Function not purpose
The purpose of a hammer is to pound nails. One function of a hand is to hold a hammer.
Designed tools have purposes. Structures and behaviors of living things have functions.
This is an important distinction in the science classroom.
Evidence not proof
We often hear news stories in which the narrator refers to having enough proof.
This is an example of confusing the terms, proof and evidence. In addition, the
term, proof, is used in geometry and in courts of law, but does not belong in science.
Scientists gather evidence to support or falsify hypotheses. Hypotheses and theories may be well
supported by evidence, but never proven.
Primitive and advanced
The average person might see an opossum as more primitive than a cat. Life forms that are more
highly specialized tend to be viewed as more advanced. However, even though opossums retain
some conspicuous ancestral features, they are well adapted to their omnivorous habit and are
every bit as successful and modern as cats. Saber-toothed cats were even more narrowly adapted
than present-day cats and a change in their environment put them on the fast track to extinction.
Theory vs. hypothesis
A theory is an explanation. The validity of a theory rests upon its ability to explain phenomena.
Theories may be supported, rejected, or modified, based on new evidence. Gravitational theory, for
example, attempts to explain the nature of gravity. Cell theory explains the workings of cells.
Evolutionary theory explains the history of life on Earth.
A hypothesis is a testable idea. Scientists do not set out to prove hypotheses,
but to test them. Often multiple hypotheses are posed to explain phenomena and the goal of research
is to eliminate the incorrect ones. Hypotheses come and go by the thousands, but theories often
remain to be tested and modified for decades or centuries. In science, theories are never hunches
or guesses and to describe evolution as just a theory is inappropriate.
Believe or accept
Do you believe in evolution? is a question often asked of biology teachers by their
puzzled students. The answer is, No, I accept the fact that the Earth is very old and life has
changed over billions of years because that is what the evidence tells us. Science is not
about beliefit is about making inferences based on evidence.