 Wimsatt points out many other features that levels may have: For example, processes at higher levels tend to happen at slower rates than processes at lower levels, higher level properties are typically multiply realized by lower level properties, and higher-level causal relationships are dynamically autonomous in the sense of being largely independent of what happens at lower-levels. What differentiates different levels will also vary between instances, and may include part-whole distinctions, the magnitudes of forces by which things interact, or, pragmatically, considerations of size of different constituents. Importantly, Wimsatt also argues that in contexts where part-whole relationships become too complex, such as in the organization of biological systems, levels of organization break down, and in these cases a more appropriate organizational notion is “perspective” (Wimsatt 1994 [2007: 227]). Perspectives are (incomplete) accounts of systems based on a set of variables, and in contrast to levels, need not have any part-whole structure. For example, we can approach organisms from anatomical, physiological or genetic perspectives, each perspective coming with a proprietary set of variables.