Contingency and the Explanation of Macroevolutionary Trends

Once scientists identify a macroevolutionary trend, they typically ask whether it is passive and generated by a random walk, or driven and generated by a directional bias in the state space. My talk will explore the connection between the passive/driven distinction and questions about the contingency of evolutionary history. I will suggest that the historical processes that generate passive trends exhibit greater contingency, whereas those that generate driven trends exhibit less contingency.