Macroevolution

 

Patterns in the fossil record have inspired diverse interpretations for more than two hundred years. In particular, whether macroevolutionary patterns display some type of historical directionality has been much debated. Those who have claimed to identify a particular empirical signature or indicator of directionality in the fossil record have often provided controversial interpretations of its source, sometimes claiming teleological movement toward specific taxa (especially humans) or generalized outcomes (e.g., a progressive increase of complexity). The potential sources of directionality advanced in these interpretations have been diverse and include both properties intrinsic to the lineages represented by fossils and properties extrinsic to the lineages represented by changing environmental conditions, whether biotic or abiotic.

Over the past several decades, larger and larger datasets have been utilized and increasingly sophisticated methods have been deployed (e.g., procedures to account for sampling and taxonomic biases, model selection using the Akaike information criterion, or morphometric techniques quantifying changes in form). These studies have revealed new patterns and removed old ones, emphasizing how the empirical signature of directionality is affected by biases of different kinds. Just as important has been a growth in the number of patterns that can be documented using different constructs or currencies (e.g., functional, taxonomic, or morphological diversity). Additionally, increasingly refined accounts of potential sources of directionality, whether intrinsic (e.g., developmental bias), extrinsic (e.g., geochemistry, paleoclimatology, or paleoecology) or otherwise (e.g., a principle of probability), have suggested that drivers of directional patterns are far more complicated than was previously assumed, with different sources generating the same pattern or operating in concert or differentially on traits in fossil lineages. However, the implications or broader interpretations (if any) remain largely unexplored, including whether the existence of directional patterns (or lack thereof) and predominance of particular drivers (or lack thereof) bear positively or negatively on traditional concerns about the significance of trends in the history of life, especially if more than “largest-scale” trends are contemplated. Can we identify and characterize innovative paleontological research on the existence, causes, and meaning of directionality in the fossil record based on robust data-driven approaches that reach beyond conventional modes of inquiry?

Potential Questions

• How can we conceptualize and operationalize empirical signatures of directionality innovatively? Should we elaborate traditional macroevolutionary constructs or currencies (e.g., taxonomic diversity) or develop newer ones (e.g., functional diversity)? What about less accessible variables (e.g., biomass/productivity)? What new variables would permit using new or distinctive data sets?

• What variables are insufficiently standardized to permit the detection of directionality? What constructs are heterogeneously operationalized and lead to problematic cross-comparisons? Are signatures of directionality in traits (e.g., size increase) concordant with signatures of directionality for lineages (e.g., differential speciation or extinction)?

• Robust empirical signatures can often be captured by comparing one or more constructs: can new examples of these scenarios be identified (e.g., same construct, such as functional diversity, in different lineages, or different constructs, such as taxonomic and functional diversity, in the same lineage)? How can different drivers and their possible interactions be better distinguished? How should relative strengths of causality be attributed to different drivers?

• Given vulnerability to sampling or taxonomic biases, what signatures might be more prone to false positives? To what degree are signatures impacted by insufficient attention to spatial or temporal resolution? To insufficient taxonomic synonymization or phylogenetic standardization?

• Does the inclusion of neontological data increase or decrease confidence for particular drivers (e.g., comparison of developmental variability with phenotypic variation in the fossil record)? Do specific types of drivers yield “recurrent” empirical signatures, such as increases or decreases for shorter or longer segments of geological time?

• Can the magnitude of trends be preferentially attributable to intrinsic versus extrinsic drivers (including the relative lack of reversals)? Is one type of driver more persistent through spans of geological time? For particular properties (e.g., differential origination versus extinction or frequency of novelty origination)? Do types of drivers play larger or smaller roles under extreme circumstances in the history of life (e.g., mass extinctions) as opposed to “normal” or background circumstances? Where can clear failures of drivers be demonstrated, if at all?

• What larger generalizations (if any) can be gleaned through: (i) comparing and contrasting genuine empirical signatures and/or (ii) removing artifactual signatures? Have any signature types been inadequately explored? Are any larger generalizations possible or are predominant drivers always trait or clade specific? Can the zero-force evolutionary law be empirically confirmed as a key driver of complexity and diversity in life’s history (and at what scale)? Are there deeper aspects of biotic or abiotic organization that structure fossil record trajectories of directionality? Can we draw any conclusions about whether the existence of directional patterns (or lack thereof) and predominance of particular drivers (or lack thereof) bear on traditional concerns about the wider significance of macroevolutionary trends in the history of life?

Instructions

Compelling responses to this research track will prioritize clear, bold and actionable projects related to empirically detecting directionality in the fossil record and discriminating its drivers in the history of life. The aim is to identify and characterize novel conceptions of these ideas for new scientific research that can fruitfully explore the associated phenomena and/or their distinctive features. Some potential respondents may believe that their previous work has already addressed one or more of the overlapping questions posed above. Such individuals are encouraged to apply, providing they address both why such answers have yet to gain broader traction within the relevant scientific communities and how they propose to increase such traction. Successful outcomes will not only fuel increased insight, but garner sufficient attention to change the status quo of scientific thinking on these frontiers.

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