Emerging Diseases

Lecture 2: The Scientific Method

2.1: Overview2.2: Scientific Method2.3: Scientific Theories

2.1: Overview-Science as a Process

• “Scientific Method”• Common sense way of asking

questions and getting answers about nature

• Organized and logical but also intuitive and personal

• Science is a part of human society and culture

• Science is a social activity

2.2: Scientific Method:

I

• It starts with information or observations.

• The information generates a question.

• The question suggests a possible answer or answers.

• The possible answer is called a hypothesis.

Scientific Method •The hypothesis has to be checked out or “tested”.•In the natural sciences (biology, chemistry, physics) the test is often made via an experiment.•An experiment is a test of a hypothesis carried out under controlled conditions.

Scientific Method • The results of the experiment either support

the hypothesis or do not support the hypothesis.

• Of course scientists usually prefer it when the results support the hypothesis.

• But either way, the results lead to new questions and experiments.

The Scientific Method is Cyclical

Questions generate results: results generate questions.

Scientific Knowledge is Powerful

• Because it is based on real-world experiments• And it can always be re-tested and re-checked

But Scientific Knowledge is Tentative

• Because there are always more questions• Scientific knowledge can be falsified, modified,

shown to be limited or even discarded.

2.3: The Scientific Method Builds up to Theories

• A really important hypothesis that has been tested and supported many times is called a theory (sometimes a law).

• A theory has stood up to all tests for so long that the scientific community does not really question it any longer.

• Even so, someday, somewhere some other scientist might show that the theory is not always correct.

A scientific theory is different from a

theory in the media!!!!!!!!!!

A scientific theory is backed up by a large body of hard evidence.

A scientific theory is generally accepted by the community.

News anchors, talking heads, radio and TV personalities can make up anything they want and call it a “theory”.

They don’t need evidence, discussion or consensus!

The End of a Theory

• Eventually a theory gets old and becomes less useful.

• New evidence accumulates and the old theory has a hard time explaining it.

• Time for a new theory or a modified theory.• The switchover is called a paradigm shift.• An example is the shift from humoral medicine

to the Germ Theory.

Two Important Theories in Biology

The Cell Theory (early 1800s)All living organisms are made up of one or more

cells.

The Theory of Evolution (late 1800s)Through preferential reproduction of some

members, species change over time in response to external changes such as environmental

change.

Modern Understanding of the Cell Theory

There are three types of cells and thus three main groups of organisms. These groups are

called domains.

ArchaeaBacteria (aka Eubacteria)

Eukaryotes

Evidence for Three Domains

• Lots of biochemical evidence• The best evidence comes from studies of

genes. The genes fall into 3 main groups based on the code that the genes contain.

• Evidence first provided by Carl Woese.