Nothing in Biology Makes Sense
Except in the Light of Evolution
- Theodosius Dobzhansky
What is Science?
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Nature exists separate from our mind
Our perceptions & instruments can perceive features of Nature
Natural phenomena have natural causes
Natural ‘laws’ operate the same everywhere and for all time (past &
future)
Valid observations are replicable by independent observers
Inferences about observations are provisional, and may change as new
observations are made or new models of natural phenomena are
proposed
Scientists hold values, and make professional decisions based on those
values, but observations are to be reported as objectively as humanly
possible
An observation is to be publicly reported, thoroughly enough that
anyone can accurately attempt to replicate it, and evaluate the
reasonableness of inferences made based on it – Peer Review is
intended to assure this
Biology is the Science of Life
What characterizes a Life form?
• Complex, organized structures of (primarily) carbon-based
molecules
• Converts materials and energy from the environment to
other forms
• Actively maintains its complex structures and internal
environment
• Grows
• Responds to environmental stimuli
• Reproduces accurate copies of itself
• Evolves (changes), usually in response to changing
environmental conditions
Hierarchy of Biological Organization
Increasing Complexity
Atoms
Molecules
Organelles
Cells
Tissues
Organs
Organ Systems
Individuals
Populations
Species
Communities or Higher Taxa
Ecosystem or Higher Taxa
Biosphere
Increasing Complexity
Hierarchy of Biological Organization
Issues in Biology
How do we integrate multiple levels of explanation?
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Hierarchy
Reductionism
Emergent Properties
Scale
Proximate Causation: How Questions
Ultimate Causation: Why Questions
Biological
Phenomenon
Hypothesis
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Prediction 1
Prediction 3
Prediction 2
Hypothesis
B
Prediction 1
Prediction 3
Prediction 2
How Do We Test Theories ?
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Good
:(
Bad
Seek supporting evidence
for one hypothesis.
Test multiple
working hypotheses.
Reject what you can.
Biological
Phenomenon
Hypothesis
A
Prediction 1
Prediction 3
Prediction 2
Hypothesis
B
Prediction 1
Prediction 3
Prediction 2
Methods of Inquiry
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Observational Data
Comparative Data
Theoretical Models
Experiments
Offspring Number
Observational Data
Helper Number
Black-backed jackal
Comparative Data
Homology
Resemblances due to common evolutionary history
Convergence
Independently derived similarities, usually
Due to living in a similar environment
Convergence?
Homology?
Homology
Convergence
Theoretical Models
size
size
• Clarify thinking
• Graphical Models
• Computer Simulations • Identify constraints
• Analytical (Math)
• Make testable
Models
predictions (forecast)
Experiments
• Natural – natural perturbation
• Manipulative – perturbation
purposefully caused by scientist
– Press
• Continuous perturbation
– Pulse
• One – time perturbation
What Makes an Experiment
Good?
Internal Validity
- is the experiment well designed?
External Validity
- does the experiment answer the general question?
In Vitro > Cell/Tissue Culture > Animal Model > Human Trial
Laboratory > Mesocosm > Field
Requirements for a Good
Experiment
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Validate & Calibrate
Control
Replicate
Randomize
Intersperse
• Validate & Calibrate
– Show that technique really does provide data you want (e.g.
test against another, valid technique)
– Show that technique continues to work (nothing that can
change has changed)… includes observer accuracy!
• Control
– Eliminate confounding factors by creating uniformity among
samples, statistically removing predictable extraneous effects
– Provide a comparison that only differs in the factor(s) of
interest
– Reduce observer bias by ‘blind’ scoring protocols
• Replicate
– Reduce risk that results are due to ‘chance’ variation by doing
multiple, independent replications of each treatment type
• Randomize
– To prevent results being due to differences in extraneous
factors among subjects (or treatment replicates), make
assignment of treatment type as random as possible
• Intersperse
– To prevent results being due to differences in the time or
spatial position of treatment-types, intersperse as evenly as
possible the preparation and position of replicates of each
treatment-type
Pesticide Toxicology Test
A field trial
= apply water only
= dilute application
= recommended application
= heavy application