   Linking this debate to philosophical ideas about causation can help us evaluate whether evolutionary constraints count as genuine alternatives. Constraints are defined as biases or limitations on the production of variation. From the perspective of causation, this is a heterogeneous combination. Constraints that bias a lineage towards certain evolutionary trajectories look like productive probabilistic causes, and avoid certain conceptual entanglements that face boundaries or limitations. Innovations in the developmental makeup of an organism can make new changes and subsequent evolutionary trajectories more likely, a hallmark of a causal factor. This helps clarify the importance of evolutionary innovation. Innovations that produce biases may be crucial to explaining major evolutionary transitions, such as the emergence of multicellularity (Sterelny 2008). When certain changes make new evolutionary outcomes more likely they are part of the explanation of those new outcomes. Such biases count as probabilistic causal influences since they change the probability of a lineage taking certain evolutionary trajectories (Hitchcock 2008).