The social nature of science is something that we want to stress yet again. While science is often portrayed as an activity carried out by isolated individuals, the image of the mad scientist comes to mind, in fact science is an extremely social activity. It works only because it involves and depends upon an interactive community of scientists who keep each other (in the long run) honest.20 Scientists present their observations, hypotheses, and conclusions in the form of scientific papers, where their relevance and accuracy can be evaluated, more or less dispassionately, by others.
Over the long term, this process leads to an evidence-based consensus. Certain ideas and observations are so well established that they can be reasonably accepted as universally valid, whereas others are extremely unlikely to be true, such as perpetual motion or "intelligent design creationism.” These are ideas that can be safely ignored. As we will see, modern biology is based on a small set of theories: these include the Physicochemical Theory of Life, the Cell Theory, and the Theory of Evolution.21 That said, as scientists we keep our minds open to exceptions and work to understand them. The openness of science means that a single person, taking a new observation or idea seriously, can challenge and change accepted scientific understanding. That is not to say that it is easy to change the way scientists think. Most theories are based on large bodies of evidence and have been confirmed on multiple occasions using multiple methods. It generally turns out that most “revolutionary” observations are either mistaken, misinterpreted, or can be explained within the context of established theories. It is, however, worth keeping in mind that it is not at all clear that all phenomena can be put into a single “theory of everything.” For example, it has certainly proven difficult to reconcile quantum physics with the general theory of relativity.
A final point, mentioned before, is that the sciences are not independent of one another. Ideas about the behaviors of biological systems cannot contradict well established observations and theories in chemistry or physics. If they did, one or the other would have to be modified. For example, there is substantial evidence for the dating of rocks based on the behavior of radioactive isotopes of particular elements. There are also well established patterns of where rock layers of specific ages are found. When we consider the dating of fossils, we use rules and evidence established by geologists. We cannot change the age we assign to a fossil, making it inconsistent with the rocks that surround it, without challenging our understanding of the atomic nature of matter, the quantum mechanical principles involved in isotope stability, or geological mechanisms. A classic example of this situation arose when the physicist William Thompson, also known as Lord Kelvin, (1824-1907) estimated the age of the earth to be between ~20 to 100 million years, based on the rate of heat dissipation of a once molten object, the Earth.22 This was a time-span that seemed too short for a number of geological and evolutionary processes, and greatly troubled Charles Darwin. Somebody was wrong, or better put, their understanding was incomplete. The answer was with the assumptions that Kelvin had made; his calculations ignored the effects of radioactive decay, not surprising since radioactivity had yet to be discovered. The heat released by radioactive decay led to an increase the calculated age of the earth by more than ten to one hundred fold, to ~5 billion years, an age compatible with both evolutionary and geological processes.
20 A good introduction of how science can be perverted is “The undergrowth of Science” by Walter Gatzer.
21 Thinking about the conceptual foundations of the biological sciences: http://www.ncbi.nlm.nih.gov/pubmed/21123685
22 An interesting book on this topic is “Discarded Science: Ideas That Seemed Good at the Time” by Paul Barnett