3 On Complexity Science

Complex versus Complicated.

Complex systems are systems with many interconnected parts that exhibit emergent behavior.

Stable macroscopic patterns arising from local interaction of agents (Epstein, 1999).

In mathematical terms, the interactions of interest are non-linear (Holland, 2014).

When the aggregate exhibits properties not attained by summation (Holland, 2014).

The behavior of each part don’t explain how they behave collectively.

Emergence: new properties that arise from the interactions of the parts of a system, which are not present in the parts themselves. Collective behavior. Aggregate behavior.

You are dealing with an emergence phenomenon when there is no need to look under the hood (Complexity Explorer Lecture, 2023).

Figure 3.1: An illustration depicting how the human circadian clock system works. (A) The circadian timing system receives light signals through the eyes, which are processed by the brain’s central clock, the suprachiasmatic nucleus (SCN). This clock helps to orchestrate peripheral clocks, regulating body functions like hormone release, metabolism, and temperature. Other factors like feeding schedules and exercise also influence this process, ensuring the synchronization of body systems like immunity and metabolism. (B) Specific brain cells and chemicals manage this timing by adjusting the activity of neurons, which helps reset the clock and keeps it in tune with day-night cycles. These neurons also influence clocks in other body parts via neuronal and hormonal signals. (C) At a molecular level, a network of genes and proteins operates in a feedback loop, maintaining near 24-hour cycles. This ensures that various body systems, such as metabolism and immune function, follow daily rhythms.

The result of a juggling act of billions of years of evolution. There are no specific functions. There’s no proposed goal.

Levels of description (Nicolis & Nicolis, 2012). Starting in the cell nucleus with the molecular clock, then the cell, the tissue, the organ following to stable macroscopic patterns of circadian rhythms in behavior and physiology.

If you think about it, the extensive clock control is like a finely-tuned choreography. Everything is organized to happen at the right time, just like a Rube Goldberg machine (Merrow & Roenneberg, 2020).

Circadian clocks regulate and/or modulate functions at all levels, ranging from gene expression and physiology to behavior and cogitation (Roenneberg et al., 2007).

It’s an emergent phenomenon. It’s not a property of the parts themselves. It’s a property of the system as a whole.

“[…] involve great numbers of parts undergoing a kaleidoscopic array of simultaneous interactions.” (Holland, 1992)

In complex adaptive systems, emergent properties often occur when coevolving signals and boundaries generate new levels of organization (Holland, 2012).

A system of many interacting parts where the system is more than just the sum of its parts (Mark Newman in Mitchell (2013)).

A system that involves a large number of parts undergoing a kaleidoscopic array of simultaneous interactions, exhibiting aggregate behavior that cannot be simply derived from the actions of the individual parts (Holland, 1992).

Systems with many connected agents that interact and exhibit self-organization and emergence behavior, all without the need for a central controller (Camilo Rodrigues Neto).

Dialectics at its finest (my working definition).

Complexity science seeks to explain emergent phenomena or mechanisms that “screen-off” their constituent parts and thereby allow new levels of description and understanding (Krakauer & Wolpert, 2024).

Other concepts: chaos, power laws & factor sparsity, feedback loops, robustness, equilibrium states, path dependence, leverage points

Approaches to study and model circadian clocks.