Functional information

The concept of functional information is an attempt to rigorously define the information content of biological systems. The concept was originated by a group led by Jack W. Szostak in 2003.^[1]

Definition

They define functional information as follows:^[2][3]

• the concept of degree of function is introduced, where the degree of function ${\displaystyle E_{x}}$ is a non-negative objective measure of the capability of system ${\displaystyle E}$ to do the physical function ${\displaystyle x}$.
• the fraction of possible configurations of the system that can achieve at least a particular level of function ${\displaystyle \theta }$ in regard to the physical function ${\displaystyle x}$ is defined to be ${\displaystyle F(E_{x}\geq \theta )}$
• the functional information relative to a given level of function ${\displaystyle E_{x}=\theta }$ is defined as ${\displaystyle I(E_{x}\geq \theta )=-log_{2}F(E_{x}\geq \theta )}$

This leads to two conclusions:

• because all possible configurations can achieve zero or more functionality, that is to say ${\displaystyle F(E_{x}\geq 0)=1}$, the minimum possible functional information for a system is ${\displaystyle -log_{2}1}$, which is zero.
• for the highest possible level of a degree of function of a system ${\displaystyle E_{x}=\theta _{max}}$, there will be a well defined ${\displaystyle I(E_{x}=\theta _{max})=-log_{2}F(E_{x}=\theta _{max})}$

Note that functional information of a system ${\displaystyle E}$ must always be defined relative to a specific function ${\displaystyle x}$, without a choice of which it has no meaning.

Proposed law of increasing functional information

In 2025, a group of researchers proposed a law of increasing functional information, that asserts that a tendency to increase in functional information is an inherent property of the universe, encompassing both biological and non-biological systems.^[4][5][6]