Week 2: Philosophy and Biology

History of Biology: Landmarks

1839: Schwann's cell doctrine

1859: Darwin's theory of evolution by natural selection

1865: Mendel's genetic theory of heredity

1930: Fisher's synthesis of natural selection and genetics

1953: Watson and Crick's double helix structure of DNA

Questions in the philosophy of biology: examples

What is the nature of theories such as evolution and genetics?

What is the nature of biological explanations?

Is biology reducible to physics and chemistry?.

The Problem of Reduction


A scientific level is a system of entities and behaviors that require explanation.

Levels: large scale account

  1. Physics/chemistry: quarks, atoms, molecules
  2. Biology: cells, organs, organisms, species
  3. Psychology: minds, brains
  4. Sociology: groups of people

Note: there are many sublevels within these general levels.

What is the relation between levels?

Independence: Changes at the higher level are not causally related to changes at lower levels. E.g. dualism.

Reduction: All changes at the higher level can be explained by changes at the lower level. E.g. chemistry is reducible to physics, because behavior of molecules is completely determined by the structure and behavior of atoms. Example: game of life.

Supervenience: It is impossible for there to be changes at the higher level without corresponding changes at the lower level. This is looser than reduction, since the correspondence may not be known. E.g. functionalism in the philosophy of mind: mental changes are physical changes, but mind does not reduce to any particular kind of physical system.

Emergence (Humphreys): The higher level has qualitatively novel features that do not exist at lower levels, such as new causal properties and structure that is unpredictable from lower level theories, and these features are autonomous from lower level changes.

Birelational mechanisms: The higher and lower level mechanisms are interrelated. The entities at the higher level decompose into entities at the lower level, and many changes at the higher level can be explained in terms of the changes at the lower level. But some of the changes at the lower level depend on aspects of the higher level. E.g. psychological explanations may depend on how people perceive the groups they belong to.

Discussion Questions for Week 3

  1. What is a mechanism?
  2. How do mechanistic explanations differ from nomological explanations in terms of laws?
  3. How can mechanisms be represented? How is time represented?
  4. How are mechanisms discovered? How does decomposition work?
  5. How are mechanistic explanations evaluated?
  6. In the study of mechanisms, how are metaphysics and epistemology interrelated?
  7. What phenomena seem to you least amenable to mechanistic explanation?



Life, Mind, and Disease

Computational Epistemology Laboratory.

Paul Thagard

This page updated Sept. 20, 2004