Transcript What is a Theory - RMC Science Home

Evolution
What is a
theory?
Scientific Definition of a Theory
• A scientific theory summarizes a
hypothesis or series of hypotheses
that have been supported by
repeated testing. It is a valid
explanation of a phenomenon.
Theory
In science a theory is:
1.Explanatory
2.Predictable
3.Testable
Germ Theory
Using our three criteria for a
theory, let’s see if the
existence of germs is a
theory.
In science a theory is…
1.Explanatory
- A theory explains something
Ex. Germ theory explains that
microbes can make us sick.
In science a theory is…
2. Predictable
- A theory can accurately guess what
will occur in an experiment or
observation
Ex. A certain set of symptoms can be
associated with a certain microbe.
In science a theory is…
3. Testable
- A theory can tested by
experiments or observations
- Must be falsifiable
Ex. If we wash our hands, spread of
microorganisms will be reduced.
Germ Theory
Yes, it’s a theory!
Theory of Evolution
Using our three criteria for a
theory, let’s see if evolution
is a theory.
In science a theory is…
1.Explanatory
- It explains something
Evolution explains how life
changes over time.
In science a theory is…
2. Predictable
- You can accurately guess what
will occur in an experiment or an
observation
Evolution predicts how species will
change over time.
Example: Fossil Record
• The theory of evolution predicts more
complex fossils will be younger than
more primitive fossils.
In science a theory is…
3. Testable
- You can create experiments to
test your hypotheses
- Must be falsifiable
Example: Diane Dodd Experiment
Never say:
Evolution is just a theory.
All of these are theories:
• Theory of Relativity
• Big Bang Theory
• Theory of Plate Tectonics
• Particle Theory
• Quantum Theory
Evolution
What is evolution?
• The scientific theory
that describes
changes in species
over time and their
shared ancestry.
* Evolution does not
explain the origins of
life, science has yet to
discover that.
Evolution is the unifying
theory of biology! It can
be applied to all fields of
biology.
Influences on Evolution
Species change over time (evolution)
AND
The Earth changes over time
(environmental changes)
How does the environment influence
evolution?
Influences on Evolution
• DNA is the blueprint for life
• How does DNA influence evolution?
Mutations
The source of
genetic variation
The Effects of Mutations
Types of Mutations
• Harmful Mutations:
–More common than beneficial
mutations
–Selected against, and have no
influence on populations
–Eg: ???
The Effects of Mutations
Types of Mutations
• Beneficial Mutations:
–Relatively rare
–Favoured by natural selection
–Tend to accumulate in populations
over time
–Eg: opposable thumbs for gripping
The Effects of Mutations
Types of Mutations
• Neutral Mutations:
- Provide no benefit
- or harm to the
- individual
- Will not be selected upon if neither
beneficial or harmful
Mutation Rates
• It is estimated that with such a large genome,
each human may average several mutations
• With well over seven billion people
worldwide, that’s a lot of genetic variability
Influences on Evolution
Selective Breeding
- Humans have domesticated many
organisms (plants and animals)
- Domestication occurs
through artificial
selection
Selective Breeding
Artificial selection – directed breeding
in which individuals that exhibit a
particular trait are chosen as parents
of the next generation
Wild Sea Cabbage
Domestication
Limitations of Selective
Breeding
- Artificial selection can
only influence the
genes present in the
organism
- It cannot create
mutations
- Horticulturalists would
love to create a true
blue rose, but until the
mutation occurs they
cannot breed it
themselves
Genetically Modified “Blue” Rose
Questions
• In textbook:
• PG. 287 #1,3,9
• PG. 317 #28