Evolution is fantastic at Research and Development. It's all it does, really Constantly testing little tweaks to an existing model, until it finds something that works super well in a very specific set of circumstances. The problem is, with rare exceptions, because evolution is incredibly influenced by the environment, the resulting creatures don't have extraordinary range. Internal thermal regulation requires specific and constant external temperatures, or diet is based around a singular and very limited source of a particular plant, or a hundred different ways that evolution locks it's creations into a very narrow slot.
Humans are an exception. We can live, and live comfortably, pretty much anywhere on Earth, and do so with very little additional adaptation. In fact, the only significant difference between humans living in the Afar Region of Africa, the hottest inhabited place on the globe, and Yakutsk, Siberia, the coldest, is a couple layers of clothing and a change in skin colour. That's remarkable for a tenuously balanced ape that was originally built for tree and field life in temperate Africa. And the number of other species that have that amount of global freedom can be counted on one hand.
But that's Earth. Once you step outside that comfort zone, life becomes very hard to maintain without significant scientific intervention. In fact, it becomes downright impossible. As Neil deGrasse Tyson quickly explains, humans do very well here, and very poorly everywhere else. I'd like to see an extended version of this video, where he discusses the various moons of Jupiter and Saturn that he'll probably eventually land on, but his answer would be the same: too cold, too breathless. It is a little slice of solace that evolution is a universal force, and that once we land on Mars, loaded up with enough kit to make certain we don't end up like Cohaagen at the end of Total Recall, we will adapt to the existing environment. Over generations, bone and muscle density will change based on the lower gravity, and there will come a point when those Martian Humans wouldn't be able to step foot on Earth without going all sloth-on-a-highway.
And at that point, a Martian Tyson will look to Earth and say to his fellows, "don't go there."
Via The Mary Sue.