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29 Nisan 2012 Pazar
DETERMINISM, REDUCTIONISM, AND GENETICS
One of the fundamental aspects of most Western science is reductionism. The idea,
attributed generally to influential thinkers such as Descartes and Francis Bacon,
derives from our notions of empirical experimental design that the phenomena of
nature can—indeed, perhaps should—be studied and understood part by part,
ultimately all the way down to the most fundamental parts. This does not mean
that each part acts independently, nor that we necessarily ever will understand all
aspects of a trait.
But it does assume that in principle we can come to a fundamental
understanding of a phenomenon by isolating and analyzing its component
effects. Just the way we disassemble a machine into its parts (discussed earlier).
The ultimate belief of reductionism is that the universe is (only) a space filled
with matter and energy. If this view is true, then everything can in principle be
“reduced” to, that is, ultimately explained in terms of (only), molecular and energetic
phenomena. Biological phenomena, too, will ultimately be understood best in
terms of the molecular biology of genes, the “atoms” of biological information (in
some ways, biochemists would extend this even further down, of course). In this
spirit, geneticists seek to study each trait in terms of genes, as separable causal elements.
The objective is to explain a phenotype in terms of the effects of the individual
genes that affect it—just the way we reassemble a machine from its parts.
Reductionism in biology works at various levels. Functional anatomists attempt
to reduce traits like locomotion to the contribution of individual bones and muscles.
To a psychologist, learning may be comprised of recognition, memory storage,
memory recall, units of meaning, and ultimately to neurons and neurotransmitters.
To an ecologist, an ecosystem consists of predators, prey, a food chain, etc.
Each biologist chooses his/her level of reduction. Some may choose to look only
at the role of frogs in the biodiversity of a swamp without feeling compelled to try
to explain the croaking of the frog in terms of its genes. Some wish to go farther
and to “reduce” the croaking to hormone receptors, neuronal pathways, and the like.
A biochemist may see this all as a problem in ligand-receptor binding, signal transduction,
and gene regulation by action potentials of auditory hair cells.
Some biologists, although acknowledging that one can account for a frog in terms
of chemicals, believe that reductionism cannot adequately explain the croaking.
From this point of view, the phenomenon is an emergent one, that must be understood
at its own level of organization. Field biologists may not even care to try to
understand a bullfrog’s croak and his mate’s response in terms of DNA sequence
data or hormone kinetics, a level of accounting in which they have no interest—any
more than you might think the words you are reading could be understood by analyzing
the chemistry of their ink and paper.
To some reductionists, higher-level studies barely count as important science, as
they are too superficial.A common reason given is that we are not as good at making
“operational” the study of complexity as we are at reductionist, experimental
methods. The latter have a long history, and the triumphs of modern science and
technology are the fruit. This view holds that higher-order phenomena are not fundamental
and that eventually we will be able to predict “emergent” biological—or
even cultural—traits by analyzing their components (e.g.,Wilson 1998). Science does
not allow nonmaterial causation, so how can an understanding of any phenomenon
of nature not follow from an adequate understanding of its parts?
A reductionist perspective does not assert that causation is always one-to-one,
but only that if we know all the actors, we will explain the play. An illustration of
the issues involves gene action. Geneticists have long recognized that genes are
often pleiotropic, that is, have many functions. Similarly, different genotypes can
be found in individuals with the same phenotype. The genotype-to-phenotype
relationship is often many-to-many in nature. Even if each component can be
characterized in molecular terms, the overall effect of a gene on an organism, or of
natural selection on a gene, may depend on the set of interacting constraints. We
may not be able to predict the trait from any one of its components, but we should
be able to do so from the set. An important question is when or how well we can
ascertain or even define what that set is.
Arguments about reductionism are not new, and they are probably not resolvable,
but the points are important in this book, whose aim is to understand the role
of genes in how organisms manage their lives. But what it means to “understand”
a phenomenon depends to a great extent on the question being asked.
Source: Genetics and the Logic of Evolution - Kenneth M. Weiss