In biological terms, it is considered to extinction as a completely natural phenomenon resulting from a process in which a species originates from another-that is extinguished, "which usually occurs within several thousands or hundreds of thousands of years. Also missing those species that failed to adapt to the changes occurring in their habitat, which happened naturally and, in most cases, over long periods of time. Thus two-thirds or more of the animal species that have existed on the planet are now extinct. Unlike the extinctions that occurred in the past naturally, are current happening at a fast pace and not follow a natural inability to adapt the species, nor are the result of an evolutionary process, but is due to human activity that takes place.