It seems feasible to create a large artificial environment on Earth, probably at the highest elevation possible (Himalayas??), like a large sealed sphere, and get healthy male and female adult volunteers to commit to living out their lives there, and while training them in Martian survival techniques, gradually lower the atmospheric pressure and the temperature inside the sphere, while constantly monitoring their bodily responses so as not to exceed the adaptability rates of their bodies. At the same time, the cosmic and gamma and other solar rays from which Mars' atmosphere affords little protection, would be gradually increased, again staying within their bodies' ability to adapt and to develop defensive properties.
This process would probably take 3 or 4 generations, as the volunteers would certainly have offspring in this pseudo-Martian environment, and those children in turn would have offspring, until about 80 years down the line, a generation of (hopefully) physically and psychologically healthy people would come into being who would require only minimal, if any, life-support systems on the actual planet Mars. THEN we could send mankind to Mars to colonize and explore. Waddaya think, people?