The effort to mirror objects in the world in our artistic creations reaches back into prehistory.
The stone objects, dated from 50,000 years ago, look like the ones made by capuchin monkeys today.
The atomic element boron is essential for life, but how do you get it from stars to plants and animals?
As every medical student comes to learn when first dissecting the human body at medical school, our limbs are almost entirely composed of muscles.
Being terrestrial is one obvious requirement. No fully aquatic species could master fire and thus develop metallurgy.