The understanding of the mechanisms that allow the origin of species has shed light on many processes such as speciation, adaptation and extinction, but how to explain the existence of such a huge diversity of species on Earth still remains a mystery. Many theories and evidence have corroborated the processes that allow species to evolve or become extinct. Currently there are different hypotheses but no clear demonstrations of the factors that maintain the species diversity of ecosystems. Those based on competitive principles have been criticized from both theoretical and empirical approaches. Only by studying biodiversity in the context of evolution, natural history and ecology (taking into consideration the avoidance of competition and dispersal abilities, the phenotypic plasticity, the heterogeneous landscape, the facilitation and the endogenosymbiosis) we can understand values and gaps of past theories trying to provide a broader understanding of life on Earth towards a Unified Theory of Biodiversity.