<p>Our only example of life is that of Earth- which is a single lineage. We know very little about what life would look like if we found evidence of a second origin. Yet there are some universal features of geometry, mechanics, and chemistry that have predictable biological consequences. The surface-to-volume ratio property of geometry, for example, places a maximum limit on the size of unassisted cells in a given environment. This effect is universal, interesting, not vague, and not arbitrary. Furthermore, there are some problems in the universe that life must invariably solve if it is to persist, such as resistance to radiation, faithful inheritance, and resistance to environmental pressures. At least with respect to these universal problems, some solutions must consistently emerge.</p><p> In this dissertation, I develop and defend my own account of universal biology, the study of non-vague, non-arbitrary, non-accidental, universal generalizations in biology. In my account, a candidate biological generalization is assessed in terms of the assumptions it makes. A successful claim is accepted only if its justification necessarily makes reference to principles of evolution and makes no reference to contingent facts of life on Earth. In this way, we can assess the robustness with which generalizations can be expected to hold. I contend that using a stringent-enough causal analysis, we are able to gather insight into the nature of life everywhere. Life on Earth may be our single example of life, but this is merely a reason to be cautious in our approach to life in the universe, not a reason to give up altogether.</p> / Dissertation