Watching Cowboys & Aliens, I couldn’t help but think about the evolution of the intellectual insect-like aliens (a science fiction cliche) who have a pair of arms in the normal place and a smaller pair within the chest cavity: in order to access the small hands, they have to expose their hearts.
The body plan raises some interesting questions about their evolution. Exposing the heart to use the small hands is too risky to be so strongly selected for in their ancestors. And, the location of the arms doesn’t mesh with developmental genetics unless they have been mucking about with their sonic hedgehog genes. But, if they spliced their sonic hedgehog to get the precision hands, how did they develop the technology without them? Perhaps they are more like Daleks and Cybermen, having put at least part of themselves inside a body that serves as armor.
One last thought, they were pretty small-brained and big bodied (more evidence for the Dalek/Cyberman model) which makes me wonder about their material culture a bit unless they are like modern humans with smaller (compared to archaic humans) but more efficient brains.
The Smell of Evolution 