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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