Why send humans into space? Science and non-science motivations for human space flight

Although humans have been going into space for more than 50 years, it is still a fair question to ask why, given the expense and the risk. While there are scientific returns from having humans in space, it is often argued that science could be better served without a human presence. Here, I make a case for having a human presence in space to conduct a variety of scientific investigations, most notably those in the life sciences that involve humans as test subjects. There are aspects of the results from such investigations, and from the particular characteristics that make them especially challenging to perform, that are often overlooked. Non-scientific rationales for a human presence in space are also discussed briefly. Overall, when the relevance of the space sciences as a whole is considered, human space research has as much justification as other forms of space science, and in the end it is the quest for understanding our place in the universe that drives all of these scientific ventures.