Why Is Biology Different?

It may have occurred to you at one time or another that there are some subtle differences between Biology as a science and Chemistry, Physics, and Mathematics.  Obviously, the main difference is that Biology deals with living organisms, but the ramifications of this fact go beyond just the subject matter, because it also affects the nature of the scientific methods employed by biologists.

The evolutionary biologist Ernst Mayr has written extensively on the philosophical implications of evolutionary biology and has discussed (Mayr, 1982) what he sees as the fundamental points that should be incorporated into a philosophy for the biological sciences.  That these principles have not been recognized more clearly is because, according to Mayr, philosophers of science continue to use the physical sciences (especially Physics) as a model for all of the sciences.  The points raised by Mayr are summarized in the table below and are as follows:

Understanding Organisms: One approach to understanding a phenomenon is to reduce it to its fundamental aspects, and, by understanding each component, you can gain some appreciation of the overall process.  This approach, often referred to as reductionism, is useful, especially in the physical sciences, where, for example, a knowledge of the behavior of individual atoms allows you to  predict the dynamics of an reaction system.  However, the hierarchical organization of biological systems makes it impossible to understand all aspects of even a single organism by studying each of its components.  Furthermore, there are certain biological processes, like Natural Selection, which cannot be predicted based on only a knowledge of Physics and Chemistry.  In other words, the entire range of material phenomena are to be found in biological systems, whereas  Physics and Chemistry only deal with a subset of these phenomena.

History: There are many disciplines, besides History itself, where unique historical events play a critical role.  Astronomy and Geology, for example, are often concerned with individual historical  events.  In Biology, however, we study not only historical events but also the organisms which have been either directly or indirectly shaped by those events.  A good case in point is the effect of the extinction of the dinosaurs on subsequent mammalian diversification.  This historical aspect of biology is compounded by the fact that the DNA within each organism is in fact an historical record of the ancestor-descendant relationships of that particular individual.
 


Principles that should be included in the formation of a philosophy for the biological sciences.  From Mayr (1982).
 

1. That a full understanding of organisms cannot be secured through the theories of Physics and
    Chemistry alone.

2. That the historical nature of organisms must be fully considered, in particular their possession
    of  an historically acquired genetic program.

3. That individuals at most hierarchical levels, from the cell up, are unique and form populations,
     the variance of which is one of their major characteristics.

4. That there are two biologies, functional biology, which asks proximate questions, and
    evolutionary biology, which asks ultimate questions.

5. That the history of biology has been dominated by the establishment of concepts and by their
     maturation, modification, and - occasionally - their rejection.

6. That the patterned complexity of living systems is hierarchically organized and that higher
     levels  in the hierarchy are characterized by the emergence of novelties.

7. That observation and comparison are methods in biological research that are fully as scientific
     and heuristic as the experiment.

8. That an insistence on the autonomy of biology does not mean an endorsement of vitalism,
    orthogenesis, or any other theory that is in conflict with the laws of chemistry or physics.
 


Uniqueness: One of the things that enables research in the physical sciences to be so efficient and precise is the fact that there is so little variability in many of the entities studied.  For example, all atoms of a particular isotope of carbon behave in exactly the same way, and this means that an organic chemist can readily predict the outcome of a particular reaction.  Contrast this situation with that of a biologist, who, regardless of his or her field must deal with the fact that the subjects being investigated are not all the same, but instead differ to some degree because they have different genotypes.  Even studies at the biochemical level must take into account the possible existence of more than one protein variant in a given system.  The variance that is observed in physical systems is treated as either an error in measurement or as the result of some random "noise" factor, but in biological research the observed variance is a reflection of a fundamental aspect of living systems.
 
Two Approaches to Biology:  The tendency to look at some aspects of biology as being somehow less "scientific" than the physical sciences is not restricted to philosophers of science who use the physical sciences as their model; the same attitude can be found within biology because there are two main ways in which biologists can approach their research.  In studying a particular phenomenon, you can ask either proximate or ultimate questions.  The proximate aspects of a phenomenon are usually related to the question "How...?", while the ultimate issues are usually addressed by "Why...?".  For example, it is well known that male frogs call during the mating season in order to attract females.  You could study this phenomenon by describing the vocalization mechanism of the males, the frequencies of the sounds produced, and the auditory apparatus of the females.  Each of these is basically a functional, physiological question, but there is the other approach to the same question which is to determine the significance of what is happening.  One simple explanation  is that these calls are the only way in which the sexes can find each other in the dark.  However, an increasing amount of research shows that these calls are critical to the process of mate selection and subsequent mating success (e. g., Ryan, 1990).  Addressing this issue requires that we determine the evolutionary processes associated with the mating system - the fitness consequences of mating with a particular male, the correlation, if any, between male calling frequency and fitness, etc.   Obviously, studying this aspect of the phenomenon is not as clear cut as the physiological questions, but it is still a legitimate scientific inquiry.  In fact, those who deal with proximate questions in biology often find that the more they learn about their systems, the more they must concern themselves with the ultimate, evolutionary issues.

Concepts in Biology:  The model of the scientific method that is derived from the physical sciences leaves one with the impression that the goal of science is to generate "laws" (e. g., the statements of Newton and Kepler on general and planetary motion, respectively).  Laws in this sense are statements of fact that have been demonstrated to fit all known cases.  Biologists have occasionally suffered from a desire to emulate the physical sciences by establishing laws (e. g., Ernst Haeckel's Biogenetic Law - "Ontogeny recapitulates Phylogeny"), but the historical component and intrinsic variability of biological systems make such universal statements impossible.  Biological science advances by developing general concepts which are used to guide our approach to particular phenomena.  Natural Selection is an example of a concept, and, while some have discussed it from the perspective of a law (Reed, 1981), it is merely a formal generalization about the interactions among the environment, organisms, and the genotypes of those organisms in terms of the impact of these interactions on genotypic frequencies.  The formal generalizations of biology always include exceptions that "prove the rule" and result in the modification and refinement of the concepts over time.

Hierarchy:  Students in Biology are well acquainted with the listing of the biological hierarchy that runs from molecules and cells to ecosystems and the biosphere, but few ever stop to think about the ramifications of this hierarchy for the study of biological systems.  The existence of this structure in biological systems means that we must deal with the fact of emergent properties at each level.  The concept of emergence is the idea that the entire system may exhibit properties that are not deducible from a knowledge of the individual components of the system.  This idea is often summarized by the phrase "the whole is greater than the sum of the parts".  The existence of emergent properties in living systems is what limits the usefulness of the reductionist approach to biology.  The recognition of the hierarchical structure of life on this planet has caused some to suggest that major areas of biological investigation should operate formally with this structure in mind (e. g., Eldredge, 1985; O'Neill, et al., 1986).

Observation and Comparison:  The introductory textbook description of the scientific method has scientists operating by making observations, formulating hypotheses, and conducting experiments to test their hypotheses.  This is an accurate description of how to study common, contemporary phenomena, but how, for example, do you go about scientifically studying the extinction of the dinosaurs?  The notion of the laboratory experiment as the scientific method is so ingrained that even biologists who study proximate questions in existing organisms tend to discount the efforts of those who conduct evolutionary and/or ecological research.  However, evolutionary biologists can - and do - formulate hypotheses, but only some of these hypotheses are testable through controlled laboratory or field experiments.  In many instances, evolutionary hypotheses can be tested only by comparing populations or species under different sets of conditions, or, in the case of past events, looking for evidence related to corollaries of the main hypothesis.  For example, if an asteroid impact caused the extinction of the dinosaurs at the end of the Cretaceous (Alvarez, et al., 1980), then there should be several geological and paleontological lines of evidence which would support this scenario.

Biology as an Autonomous Science:  Whenever people argue that there is an intrinsic difference between living and non-living systems, they leave themselves open to the charge that they are advocating either vitalism or orthogenesis.  Vitalism is the discredited notion that what makes living systems different is their possession of some "vital force" that when removed from the system just leaves you with a mass of organic molecules.  This concept was most recently popularized in the 20th century by the French philosopher Henri Bergson.  Orthogenesis is a related concept which holds that the evolutionary process is somehow goal-directed to produce progressively higher levels of perfection and complexity.  The application of this concept to evolution has a history that stretches from Lamarck to the theological writings of Teilhard de Chardin.  As you have seen, there is no need to postulate the existence of some metaphysical force to explain the difference between living and non-living systems.  The reason why Biology differs from the physical sciences is because of the characteristics of living systems which are, among others: (1) the importance of history in organic evolution; (2) the possession of a structured, inheritable genetic program; (3) the hierarchical structure of living systems, and the existence of emergent properties at almost every level; (4) the fact that certain processes (e. g., Natural Selection) only occur in living systems.