In the history of life, the facile appearance of increased complexity was achieved mostly through modularity. Once a structure is established, the potential exists for fractal repetition for distinct functionality.
In modern complex organisms, novel adaptations result mostly from reorganization of existing structures. ~ Russian evolutionary biologist Alexander Badyaev
Organs are macroscopic extensions of the organelles within cells. The main innovation in plants was modular: the evolution of semi-autonomous regions embodied in the embryonic meristems of roots and shoots. Grasses amply illustrate this principle at work.
Energy efficiency mediates the interactions of physics and chemistry. Such frugality is also an apparent inclination in evolutionary developments. Photosynthesis and vision are obvious examples of astonishing efficiency in taking advantage of light.
Economy as an inclination might seem to work against complexity. Yet, given the vast diversity of elaborated traits in Nature, there is abundant evidence that it does not. Instead, Nature often hones the functionality of multifaceted traits toward efficiency, as with photosynthesis and vision.
That is not to say that parsimony does not affect complexity. Efficiency acts as a constraint on the directions that evolutionary developments take. Bottom-up physio-chemical constraints pave the avenues of evolution. Then there are strategic trade-offs – life-history variables – that affect tactical approaches. Evolution may not have an overarching vector, but it does play by a rulebook (which is fantastic in its intricacy).
20th-century biology was structured according to a linear Newtonian worldview – not the kind of thinking that’s needed to study evolution. It doesn’t help you understand the nature of systems. Molecular biologists were so set about linearity that when the gene came along, they took the gene to be the be-all and end-all of basic biology. That comes out of thinking in terms of particles and linear interactions. Evolution is the quintessential nonlinear dynamics problem. ~ American microbiologist and physicist Carl Woese