Evolution: of theories and Theories
Evolution is often dismissed as a mere “theory”; well, it is a theory, or rather, it is a Theory. Confused? You are not alone. The confusion is brought about by the usual lack of a clear distinction in most people between two of the meanings of the word. A “theory” (uncapitalized) is essentially a guess, an opinion, as in “ . . . this is how I think it happened . . .”. As written, if you want to confirm it or dismiss it, you must find evidence to support your interpretation.
A “Theory” (capitalized) in the scientific sense is a model that collects a wide variety of phenomena and integrates them in a coherent framework independently of personal opinions. In this way, a Theory will be capable of explaining additional observations and most importantly, make predictions. The additional observations are used to modify the Theory and in some cases, even change it altogether.
For example, things fall towards the ground. This is an undisputed fact that can be verified by everyone. We describe this as “gravity”, and we can come up with many different explanations of why it happens. In fact, since antiquity, there have been several explanations to account for the fact of gravity, all the way up to Newton and Einstein, yet the proverbial apple does not care about the mechanism; it falls to the ground regardless. Therefore, even though we have a Theory of gravitation, we do not think of gravity as something dependent on our personal opinions. Gravity happens. In this sense, gravitation is both a fact and a Theory.
The same reasoning can be applied to evolution. The undeniable fact is that life on our planet has changed over time. This has been thoroughly documented by many lines of evidence. This is a fact. The Theory of evolution, on the other hand, has historically tried to explain this change over time through a variety of different mechanisms. The best available evidence points at natural selection as the most likely mechanism that accounts for evolutionary change. More recently, some scientists have suggested symbiosis (the close interaction of organisms belonging to different species) as a source for evolutionary innovation. The nature of science, particularly biology, is rarely black or white; there are many shades of gray. For the record, I think that the right answer to account for evolutionary change might just be a combination of natural selection and symbiosis, but this is beside the point. The important thing is that whether symbiosis, natural selection, a combination of the two, or even a yet undiscovered mechanism explains evolution the best (and trust me, scientists have argued and will keep arguing about this), has no bearing on the fact of evolution. Life happened, and has changed over time, period.
For a more thorough (and much better written (:-) exploration of evolution as fact and theory see http://www.stephenjaygould.org/library/gould_fact-and-theory.html)
Another source of confusion is when somebody finds to his utter surprise that science is not written in stone, in other words, that science is provisional. Science is provisional indeed, but some things are more provisional than others. The amount of evidence in favor of a certain interpretation of nature is inversely proportional to how provisional that interpretation is. In other words, the more evidence, the less provisional character. It is a fatal mistake to think that in science all “provisionals” are equivalent.
A final thought in this topic. At the present level of our understanding of the universe, we cannot try to understand it from the proverbial engineer point of view. We are not that smart yet. If only the universe’s reality were that simple! To think that at the present we can always describe the natural world in terms of A goes to B then to C, etc., or to treat all “provisionals” as equals is a gross oversimplification of the nature of things and at the same time a hilarious overestimation of our true capacities.
Why are non-human organisms useful in biomedical research?
The majestic tale of evolution has taught us that all life on earth is related. For example, every single type of organism described to date is built on proteins, lipids and carbohydrates. Bioenergetically, all forms of life use the energy stored in a molecule called adenosine triphosphate (ATP for short). Finally, the genetic information is invariably coded in deoxyribonucleic acid (DNA), a nucleic acid, with contributions by various types of another nucleic acid, ribonucleic acid (RNA).
Prior to the genetic revolution, biology was very successful at figuring out the interrelationships of the many different organisms on earth based on structural or physiological similarities between organisms, taxonomists were able to classify life on our planet. More recently, the availability of genetic information has confirmed and even extended many of these classification schemes, often in unexpected, interesting ways. It is a well-established fact that life as we know it uses the same basic building blocks as described above. This means that the physiology of “lower” organisms closely mimics human physiology (or is it all the way around?). This is why many of the chemicals s that we use to eliminate pests, for example, are harmful to humans and why molecules evolved in say, venomous snakes to allow them to hunt for food, are capable of hurting humans.
Using the same logic, biomedical research using non-human animal models provide scientists with useful insights on disease conditions and on the development of pharmacological agents. Animal research is a controversial topic to say the least; that said, it is undeniable that such research has advanced biomedical sciences in ways that would have been much more difficult or even impossible without it. I will expand these thoughts in my next entries. See you!