Evolution and complexity

"Nature works by steps. The atoms form molecules, the molecules form bases, the bases direct the formation of amino acids, the amino acids form proteins, and proteins work in cells. The cells make up first of all the simple animals, and then the sophisticated ones, climbing step by step. The stable units that compose one level or stratum are the raw material for random encounters which produce higher configurations, some of which will chance to be stable... Evolution is the climbing of a ladder from simple to complex by steps, each of which is stable in itself."

Jacob Bronowski (1973)

Does evolution lead to greater complexity? It is obvious that it can, but it would be erroneous to believe that this is always the case [Ray94, p. 14].

But when evolutionary pressues demand a adequate responses variant circumstances, complexity is favoured [Gea05].

Also sharing this view on stratum theory and its implications are, Butler (1878, 1880), van den Tweel (1988) and Vroon [Vro89, p. 175]. It corresponds with the observation that cognitively higher species (which exhibit more intelligent behavior) tend to be more recent products of evolutions [MSS95].

According to Heylighen, functional complexification follows from the need to increase the variety of actions in order to cope with more diverse environmental perturbations, and the need to integrate actions into higher-order complexes in order to minimize the difficulty of decision-making. Both processes produce a hierarchy of nested supersystems or metasystems, and tend to be self-reinforcing. Though simplicity is a selective factor, it does not tend to arrest or reverse overall complexification. Increase in the absolute components of fitness, which is associated with complexification, defines a preferred direction for evolution, although the process remains wholly unpredictable. [Hey96]