What is the current science regarding the human habitation of Mars?
Current technology has shown the surface of Mars to be extremely dry, without standing, atmospheric, or surface water. This is combined with an extremely thin atmosphere to create conditions hostile to human habitation. People living on the surface of Mars would either need the entire planet to be terraformed -- the atmosphere thickened to be rich in oxygen and water -- or themselves genetically engineered to survive with little atmospheric content (which would not solve the problem of solar radiation, unblocked by the thin atmosphere). Both of these options are centuries in the future with existing technology. The only current option for colonizing Mars are enclosed habitats with their own isolated atmosphere, similar to those used in space travel; however, a trip to Mars has been planned/postponed since the Moon landing in 1969, and is not considered of importance today considering the other problems the world is facing.
Some Astrophysists have studied horse shoe shaped trenches and other geographical features similar to ones found on Earth that we developed due to short lived but colossal floods thousands of years ago. This suggests that at some point of time there was vast quantitiy of water in liquid form on the surface of mars.
However this does not confirms whether there were ever such conditions on mars that supported life forms.
As far as living conditions at present on the surface of the mars are concerned, no life forms exists or are assumed to exist at mars.