Evolution (of species) has no reverse

Biological evolution travels paths that are marked in the genes of successive species and that define certain anatomical structures and physiological functions that are printed on all derived genomes.
For example, when the first tetrapods (four-legged vertebrates) were defined from the first Tetrapodomorpha, which in turn evolved from the old fin-lobe fish (Sarcopterygii) about 390 million years ago (in the period Devonian medium) the bone structure of all vertebrates that followed them was defined. Thus, batracios, dinosaurs, various reptiles, birds, mammals, including primates, all have four limbs based on similar structures. These determined the varied ways of moving that all tetrapods have: walking, jumping, swimming, crawling, flying, adapting the limbs for different functions. The limbs became legs, wings, fins or similar organs. In all of them the articulated components that allow each of its functions to be developed were preserved.
In nature, there is no going back
The conclusion I want to reach is that there is no "reverse" in vertebrate evolution. In some cases the extremities atrophy because they are not necessary, they remain as vestiges of the old structures and even disappear (eg the offices).
Similar situations occur with other components of anatomical structures or physiological functions, such as digestive and circulatory systems, nervous system, etc.
In the development of the human brain there is the same type of processes. There is a “reptilian” brain inside, a mammalian brain around and finally a cortex that responds to the most recent anthropic evolution.
In all these cases it is noted that the original designs established certain guidelines that were preserved as the genomes evolved. But there was no basic design change or reverse. Only readjustments and aggregates.
One of the main reasons for this to happen in this way is that evolutionary changes are gradual and that in the successive series of changes each intermediate genome has to give rise to viable individuals. In other words, intermediate genomic individuals must all be viable, capable of competing in the natural environment and therefore able to reproduce.
 An analogy can be made in the development of urban matrices of cities.
Many modern cities developed in times when the transport roads were adapted to the means of transport corresponding to the time.
Thus, the first roads (for carts, riders, errands) were drawn avoiding flood areas (small ravines and water courses, swamps) and steep reliefs (ravines, rocky hills, etc). For this reason, they were no straight lines, normally they were winding tracks following geographical irregularities.
When the city grew, the old wagon roads became streets and avenues. In some cases, its route was modified, but frequently it kept giving rise to streets and avenues with winding paths. The most modern streets in later urbanizations, were designed according to particular local plans, often in the form of checkerboard or other geometric modalities.
This happened because it is difficult to substantially modify the basic urban plan of cities.
As time passes, the radical modifications that would be required would be very costly and there would be social and / or political resistance to carry them out. And so there are in many cities certain avenues with curvilinear routes different from adjacent streets that are only explained for historical reasons.
In Montevideo, it is the case of the Agraciada Avenue (old wagon road to the west) and 8 de Octubre Avenue- Maldonado Road (wagon road to the east). Rivadavia Avenue in Buenos Aires was in historical times (XViII century) the Camino Real to the west (cart road).
In Toronto, Canada (city where I lived a few years ago) there is a street called Dundas that has similar characteristics showing that in past times it had been a west-east road.
In the cities that were planned since its foundation (La Plata in Argentina, Brasilia in Brazil) urban matrices have not undergone major changes, but in practice they constitute a small minority in contemporary urban landscapes.