http://www.sciencemag.org/news/2015/05/space-radiation-may-d...
After letting the mice rest for 6 weeks, the team put them through a battery of cognitive tests, including a task that required the rodents to distinguish between familiar and novel objects, such as toys. The mice hammered by radiation were “severely compromised” on several measures compared with an unexposed control group, Limoli says. Control mice, for example, spent more time sniffing around a new item placed in their cages than investigating familiar objects—a sign that their ability to react to novelty was intact. Irradiated mice, in contrast, spent equal time exploring new and old items, suggesting their ability to learn and remember new information about their environment had been impaired.
Talk of mars colonization is riddled with myopic assumptions about something we barely understand. Focusing on those few issues we may have in hand to the exclusion of the many critical unsolved problems is troubling.
They also mention that is not a showstopper and that it can potentially be countered with entertainment and exercise.
It also remains to be seen what the effect is like on humans. Might be negligible on a mars trip.
A more realistic approach to mitigating the issue is in my opinion to have rotating crews. They would spend most of their time in underground shelters, and only some minor fraction of their time doing surface work. Advances in medicine, specifically in regard to cancer, along with minimizing exposure time, is what I believe will make the risk low enough to be within acceptable bounds.
This is in large part why I think that Mars is continent upon offworld mining and construction industry, rather than the other way around.
They're typically not qualified for much of the labor needed in a colony, but that's another problem. We only need a tiny percentage of the eligible. Some people really have different priorities than confort and longevity. Many of them are risking their lives on Everest, for much less.
If there was no other way, as it frankly was in the age sail, and human lives simply had to be the currency of progress then so be it. We don’t live in those times, and we definitely have options other than sacrificing some people; they’re just more expensive, difficult options.