If I were asked so summarize life on Earth, the phrase "variation on a theme" seems appropriate. So many very different species share so much in common. For example almost all multicellurlar organisms have teeth, stomach, intestines, hearts, livers, brains, arteries, veins, blood, skin, eyes, lungs, nostrils, mouth, etc. Why is there so much consistency...so much sameness...various variations on a theme? Thre is a lot of similar architecture. Is it likely that if we were to find another planet similar to Earth and life, if it existed there, would be very similar to what we find on Earth? Is it likely we will find the same architecture for life elsewhere in the Universe, lungs, heart, liver, etc? Why is there no radically different kind of architecture or is there something intresically critical to the basic design we see here on Earth...given the environmental circumstances present on Earth?