This is a summary of some parts of Alex Rosenberg’s and Daniel McShea’s “Philosophy of Biology.”
The reductionist holds that biological theories, generalizations, and explanations can be reduced to physics. It is not that biological theories, laws, and explanations are useless; rather, they can be improved with the help of physics. The antireductionist holds that there is at least one biological theory, law, or explanation that cannot be reduced to physics. At least one biological theory, law, or explanation will gain nothing with the help of physics. These two competing claims are epistemic as opposed to ontological.
As far as methodology, reductionists advocate both top-down and bottom-up research. For example, in top-down research, discoveries in biology are to be ultimately be explained by physics. In bottom-up research, findings in the physical sciences such as organic chemistry, can lead to discoveries in biology. On antireductionism, there exists at least one discovery that cannot benefit from top-down or bottom-up research.
Since Watson and Crick’s discovery of the structure of DNA in 1953, some biologists have argued that there are irreducible explanations at different levels of organization in biology. For example, some antireductionists claim that Darwinian theories in molecular biology cannot be reduced to organic chemistry. Another antireductionist claim is that higher level biological properties affect lower level biological properties in what is called downward causation. If downward causation exists, then the higher level cannot be reduced to the lower level.
Arguments for Reductionism
- Since the physical facts fix the biological facts, this gives us reason to think that reduction is in principle possible, even if it is in practice impossible due to our limited cognitive abilities.
- The history of science is filled with reductions, e.g., the reduction of Kepler’s celestial laws and Galileo’s terrestrial theories to the more fundamental Newtonian theories. Other examples include the reduction of theories of gases to mechanics; Newton’s law to quantum mechanics and relativity; chemistry to quantum mechanics.
- Antireductionist argument: Suppose reduction has two requirements: (1) the laws of the reduced theory are derivable from the more fundamental theory, and (2) concepts, terms, kinds, and properties of the reduced theory can be defined in terms of the more fundamental theory. If this is the case then biology cannot be reduced for there are no biological laws. For example, Mendel’s “law” is not a law, so there can’t be a reduction.
- Reductionist rejoinder: Mendel’s “laws” do not need to be laws for it to be reduced. All that is needed is that the exceptions of Mendel’s “laws” (e.g., linkage, crossover, meiotic drive) be derived from more fundamental “laws” in molecular biology. This would require the concepts of Mendelian genetics be reduced to concepts in molecular biology, which is what Watson and Crick have already done.
Antireductionist arguments from molecular biology
- Antireductionists claim that the concept of gene in Mendelian genetics cannot be systematically linked up with the concept of gene in molecular biology. This is because on the theory of natural selection, biological structures like genes, cells, tissues, organs, etc., are selected for their function and differences in the microstructure won’t matter as long as the function remains constant. For example, if there is selection for oxygen-transport molecules, the result could be myoglobin or hemoglobin or something else. As long as they both provide the same function, natural selection is blind to their microstructure.
- Antireductionism accepts that two worlds with identical physical facts will have identical biological facts. But, given natural selection, two worlds with different physical facts could have the same biological facts. This means that the physical facts are not relevant to the biological facts.
- Even if there are no laws in biology, it is not general laws that are to be reduced but explanations that are particular to a specific circumstance. It is biological processes, events, systems, etc., that will be explained by physics.
- The limitations of reduction to physical explanations are epistemic, which can be overcome with advancements in imaging technology, computer calculations of chemical interactions, and computational bioinformatics.
Multiple realizability, supervenience, and antireductionism
- Most concepts, kinds, and properties in biology are functional. Functions can be multiply realized by different physical structures. For example, a hemoglobin gene can be multiply realized by different nucleic acid sequences. What is central to a gene, protein, organelle, cell, tissue, or organ is its functional role. To reduce biological states to physics would be to miss the point of biological explanation. What is important in biological explanation is the common function that these multiply realized states have.
- Consider genes that are switched on by proteins in the ovum of a mother. Even if genes are reduced to the vast disjunction of nucleic acid sequences that multiply realize them, explanations will still need to appeal to functional concepts like ‘mother’ and ‘ovum’. The point is that even after a reduction there will still need to be an appeal to functional concepts. (I think a similar issue occurs in behaviorism in philosophy of mind.)
- There is downward causation from the biological to the physical. In other words, some biological things cause physical things. This is another reason why there cannot be a reduction. For example, some cells can detect the activities of their surrounding cells, and this will cause cells to produce certain enzymes and molecules.
- Reductionist rejoinder: Downward causation leads to overdetermination in causes: if biological events cause physical events, and physical event cause physical events, then there are two different causes for the same effect, which is a problem.
Self-organization and reductionism
- (There is further argument between the reductionist and antireductionist about whether reductionists are allowed to use relational properties and properties resulting from combinations of parts.)
- (I didn’t fully understand the dialectic here with regards to Kauffman’s Boolean NK network, so I’ll skip it for now.)
Natural Selection and reduction
Consider the principle of natural selection (PNS): Whenever there is hereditary variation and fitness differences consequent on them, there will be differential reproduction. The reductionist needs to show how PNS can be reduced to physics.
Rosenberg, Alex & McShea, Daniel. Philosophy of Biology.