 Nonetheless, it is possible to view the experiment as performed in 1957 as strong evidence for the semi-conservative mechanism. Weber (2009) argues that this mechanism is part of the best explanation of Meselson’s and Stahl’s data. By “data”, Weber means the actual bands observed. Why is this explanation better than the one involving the conservative scheme and end-to-end associations of heavy and light DNA? To be consistent with some data is not the same as being a good explanation of the data. The explanation using the semi-conservative scheme was better because it showed directly how the nitrogen is distributed evenly. By contrast, the alternative explanation requires the additional assumption that the parental and filial DNA somehow remain covalently attached together after replication. This assumption wasn’t part of the mechanism, therefore the latter explanation was incomplete. A complete explanation is always better than an incomplete one; no principle of parsimony need be invoked here.