Scientific ideas are developed through reasoning. Inferences are logical conclusions based on observable facts. Much of what we know from scientific study is based on inferences from data, whether the object of study is a star or an atom. No person has ever seen inside an atom, yet we know, by inference, what is there. Atoms have been disassembled and their components determined. The history of life on Earth has likewise been inferred through multiple lines of evidence.

Scientific claims are based on testing explanations against observations of the natural world and rejecting the ones that fail the test. Scientific explanations are evaluated using evidence from the natural world. That evidence may come from various sources: a controlled lab experiment, a study of anatomy, or recordings of radiation from outer space, to name just a few. Explanations that don’t fit the evidence are rejected or are modified and tested again.

Scientific claims are subject to peer review and replication. Peer review is an integral part of genuine scientific enterprise and goes on continuously in all areas of science. The process of peer review includes examination of other scientists’ data and logic. It attempts to identify alternative explanations, and attempts to replicate observations and experiments.

In the marketplace of ideas, the simplest explanation has the advantage. This principle is referred to as parsimony. Consider these observations:

• A close look at snails, nautiloids, squids, octopuses and cuttlefish reveals the basic similarity of the body form of each (see to the right).
• The shell of a nautilus and its extinct relatives, the ammonites, is very similar to the shell of a snail.
• The tentacles of an octopus, when carefully examined, can be seen to be a modified snail’s foot.
• The stomachs of all members of this group have the same arrangement of parts.

One possible explanation is that these animals have independently acquired equivalent organs through a remarkable series of coincidences, but the most likely explanation is that these animals inherited similar organs through common ancestry. That is parsimony.

There is no such thing as “THE Scientific Method.”

If you go to science fairs or read scientific journals, you may get the impression that science is nothing more than “question-hypothesis-procedure-data-conclusions.”

But this is seldom the way scientists actually do their work. Most scientific thinking, whether done while jogging, in the shower, in a lab, or while excavating a fossil, involves continuous observations, questions, multiple hypotheses, and more observations. It seldom “concludes” and never “proves.”

Putting all of science in the “Scientific Method” box, with its implication of a white-coated scientist and bubbling flasks, misrepresents much of what scientists spend their time doing. In particular, those who are involved in historical sciences work in a very different way — one in which questioning, investigating, and hypothesizing can occur in any order.

Theories are central to scientific thinking.

Theories are overarching explanations that make sense of some aspect of nature, are based on evidence, allow scientists to make valid predictions, and have been tested in many ways. Theories are supported, modified, or replaced as new evidence appears. Theories give scientists frameworks within which to work. Major theories of science, such as the cell theory, gravitational theory, evolutionary theory, and particle theory, are all big ideas within which scientists test specific hypotheses.

The scientific definition of “theory” should not be confused with the way the term is commonly used to mean a guess or a hunch. In science, a theory means much more and is far more well-founded. The “Theory of Evolution” is an evidence-based, internally consistent, well-tested explanation of how the history of life proceeded on Earth — not a hunch. Understanding the role of theory in science is essential to scientists and vital to the informed citizen.