The human lineage of genus Homo has reduced from several species co-existing on Earth to just one — all others became extinct before the end of the last Ice age. This illustrates that Homo sapiens is not immune to planetary disaster and that human survival may be better assured through the colonization of space. Although space colonies do not yet exist, humans have had a continuous space presence since 2000 in the form of the International Space Station. Life support systems that enable people to live in space may also allow them to survive hazardous events. Multiple locations Expanding the living area of the human species increases the mean distance between humans and any known hazardous event. People closest to the event are most likely to be killed or injured; people farthest from the event are most likely to survive. Increasing the number of places where humans live also helps to prevent extinction. For example, if a massive impact event occurred on Earth without warning, the human species could possibly become extinct; its art, culture and technology would be lost. However, if humans had previously colonized locations outside Earth, the opportunities for the survival and recovery of the species would be greater. Objections Many challenges arise when travelling in outer space. One of the biggest issues that may affect the human body is interstellar radiation. While the Earth's magnetic field and atmosphere protects all living forms on the planet, this cannot be said for outer space. According to researchers from the University of Rochester Medical Center, a radiation equivalent to a mission to Mars can cause serious brain damage such as cognition problems and Alzheimer's disease. Space science The observation and study of space protects Earth, as space hazards can be seen in advance and, if discovered early enough, acted against. Near-Earth objects Near-Earth objects (NEOs) are asteroids, comets and large meteoroids that come close to or collide with Earth. Spaceguard is the collective name for some of the efforts to discover and study NEOs, though these efforts are not sufficiently funded. Critique Some more contemporary reasons for space as a solution to survival have been identified as imperialist reasoning for space exploration, only relocating collective shortcomings and not solving them. See also References Further reading Pale Blue Dot: A Vision of the Human Future in Space, Carl Sagan, 1994, Realspace: The Fate of Physical Presence in the Digital Age,