 Many paleobiologists have assumed that driven trends must be driven by natural selection. For example, if body size increase is driven, surely that means that larger body size has conferred some survival or reproductive advantage (Hone &amp; Benton 2005). McShea (2005) and McShea and Brandon (2010) have forcefully challenged that assumption. McShea (2005) argues that increase in structural complexity is a driven trend, but one that need not be driven by selection. That is because increasing structural complexity might just be the zero-force condition for evolving systems, an idea that McShea and Brandon (2010) develop in great detail. McShea and Brandon’s zero-force evolutionary law—or ZFEL—has elicited critical responses from other philosophers (Barrett, et al. 2012). Whereas traditional evolutionary thinkers, from Darwin on down, assumed that natural selection would have to explain complexity increase, McShea and Brandon see complexity increase as the default expectation, and they invoke selection to explain deviations from that default expectation—such as cases of eye loss in cave-dwelling species. They treat eye loss in cave dwellers as a case where natural selection favors a reduction in structural complexity. Alternatively, O’Malley, Wideman, &amp; Ruiz-Trillo (2016) consider the potentially wide-ranging and macroevolutionary role of simplification in conferring “adaptive” advantage.