Zero Force Evolutionary Law

The Zero-Force Evolutionary Law, or ZFEL, is a theory proposed by Robert Brandon and Dan McShea regarding the evolution of diversity and complexity. Brandon and McShea define diversity and complexity in terms of variation, diversity being variation between organisms and complexity being variation among parts within an organism. McShea had previously defined a part as "a system that is both integrated internally and isolated from its surround," giving the digestive tract, epidermis, and skeleton, as examples. As an analogue to the theory of relativity, the theory has a special and general formulation. The special formulation states "in an evolutionary system in which there is variation and heredity, in the absence of natural selection, other forces, or constraints on diversity or complexity, diversity and complexity will increase on average" while the general formulation states that "in an evolutionary system in which there is variation and heredity, there is a tendency for diversity and complexity to increase, one that is always present but may be opposed or augmented by natural selection, other forces, or constraints acting on diversity or complexity". The rationale for the claim is that as replicators such as genes replicate, errors will accumulate. If not eliminated by negative selection, these variations will lead to greater diversity and complexity.