One of the reasons put forward to explain the fact that we have yet to find evidence of other intelligent races in space (see Fermi Paradox), is that technological civilizations have a relatively short lifetime. For one reason or another, it is hypothesized, they are destroyed, possibly through ecological catastrophe or nuclear war (see extraterrestrial civilizations, hazards to). The problems currently besetting humankind in this regard may, the supposition goes, always occur and always prove insuperable. At the other extreme of speculation is the suggestion that a majority of extraterrestrial civilizations survive and continue to evolve indefinitely. If this is the case, then we might expect that there are intelligent races in the Galaxy which are both much older (see extraterrestrial civilizations, ancient) and further ahead of us (see extraterrestrial intelligence, more advanced than us).