelmingly accepted by scientists
Scientific Theories
•Scientific Theory •Powerful, broad explanation of a large set
of
observations
•Rests on many well-tested hypotheses
•Makes predictions
•Generates additional hypotheses • Note: CSI, Sherlock Holmes –
“I have a theory about who
killed the victim.” Incorrect! “They have a(n) hypothesis!”
Scientific Theories
• A scientific theory is an explanation of a set of related
observations based on well-supported hypotheses from several
different, independent lines of research.
• Ex. The Germ Theory of Disease arose from the accumulated
observations of scientists such as Pasteur and Koch.
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Other Biological Theories
•Cell Theory
•Bioenergetics
•Homeostasis
•Germ Theory of Disease
•Theory of Genetics – information transfer
•Ecosystem Theory
COMMON MISCONCEPTIONS 2 Evolutionary biologists understand
everything about the history of life
Evolutionary biologists understand everything about the history
of life
•Biologists continually discover new aspects of life
•All evidence fits within context of evolution COMMON
MISCONCEPTIONS 3 Evolution explains the origin of life
Evolution explains the origin of life
•Evolution deals with how life has changed after it
originated
•Other scientific fields address the origin of life
COMMON MISCONCEPTIONS 4 Evolutionary biologists search for
missing links
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Evolutionary biologists search for missing links
•Biologists expect the fossil record to be incomplete
•Finding direct ancestors is unlikely
•Available evidence strongly supports relationships between
current and past species
•Relationships shed light on how traits evolved
COMMON MISCONCEPTIONS 5 Evolution violates the second law of
thermodynamics
Evolution violates the second law of thermodynamics
•Holds that disorder increases in closed systems
•Earth is not a closed system
•Sun provides constant input of energy
COMMON MISCONCEPTIONS 6 Evolution is natural selection
Evolution is natural selection
•Natural selection is a mechanism of evolutionary change
•Other mechanisms:
•Genetic drift
•Sexual selection
COMMON MISCONCEPTIONS 7 Evolution is entirely random
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Evolution is entirely random
•Evolution includes random and non-random components •Mutations
are random
•Natural selection is the non-random spread of particular
mutations
•Convergent evolution demonstrates that evolution is non-random
•Phenotypes are predictable when environments are
similar
COMMON MISCONCEPTIONS 8 Organisms evolve adaptations they
“need”
Organisms evolve adaptations they “need”
•Evolution cannot identify needs
•Mutations do not occur because they would be adaptive in an
environment
• If beneficial mutations happen to occur they may increase in
frequency through selection
COMMON MISCONCEPTIONS 9 Evolution is a march of progress
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Evolution is a march of progress
•Evolution is not ladder-like
•New species result from branching events
COMMON MISCONCEPTIONS 10 Evolution always moves from simple to
complex
Evolution always moves from simple to complex
•Evolution can also move from complex to simple
•Lizards snakes
Ambulocetus Rodhocetus
Basilosaurus
Balaenoptera (blue whale)
COMMON MISCONCEPTIONS 11 Evolution results from individuals
adapting to environment
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Evolution results from individuals adapting to environment
•Evolution only works on inherited traits
•Acquired changes are not passed to offspring
•Populations evolve; individuals do not
•Evolution results from changes in allele frequencies
COMMON MISCONCEPTIONS 12 Organisms are perfectly adapted to
their environment
Organisms are perfectly adapted to their environment
•Natural selection can only work with available variation
•Constrained by physics and development
•Many traits involved in trade-offs
•e.g. guppy brain size
Adaptive Evolution
• Natural selection does not result in a perfect match between
organisms and their environments, partly because environments are
constantly changing.
• Also, there are several constraints on evolution:
1. Lack of genetic variation 2. Evolutionary history 3.
Ecological trade-offs 4. Physical, developmental constraints -
mechanical
Adaptive Evolution
1. Lack of genetic variation: If there is no beneficial allele,
adaptive evolution at that gene can not occur. • Example:
Initially, a mosquito population
lacked alleles that provided resistance to pesticides, so the
pesticides were effective.
• Advantageous alleles arise by chance, not “on demand.”
• Resistance gene arose by random mutation. Pesticides were
ineffective against mosquitoes that carried the mutation.
Adaptive Evolution
2. Evolutionary history: Natural selection works on the traits
already existing in organisms.
• Organisms have certain characteristics and lack others because
of their ancestry.
• Example: Dolphins evolved from terrestrial mammals; they have
lungs and cannot “breathe” underwater.
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Adaptive Evolution
•Natural selection can bring about great changes, such as the
mode of life and streamlined body form of the dolphin.
•But it does so by modifying traits that are already present,
not by creating advantageous traits de novo.
Panda’s thumb: Co-opt a ready-made structure for another use;
may not be “best” solution, but it works and didn’t take a lot of
new developments
Physical laws can constrain evolution of trait
Limit size (large and small)
Evolution takes the easy way out
Adaptive Evolution
3. Ecological trade-offs: All organisms face trade-offs in
allocation of energy and resources to growth, reproduction, and
survival.
• Adaptations represent compromises in the abilities of
organisms to perform different and sometimes conflicting
functions.
Adaptive Evolution
4. Physical constraints: mechanical problems. Physical laws can
constrain evolution of trait
• Limit to size (large and small). Ex. Limit to size of
arthropods because exoskeleton would become too heavy to support
since muscles are all attached to it.
COMMON MISCONCEPTIONS 13 Evolution happens for the good of the
species
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Evolution happens for the good of the species
•Evolution selects traits that are beneficial for individuals or
their genes
•Traits that are bad for individuals (or genes) will not be
selected even if they are good for the species
COMMON MISCONCEPTIONS 14 Evolution promotes selfishness and
cruelty
Evolution promotes selfishness and cruelty
•Natural selection favors traits that increase reproductive
success
•Different conditions select for different traits
•Cooperative traits are beneficial under some conditions
COMMON MISCONCEPTIONS 15 Evolution seeks peaceful harmony in
nature
Evolution seeks peaceful harmony in nature
•Natural selection favors traits that increase reproductive
success • Can result in exploitation COMMON
MISCONCEPTIONS 16 Life can be divided into higher and lower
forms
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Life can be divided into higher and lower forms
•All of life is adapted to the environment in numerous ways
•Environments differ so adaptations differ
•One adaptation is not “superior” to another adaptation
All organisms are connected by the passage of genes along the
branches of the phylogenetic Tree of Life.
COMMON MISCONCEPTIONS 17 Evolution has produced a stable
diversity of life
Evolution has produced a stable diversity of life
•Extinction means diversity is not stable • 99% of all species
that ever existed
are extinct