The following selection paraphrased from the article on ‘Morality and Evolutionary Biology’ from Stanford Encyclopedia of Philosophy is an objection to metaphysical naturalism, but it is also relevant to ethics as well.
The Challenge from Irreducible Pluralism
“Lets take mathematics and evolution as an example. If we say mathematical proposition x (e.g. ‘There is always a prime number between the integer n and 2n.’ ), we can determine the truth of this proposition by use of mathematical reasoning. We do not say x is true because there is an evolutionary advantage to x being true. A moral realist would argue that moral philosophy is similar to mathematics ( or physics, chemistry, etc). For example the statement that interracial marriages is wrong one can use moral reason to say this statement is false in light of the moral truth that all human beings have the same moral worth. In the same way we can use autonomous mathematical reason to evaluate mathematics we can use autonomous moral reason to evaluate ethics. Of course moral reasoning can be influenced by culture and biological factors and there are other (would argue less) plausible moral approaches like expressivism or error theory than moral realism, but the statement all ethics is simply evolutionary biology seems very premature.”
This selection is probably the most interesting interpretation/rebuttal of ‘reductionism’, a concept commonly used but rarely well-defined. It claims that the formal sciences are in some way ‘autonomous’; they give themselves their own principles. Frege famously defended this in his conflict with Husserl’s early psychologism. According to this modern variety of “Platonism”, the principles of a formal science cannot be derived from any empirical field. If this is true of mathematics and logic, then is seems as though this sets a precedent for the “is/ought” distinction.If a priori knowldege were shown to have a separate basis from a posteriori knowledge, then it could be used to clarify the separation of fact and value. It would seem that Platonism in this sense give us at least two realms of beings who are independent and yet have a certain level of ‘pre-established harmony’ between them. Math for example, is useful and authoritative for many empirical fields from physics to economics. How this could be so was what Kant sought to explain, and his solution sought to bring both formal and ethical beings into relation with the empirical.
My basic idea for naturalistic metaphysics is this: mathematics performs a cognitive function and therefore has adaptive value in light of this function. In order to perform this function, it needs to satisfy certain formal conditions. We are constrained by the definitions of mathematical beings because changing those definitions in the least destroys the functional and adaptive value of math.
Arithmetic is founded on nothing but the set of sets whose members map onto each other. “Mapping” means that each member of one set has a unique counterpart in every other set with the same number of members. This is the only way to clearly and primitively define integers, and all other math is founded on this simple set of interrelated definitions. If you change the defintion of one interger, it becomes the same as its neighbor and leaves a gap. Thus there is only one possible set of integers, and therfore only one possible way to relate them, meaning there is only one possible multiplication table.
If you changed the definition of one of the integers, it would also lose it’s adaptive value. Mathematics is only “autonomous” because each mathematical being has NO autonomy from most if not all mathematical beings, and all are dependent on the simple idea of the relationship of sets mapping onto each other. This idea is in turn is derived from problems like figuring out:
- how to share a big basket of fruit
- if a war party is evenly matched by the enemy
- if someone has stolen some of our cattle
If basic arithmetic can’t accomplish this, it’s useless crap. I’m sure I oversimplified and left out some other items ( such as the fact that there are multiple mathematical foundational theories ), but I hope this clarifies my overly-short answer of how evolution can produce creatures with a priori knowledge of the ‘universal language’ of mathematics. In this view, some ethical principles can have something like this sort of a priori validity if we can find a suitable starting point. For math, the starting point I used was defining the integers through set theory. The starting point for ethics could start with the game theory of the iterated Prisoner’s Dilemma. In this dilemma, there are only a finite number of Evolutionary Stable Strategy-schemas, i.e., definable sets of strategies that work. Examples of a strategy-schemas include “Initially Benevolent Strategies” ( strategies that do not betray without being betrayed first) and ” 2-turn Forgiving Strategies” ( strategies that stop betraying in revenge after two turns without a betrayal ). Perhaps there’s a better starting point than the Prisoner’s Dilemma. But this is just to illustrate possibility of how to get started generating ethical rules from evolutionary game theory. This could fulfill the dream of Plato, Kant and other ethical rationalists while paying proper respect to modern science.