"The fact being that almost any cargo along these lines (made of the elements produced across the universe by stellar nucleosynthesis and supernovae) is going t

"The fact being that almost any cargo along these lines (made of the elements produced across the universe by stellar nucleosynthesis and supernovae) is going to be a) most likely available in any system already, b) definitely available for the taking from billions of unoccupied regions of space." Yet, for example in Australia (at least Tasmania) under British colonial period, raw materials such as wood for housing was imported from Carelia (through Britain), although local better materials (e.g. rooting-resistant Huon pine trees) could be found in abundance. Sometimes the logic is defied by other human behavioral factors, sometimes the simple economical reasoning does not tell the whole story, so I wouldn't be surprised if water will be traded. "A few billion years of natural selection and evolution on any given planet will produce an array of wonderful and useful lifeforms, that could be unique enough to be of interest elsewhere." Considering our history in messing up the natural habitats and ecosystems, and also considering that we ended up with restrictions on introducing living organisms in many places here on Earth, I'm also not surprised if stronger restriction will be set up for trading such things on even more separate environments such as planets. I see instead good prospects for interstellar tourism, with clients willing to travel vast distances just to see those living "Bunny rabbits and butterflies" in their natural environment.