**5. Discussion**

If Prehistory is understood as the pursuit of the stability provided by settling, it can be seen that the equivalent energy decreased as man approaches his objective. However, the last model, the adobe stepped dwellings, revitalized that value. It is necessary to take into account that, as long as the sedentary lifestyle went forward, the global temperatures rose progressively too, until reaching a value that made settling and agriculture viable. The greatest problem faced by the dwellings in the temperate climates, where man could live on agriculture, was that the temperatures were significantly higher in summer than in the past. That was probably the main problem to be solved, since winter could be solved, if necessary, by means of hearths. As Danny H. W. Li [85] asserted, when the temperatures began to rise, as happened 18,000 years ago, when agriculture was established, the greatest problem to be faced was the summer, and the dwellings must adapt to it. Consequently, the energy demand rises in the arid regions during these periods.

This way, of the three aforementioned sedentary dwellings, the one that isolates more energy, the model from New Mexico, is the one located in the zone that reached the highest temperatures. Facing the consequent increment of energy demand that took place during the summer, the sedentary human being designed the sedentary dwelling that isolated the highest amount of energy with respect to the known models that let him clear the largest amount of terrain for agriculture, that is to say, the orthogonal models. It would also be important to point out that the color of the envelopes would have influenced these results. As was demonstrated, the use of light colors in hot areas, such as the ones used in the pueblos, and dark colors in cold regions, such as the envelope of the earthlodge, reduce

the energy consumption of the dwellings [86]. The main solution proposed in the aforementioned research [85] for this problem consists of increasing the adaptability of the dwellings built in these regions. This idea could be reinforced by analyzing the tipis, built in one of the hottest areas of North America, the Great Plains. The versatility of this shelter is one of its strengths, thanks both to its mobile envelope and to its morphology. Its smoke hole allows people to control the indoor ventilation and the indoor temperature at the same time, both at will, by means of two poles. No less important was the airtightness achieved by the envelope seams. This factor [87,88] was determinant to provide a comfortable indoor ambient. In the same way, it can be easily turned around in order to avoid strong winds [18] during a storm, since its structure is not symmetrical. This efficient design is contained in the old legend which explains the origin of tipis, since, according to it, the shape of the cottonwood leaves inspired its triangular shape. Both of them, the tipis and the leaves, use the Venturi effect to withstand wind and, in the case of tipis, improve indoor ventilation. Something similar happens in Acoma dwellings, whose shape, according to a legend, is based on the shape of the surrounding mountains. The airflow system that was used to dry the harvests on the houses' roofs works in the same way that the airflows move in the slopes of the mountains. During the day, the airflow rises from the valley, since the peak of the mountain is cooler and hot air is lighter than cool air, whereas during the night, the cycle is reversed and the air that rests in the peak turns cooler and descends to the valleys. This is the physical principle that Ralph Knowles, professor and member of the American Solar Energy Society, had already intuited and described in 1974. Thus, the mountains are not only a metaphorical reference to the design of these dwellings, but they also influence on their operation and distribution. These ideas go in the same direction as the results of the research carried out by Zahraa Saiyed and Paul D. Irwinb [89]. As they conclude, Native American legends reflect a knowledge about the environment which goes further than symbolism. These stories indicate that Native American Indians deeply knew how their surrounding environment worked, and that fact let them use the resources at their disposal in a respectful and efficient way. Moreover, as can be seen in the research developed by César J. Pérez and Carl A. Smith [90], the indigenous techniques, the so-called Indigenous Knowledge Systems (IKS), which often underlay these old stories, can be very useful for the environment protection at present.

The nomad lifestyle is more closely linked to nature than the sedentary lifestyle is. This can be seen by analyzing the Navaho culture, as the research presented by Len Necefer concludes [91]. This fact also affects their dwellings, the hogans. One of their most remarkable features is that their smoke hole cannot be closed. Unlike the tipis, whose smoke hole controls the exit of air and smoke, the hogan's can never be closed, as Thibony explains [29]: "Visitors ask what happens when it rains or snow", said a Navajo working at the visitor center. "They want to know if they cover the smoke hole. '*You let things happen*' I tell them. '*You let the rain come in. The dome represents the sky, and the floor is the earth. The earth shouldn't be covered up. It reminds you of who you are and where you came from. The hogan places you where you belong. You take your identity from it*'". Features like this allow understanding how a culture works and the stance their members take in relation to current challenges, such as the energy consumption or the environmental resources management.
