There is certainly no forwards and also no backwards. It is just an on going optimization process. It is on going because the constraints change. Most of the co

There is certainly no forwards and also no backwards. It is just an on going optimization process. It is on going because the constraints change. Most of the constraints can be summed up under the general term "environment". The effects of the climatic environment can be grasped more easily. However it is harder to grasp how all(or most) of the constraints feeding into each other, across both time and space. With that said, life as we know it has a penalty on needless complexity. And, what does complex mean anyway? Complex genotype or complex phenotype? What is a good metric for measuring each one? Whatever the metrics are, it cannot be said that they are related monotonically. In this sense, we have four permutations of complexity i.e.[simple genotype, simple phenotype], [simple genotype, complex phenotype], [complex genotype, simple phenotype] and [complex genotype, complex phenotype]. Life as we know it is defined in the whereabouts of the genotype level. The "penalty" is on the [complex genotype, complex phenotype] type of complexity primarily because of the inaccuracy in the cell division process/processes (life as we know it!!). With many points that can go wrong in the foundation(cells->chromosomes->genes -- genotype), you don't want many points that can go wrong in the outcome(phenotype). Of course life can (and does) beef up the genotype level with more complexity to try and ensure a rock solid phenotype (complex or not) but all factors withstanding, a simpler phenotype is easier to maintain.