Science as we know it is the product of developments in the
17th and 18th centuries. What was conceived as science is indicated by the
names Galileo, Kepler, Newton, Descartes, and Leibniz. It was the glorious rise
of the physical sciences advancing from triumph to triumph. It was physics what
people meant when they talked about science, biology was never included. The
science of biology was a creation of the l9th century. Of course, there were
branches of medicine such as anatomy, physiology, and embryology that we now
include in biology but they were concerned with healing and were not considered
to be the part of a separate science of biology. At the same time there was
also a flourishing pursuit of natural history under the label of Natural
Theology. A genuine biology remained dormant until the 19th century.
It took more than two hundred years and the occurrence of
three different sets of events before a genuine science of biology originated.
One can assign these events to three different sets: (A) the refutation of
certain erroneous principles, (B) the demonstration that certain basic
principles of physics cannot be applied to biology, and (C) the realization of
the uniqueness of certain basic principles of biology that are not found in the
inanimate world. Let us now review these three sets of events.
A: The refutation of certain erroneous basic assumptions.
Under this heading I deal with the support for certain basic
ontological principles which later were shown to be erroneous. Biology could
not be recognized as a science of the same rank as physics as long as most
biologists accepted certain basic explanatory principles not supported by the
laws of the physical sciences and eventually found to be invalid. The two major
principles here involved are vitalism and a belief in cosmic teleology. As soon
as it had been demonstrated that these two principles are invalid and, more
broadly, that none of the phenomena of the living world are in conflict with
the natural laws of the physicalists, there was no longer any reason for not
recognizing biology as a legitimate autonomous science, equivalent to physics.
Vitalism
The nature of life, the property of being living, has always
been a puzzle for the philosophers. Descartes tried to solve it by simply
ignoring it. An organism is really nothing but a machine, he said. And other
philosophers, particularly such with a background in mathematics, logic,
physics, and chemistry, tended to follow him and operated as if there was no
difference between living and inanimate matter. But this did not satisfy most
naturalists. They were convinced that in a living organism certain forces are
active which do not exist in inanimate nature. They concluded that just as the
motion of planets, suns, and stars, is controlled by an occult, invisible force
called by Newton gravitation, analogously the movements and other
manifestations of life in organisms is controlled by an invisible force,
Lebenskraft orvis vitalis. Those who believed in such a force were called
vitalists.
Vitalism was popular from the early 17th century to the
early 20th century. It was a natural reaction to the crass mechanism of
Descartes. Henri Bergson and Hans Driesch were prominent vitalists in the early
20th century. The end of vitalism came when it could no longer find any
supporters. Two causes were largely responsible for this, first the failure of
literally thousands of failed experiments conducted to prove the existence of a
Lebenskraft, and secondly, the realization that the new biology, with the
methods of genetics and molecular biology, was able to solve all the problems
for which one traditionally had invoked the Lebenskraft. In other words the
proposal of a Lebenskraft had simply become unnecessary.
It would be ahistorical to ridicule vitalists. When one
reads the writings of one of the leading vitalists like Driesch one is forced
to agree with him that many of the basic problems of biology simply cannot be
solved by a philosophy as that of Descartes, in which the organism is simply
considered a machine. The developmental biologists in particular asked some
very challenging questions. For exarnple, how can a machine regenerate lost
parts, as many kinds of organisms are able to do? How can a machine replicate
itself ? How can two machines fuse into a single one like the fusion of two
gametes when producing a zygote ?
The logic of the critique of the vitalists was impeccable.
But all their efforts to find a scientific answer to all the so-called
vitalistic phenomena were failures. Generations of vitalists labored in vain to
find a scientific explanation for the Lebenskraft until it finally became quite
clear that such a force simply does not exist.
Teleology.
Teleology is the second invalid principle which had to be
eliminated from biology before it qualified as a science equivalent to physics.
Teleology deals with the explanation of natural processes which automatically
seem to lead to a definite end or goal. To explain the development of the
fertilized egg to the adult of a given species Aristotle invoked a fourth
cause, the causa finalis. Eventually one invoked this cause for all phenomena
in the cosmos which led to an end or goal. Kant in his Critique of Judgment had
tried to explain the biological world in terms of Newtonian natural laws but
had been completely unsuccessful in this endeavor. Frustrated he ascribed all
Zweckmässigkeit as being due to teleology. This was, of course, no solution. A
widely-supported school of evolutionists, for instance the so-called
orthogenesists, invoked teleology to explain all progressive evolutionary
phenomena. They believed that in living nature there is an intrinsic strive
toward perfection. Here belongs also Lamarck's theory of evolution and
orthogenesis had many followers prior to the evolutionary synthesis. Alas, no
evidence for the existence of such a teleological principle could ever be found
and the discoveries of genetics and paleontology eventually totally discredited
cosmic teleology. The distinguished philosopher Quine told me once that he
considered it as Darwin's greatest achievement to have refuted Aristotle's
fourth cause by showing that the attainment of a definite goal in evolution
could be explained by natural selection. There are numerous seemingly
goal-directed processes in nature, particularly in biology, which one now no
longer explains by occult teleological forces but by scientifically supported
chemical-physical factors. I distinguish four groups of such factors which
formerly had been referred to as teleological (Mayr 1992, 1998). The fifth
group of factors, attributed to an intrinsic potential of the cosrnos to cause
goal direction, could never be substantiated. Such cosmic teleology is now
considered not to exist.
What is biology ?
When we investigate this we find that biology actually
consists of two rather different fields, functional biology and historical
biology. Functional biology deals with the physiology of all activities of
living organisms, particularly with all cellular processes, including those of
the genome. These functional processes can be explained by chemistry and
physics.
The other branch of biology is historical biology. A
knowledge of history is not needed for the explanation of a purely functional
process. It is however all-important for the explanation of all aspects of the
living world that involve the dimension of historical time, in other words, as
we now know, all aspects dealing with evolution.
The two fields of biology also differ in the nature of the
most frequently asked questions. To be sure in both fields one asks what?
questions, in order to get the facts needed for further analysis. The most
frequently asked question in functional biology, however, is how?, while in
evolutionary biology it is why? This difference is not complete because in
evolutionary biology one also asks occasionally how? questions, for instance
how do species multiply ? However, as we will see, evolutionary biology has
developed its own methodology, that of historical narratives, to obtain its
answers, particularly in cases where experiments are inappropriate.
In order to truly appreciate the autonomy of biology one
must know the remarkable difference between these two branches of biology.
Indeed some of the most decisive differences between the physical sciences and
biology are true for only one of these branches, for evolutionary biology.
The emergence of modern biology.
The two hundred year period, from ca. 1730 to 1930,
witnessed a radical change in the conceptual framework of biology. It included
the period from 1828 to 1866 during which both branches of modern biology,
functional and evolutionary biology, were established, which resulted in the
eventual refutation of vitalism and cosmic teleology. Yet biology was still
largely ignored by the philosophers of science from Carnap, Hempel, Nagel,
Popper, to Kuhn. The biologists, even though they now rejected vitalism and
cosmic teleology, were unhappy with a purely mechanistic philosophy of biology.
But all endeavors to escape from this dilemma, such as for example the writings
of Jonas, Portmann, Uexküll, and several others, invariably invoked some
non-mechanical forces. It was not until almost the middle of the 20th century
until it became evident that a solution could not be found by a philosopher who
did not have a background in biology. At the same time it became equally clear
that, however the solution would be, it had to be completely compatible with the
natural laws. No solution was acceptable that would invoke any occult forces.
But how could such a solution be found ?
It turned out that in order to develop an autonomous science
of biology one had to do two further things. First, undertake a critical analysis
of the conceptual framework of the physical sciences. This revealed that some
of the basic principles of the physical sciences are simply not applicable to
biology. They had to be eliminated and replaced by principles pertinent to
biology. And secondly, it was necessary to investigate whether biology is based
among others on certain additional principles that are inapplicable to
inanimate matter. This required a restructuring of the conceptual world of
science that was far more fundamental than anyone had imagined at that time. lt
became apparent that the publication in 1859 of Darwin's Origin of Species was
really the beginning of an intellectual revolution that ultimately resulted in
the establishment of the autonomy of biology.
B. Physicalist ideas not applicable to biology.
Darwin's ideas were particularly important in the discovery
that a number of basic concepts of the physical sciences, which up to the
middle of the 19th century were also widely held by most biologists, are not
applicable to biology. I will now discuss four of these basic physicalist
concepts for which it had to be demonstrated that they are not applicable to
biology, before it was realized how different biology is from the physical
sciences.
1. Essentialism.
From the Pythagoreans and Plato on the traditional concept
of the diversity of the world was that it consisted of a limited number of
sharply delimited and unchanging eide or essences. This viewpoint was called
typology or essentialism. The seemingly endless variety of phenomena, it was
said, actually consisted of a limited number of natural kinds (essences or
types) each forming a class. The members of each class were thought to be
identical, constant, and sharply separated from the members of any other
essence. Therefore, variation was nonessential and accidental. The
essentialists illustrated this concept by the example of the triangle. All
triangles have the same fundamental characteristics and are sharply delimited
against quadrangles or any other geometric figure. An intermediate between a
triangle and a quadrangle is inconceivable.
Typological thinking, therefore, is unable to accommodate
variation and has given rise to a misleading conception of human races.
Caucasians, Africans, Asians, or Inuits are types for a typologist that
conspicuously differ from other human ethnic groups and are sharply separated
from them. This mode of thinking leads to racism. Darwin completely rejected
typological thinking and used instead an entirely different concept, now called
population thinking (see below).
2. Determinism.
One of the consequences of the acceptance of deterministic
Newtonian laws was that it left no room for variation or chance events. The
famous French mathematician and physicist Laplade boasted that a complete
knowledge of the current world and all its processes would enable him to
predict the future to infinity. Even the physicists soon discovered the
occurrence of enough randomness and contingencies to refute the validity of
Laplace's boast. The refutation of strict determinism and of the possibility of
absolute prediction freed the way for the study of variation and of chance
phenomena, so important in biology.
3. Reductionism.
Most physicalists were reductionists. They claimed that the
problem of the explanation of a system was resolved in principle as soon as the
system had been reduced to its smallest components. As soon as one had
completed the inventory of these components and had determined thc function of
each one of them, they claimed it would be an easy task to explain also
everything observed at the higher levels of organization. This claim was
vigorously objected to by biologists already more than one hundred years ago.
Darwin's friend T. H. Huxley asked the reductionists why the reduction of water
(H2O) to hydrogen gas and oxygen gas did not explain the nature of water ? What
the reductionists confused was reduction and analysis. Of course we learn a
great deal about any complex system by analyzing it. Indeed analysis is a most
important and heuristic method in all branches of science, including biology.
But first of all, in many cases of analysis, one does not have to go anywhere
near the smallest parts (electrons, protons, etc...). Furthermore, and this is
what the reductionists usually overlooked, in order to understand a system one
needs to know not only the properties of its components but also the nature of
the interactions among these components. And it is precisely these interactions
that are so important in living systems. Their study is the objective of the
holists (see below).
4. Laws.
All theories in the physical sciences are based on natural
laws. Normally they have no exceptions which led Popper to the claim that any
exception to a theory amounted to its falsification. Indeed, on the whole,
properly articulated laws are the basis of the theory structure of the physical
sciences. But is this also true for biology ? This has been seriously
questioned by a number of philosophers (Smart 1963, Beatty 1995) and only few
biological theories are based on laws. They are usually rather based on
concepts, as we shall presently see.
The inapplicability of these four principles that are so
basic in the physical sciences, has contributed a great deal to the insight
that biology is not the same as physics. To get rid of these erroneous ideas
was the first but perhaps hardest step in developing a sound philosophy of
biology.
C. Autonomous characteristics of biology.
The last step in the development of the autonomy of biology
was the discovery of a number of biology-specific concepts or principles. One
is the concept of evolution. To be sure even before Darwin geologists knew
about changes on the Earth's surface and cosmologists were aware of the
probability of changes in the universe, particularly in the solar system.
However, the world was seen as something quite constant, something that had not
changed since the day of Creation. This view totally changed after the middle
of the 19th century when science became aware of the comprehensiveness of the
evolution ofthe living world.
The adoption of the concept of the biopopulation is
responsible for what now seems probably the most fundamental difference between
the inanimate and the living world. The inanimate world consists of Platonian
classes, essences, types, with the members of each class being identical, and
with the seeming variation being "accidental" and therefore
irrelevant. In a biopopulation, by contrast, every individual is unique, while
the statistical mean value of a population is an abstraction. No two of the six
billion humans are the same. Populations as a whole do not differ by their
essences but only by mean statistical values. The properties of populations
change from generation to generation in a gradual manner. To think of the
living world as a set of forever variable populations grading into each other
from generation to generation, results in a concept of the world that is
totally different from that of a typologist. The Newtonian framework of
unalterable laws predisposes a physicist to be a typologist, seemingly almost
as if by necessity. Darwin introduced population thinking into biology rather
casually, and it took a long time before it was being realized that this is an
entirely different concept from the typological thinking traditional in the
physical sciences (Mayr 1959).
Population thinking and populations are not laws but
concepts. It is one of the most fundamental differences between biology and the
so-called exact sciences that in biology theories are usually based on concepts
while in the physical sciences they are based on natural laws. Examples of
concepts that became important bases of theories in various branches of biology
are territory, female choice, sexual selection, resource, and geographic
isolation. And even though, through appropriate rewording, some of these
concepts can be phrased as laws, they are something entirely different from the
Newtonian natural laws.
All biological processes differ in one respect fundamentally
from all processes in the inanimate world; they are subject to dual causation.
In contrast to purely physical processes these biological ones are controlled
not only by natural laws but also by genctic programs. This duality fully
provides a clear demarcation between inanimate and living processes.
The dual causality, however, which is perhaps the most
important characteristic of biology by which it differs indubitably from the
physical sciences, is a property of both areas of biology. When I speak of dual
causality I am of course not referring to Descartes' distinction of body and
soul but rather to the remarkable fact that all living processes obey two
causalities. One of them are the natural laws which, together with chance,
control completely everything that happens in the world of the exact sciences.
The other causality consists of the genetic programs which characterize the
living world so uniquely. There is not a single phenomenon or a single process
in the living world which is not controlled by a genetic program contained in
the genome. There is not a single activity of any organism that is not
controlled by such a program. There is nothing comparable in the inanimate
world. Dual causation, however, is not the only unique property of biology to
support the thesis of the autonomy of biology. Indeed it is reinforced by some
six or seven additional concepts. I will now discuss some of these.
The most novel and most important concept introduced by
Darwin was perhaps that of natural selection. Natural selection is a process
that is both so simple and so convincing, that it is almost a puzzle why after
1858 it took almost 80 years before it was universally adopted by
evolutionists. To be sure, the process has been somewhat modified in the course
of years. It is rather a shock for some biologists to learn that natural
selection, taken strictly, is not a selection process at all, but rather a
process of elimination. It is the least well adapted individuals that are eliminated
in every generation, and those that are better adapted have a greater chance to
survive. Also, in recent years, there has been a great deal of argument, what
was more important, variation or selection. For me, there is no argument. The
production of variation and true selection are for me inseparable parts of a
single process. At the first step variation is produced by mutation and
recombination, and at the second step the variants are sorted by selection. Of
course, during sexual selection real selection takes place. Natural selection
is the driving force of organic evolution and represents a process quite
unknown in inanimate nature.
This process enabled Darwin to explain the
"design" so important in the arguments of the natural theologians.
The fact that all organisms are seemingly so perfectly adapted to each other
and to their environment was attributed by the natural theologians to God's
perfect design. Darwin however showed that it could be equally well, indeed
even better, explained by natural selection. Before and even after the
publication of the Origin, it was widely postulated that God had given Nature
the capacity to move toward perfection. Indeed many natural processes seem to
move toward a final goal such as the fertilized egg toward the adult stage.
Aristotle had referred to this as the "final cause", later
philosophers had called it teleology.
Evolutionary biology is a historical science. It is very
different from the exact sciences in its conceptual framework and methodology.
It deals, to a large extent, with unique phenomena, such as the extinction of
the dinosaurs, the origin of man, the origin of evolutionary novelties, the
explanation of evolutionary trends and rates, and the explanation of organic
diversity. Evolutionary biology tries to find the answer to why questions.
Experiments are usually inappropriate for obtaining answers to evolutionary
questions. We cannot experiment about the extinction of the dinosaurs or the
origin of mankind. There is, however, a remarkably heuristic method available,
that of historical narratives. Just as in much of theory formation you start
with a conjecture which you thoroughly test for its validity, so in
evolutionary biology you construct a scenario, a historical narrative, which
you test for its explanatory value. Let us take the case of the extinction of
the dinosaurs.
An early conjecture was that they had been the victims of a
devastating viral or bacterial epidemic. For various reasons this narrative was
not very credible. A second scenario suggested that a drastic climatic event
had led to the mass extinction. Geologists however could find no evidence for a
drastic, climatic change. Eventually the physicist Alvarez suggested that the
Earth had been hit by an asteroid which had kicked up such a large amount of
dust that for a short time it had made life on Earth very precarious. The
dinosaurs became extinct but a few probably nocturnal and small mammals had
been lucky to survive. The impact crater of the postulated asteroid was
eventually found near the Yucatan peninsula in Mexico and all other recent
findings since have confirmed the impact theory to such an extent that it is
now quite generally accepted.
The methodology of historical narratives is clearly a
methodology of historical science. Indeed evolutionary biology as a science, is
in many respects more similar to the Geisteswissenschaften than to the exact
sciences. When drawing the borderline between the exact sciences and the
Geisteswissenschaften it would go right through biology and attach functional
biology to the exact sciences while including evolutionary biology with the
Geisteswissenschaften. This, incidentally, shows the weakness of the old
classification of the sciences. That classification was made by philosophers
familiar with the physical sciences and the humanities but completely ignorant
of the existence of biology.
Chance.
The natural laws usually effect a rather deterministic
outcome in the physical sciences. Neither natural nor sexual selection
guarantee such determinism. Indeed the outcome of an evolutionary process is
usually the result of an interaction of numerous incidental factors. Chance is
also rampant in the production of variation. It governs both crossing-over and
the movement of chromosomes in the reduction division. It was curiously this
chance aspect of natural selection for which this theory was most often
criticized. Some of Darwin's contemporaries, for instance the geologist
Sedgwick, declared that invoking chance was unscientific. Actually, it is
precisely the chanciness of variation that is so characteristic of Darwinian
evolution. Even today there is much argument concerning the role of chance in
the evolutionary process. Selection, of course, always has the last word.
Holistic thinking.
Reductionism was the declared philosophy of the
physicalists. Reduce everything to the smallest parts, determine the properties
of these parts, and you have explained the whole system. However, in a
biological system there are so many interactions among the parts, for instance
among genes of the genotype, that a complete knowledge of the properties of the
smallest parts by necessity gives only a partial explanation. Nothing is as
characteristic of biological processes as interactions at all levels, among
genes of the genotype, between genes and tissues, between cells and other
components of the organism, between the organism and its inanimate environment,
and between different organisms. It is precisely this interaction of parts that
gives nature as a whole, or the ecosystem, or the social group, or the organs
of a single organisms, its most pronounced characteristics. To repeat what I
said before, rejecting the philosophy of reductionism is not an attack on
analysis. No complex system can be understood except through careful analysis.
However the interactions of the components must be considered as much as the
properties of the isolated components. And this is what the reductionists had
neglected.
Conclusions.
We are now ready to summarize the results of our study of
the autonomy of biology. Yes, we have concluded, that biology is a science, as
much as chemistry and physics are sciences. However biology is in many respects
a very different science from the so-called exact sciences. Perhaps the most
pronounced difference is that biology, in part, is a historical science. In
this part of biology, evolutionary biology, the method of historical narratives
is the most heuristic approach. Furthermore, biology has as its subject matter
living organisms which in several ways differ quite fundamentally from
inanimate objects. They have, in particular, two characteristics for which
there is no equivalent in the world of the physicist. One is that every process
and every activity is controlled by a double set of causations; the natural
laws and the genetic programs. The natural laws are the same that control the
physical sciences. There is no room in biology for anything, as for instance
vitalism, that would be in conflict with the natural laws. But every living
organism and its parts is also controlled by a second source of causation, the
genetic programs. The absence or presence of genetic programs denotes the sharp
border between the inanimate and the living world. Typological (essentialistic)
thinking is misleading when applied to organisms. What must be used instead is
population thinking which realizes that in a biological population every
individual is unique and differs from all others. The statistical mean value of
a population is merely an abstraction. Dual causality as well as the uniqueness
of every individual of a biopopulation characterize the world of living beings
and are therefore characteristic for biology.
This explains why all endeavors prior to the last fifty
years or so to construct a philosophy of biology within the conceptual
framework of the physical sciences were such a failure. Biology, we now
realize, is indeed largely an autonomous science and a philosophy of biology
must be based on the peculiar characteristics of the living world, recognizing
at the same time that this is not in conflict with a strictly physico-chemical
explanation at the cellular-molecular level.
Literature
[l] E. Mayr: The idea of teleology. J. Hist. Ideas 53, 117
(1992). -
[2] E. Mayr: The multiple meanings of
"Teleological". Hist. Phil. Life Sci. 20, 35 (1998).
[3] J. J. C. Smart: Philosophy and Scientific Realism.
Routledge & Kegan Paul. London 1963.
[4] J. Beatty: The evolutionary contingency thesis. In G.
Wolters, J. Lennox (Hrsg.): Concepts, Theories and Rationality in the
Biological Sciences. University of Pittsburgh Press. Pittsburgh 1995.
adapted for the internet: Peter v. Sengbusch -
b-online@botanik.uni-hamburg.de
Δεν υπάρχουν σχόλια:
Δημοσίευση σχολίου