In many fields of biology, new concepts contribute as much as new discoveries to progress. There are many theories in which scientists have great confidence. However, the processes of science are self-correcting and new evidence may challenge cherished ideas. Uncertainty in science is an inescapable consequence of the paradigm or way of proceeding in the culture of science. You should understand not only why there is some uncertainty in science but also how scientists use tentative language to honestly express their degree of confidence in a theory.
Science is based strongly on the search for principles.
There are common principles, but these are rarely universal laws, in contrast to the laws of physics and chemistry. Scientists use analogy to develop hypotheses about seemingly similar situations and then must test the new hypotheses. Analogy is a very useful form of inductive reasoning, but the strength of the analogy depends on the strength of the similarity between the organisms compared.