 Beatty (2006), however, has shown that there are two different senses of ‘contingency’ in play in Gould’s work. In addition to what Beatty calls contingency as causal dependence—basically, sensitivity to initial conditions—there is a second form of contingency that Beatty initially called contingency as unpredictability, but now calls contingency per se (Beatty 2016). These two senses of contingency correspond with two versions of the famous thought experiment that Gould (1989) deployed. Sometimes, Gould imagines rewinding the tape of history, tweaking an upstream variable, and then playing the tape back. On other occasions, he talks about playing the tape back from the same initial conditions. Beatty (2016) thinks that both senses of ‘contingency’ are important, and he takes it that the second sense—contingency per se—must commit us to some sort of causal indeterminism. On the other hand, Turner (2011a) has tried to give an account of this second sense of contingency that is neutral with respect to determinism. His suggestion is that what Gould really cared about was random or unbiased macroevolutionary sorting. Processes such as coin tosses, or random genetic drift, can be random or unbiased (in a sense) without violating causal determinism. One way to think about this is by adopting a frequentist conception of probability: the outcome of a coin toss could be causally determined by small-scale physical influences, but the outcome is still random or unbiased in the sense that over a long series of trials, the ratio of heads to tails will approximate 50:50. This account is closely allied with Sepkoski’s (2016) suggestion that Gould’s metaphor of replaying the tape of history was rooted in his work on simulations of macroevolution in the 1970s. Turner (2015) has also argued that there is a connection between contingency, thus understood, and the notion of a passive evolutionary trend. 