Scientific Reasoning…A primer

Though reasoning is a critical component in science it is not often given much attention in undergraduate curricula so I would like to briefly identify some important concepts…

Rodin. “The Thinker”

Some Concepts…

Deterministic/Stochastic Processes Causation vs Correlation Inductive vs Deductive Reasoning Mutually-exclusive and exhaustive Reductionism and Holism Necessity and Sufficiency Hypothesis testing-falsifiable

hypothesis

Deterministic/Stochastic Processes A Deterministic process is one that is a function

of it’s initial state. Trivial example -the time shown on a given watch at

9:00am tomorrow depends on it’s setting today. Biological example -the size of peas produced in

offspring are determined by the genes of the parents.

A Stochastic process is one that is random in outcome (does not depend on initial state).

Trivial example -the outcome of the roll of two dice is random (all possibilities are equally likely.

Biological example -the inheritance of an X chromosome by a son is random (he can inherit either of the two sex chromosomes with equal probability).

Causation vs Correlation

Many scientific studies imply a causative results from correlation results but…

Correlations only suggest associations—they do not indicate causation.

Can use correlations to formulate hypotheses which can be tested experimentally to demonstrate causation.

Inductive vs Deductive Reasoning Deduction-proceeding from the general to

the specific. Trivial example - because of Newton’s law of gravity,

when I kick a ball in the air it will come down. Biological example -the inheritance of an X

chromosome by a son is random (he can inherit either of the two sex chromosomes with equal probability).

Induction-proceeding from the specific to the general.

Trivial example -The ball I kicked in the air fell down so the next ball I kick will also fall down

Biological example – The first four offspring had red hair so the fifth child will have red hair.

Mutually-exclusive and exhaustive experimental outcomes

a set of experimental outcomes is said to be mutually exclusive if they do not intersect and are exhaustive if the sum of the set accounts for all possibilities.

Trivial example – the precipitation today will either be clear, rain or hail. (are mutually exclusive but not exhaustive (since snow was omitted…))

Biological example – in a dihybrid cross, the 9:3:3:1 ratio of possible offspring represents all possible results (are both mutually exclusive and exhaustive...)

Reductionism and Holism

Reductionism - the view that complex processes can be can explained by simple, fundamental rules

Biological example - the lac operon (and gene regulation in general can be described by simple models.

Holism - the view that processes are complex and not amenable to simplification

Biological example – organization with in ecosystems.

Necessity and Sufficiency

If a factor is required for a given phenomenon, it is said to be necessary.

If that factor alone is required it is said to be sufficient.

Example – hydrogen bonding between DNA strands is both necessary and sufficient for annealing of complementary DNA strands

Hypothesis testing - The falsifiable hypothesis

Karl Popper – developed the notion that hypotheses survive attempts at falsification and thus become theories

What make a good hypothesis? Must be testable Simple (unqualified…) challenge established paradigms be broadly applicable (and useful…) make specific testable predictions

Examples of Good Hypotheses…

Non-Biological – The stock market will crash tomorrow. (simple, broad, challenges conventional thought, makes a specific prediction and is testable.)

Biological - Bacterial infections are responsible for most ulcers in humans. (how does this fit with our stated criterion?)

Famous Scientific Philosophers…

-developed the idea that progression in science occurs through revolution

Thomas Kuhn1922-1996

-founded “objectivism” essentially a form of extreme rationalism

Ayn Rand1905-1982

-formalized hypothesis testing Karl Popper 1902-1994

-extended Russell’s work on the logic of philosophy

L. Wittgenstein1889-1951

-developed rule of logic applied to science (mainly math)

Bert Russell 1872-1970

-science is dependent on the observer not just the objects being studied.

I.Kant1724-1804

-formalized scientific inquiryPlato 429-347 BC

Further Reading…

Popper, Karl. The Logic of Scientific Discovery, Routledge Press, London, (1959).

Thomas Kuhn. The Structure of Scientific Revolutions, University of Chicago Press, Chicago (1962)

The end...