FIVE PALEOBIOLOGICAL LAWS NEEDED TO UNDERSTAND THE EVOLUTION OF THE LIVING BIOTA: TRYING TO GET BIOLOGISTS TO APPRECIATE THE PERVASIVENESS OF EXTINCTION AND ITS IMPLICATIONS

With the ever-increasing ease of conducting large-scale molecular phylogenetic studies, biologists are more than ever probing the deep-time history, that is, the macroevolutionary dynamics, of the living biota. However, the fact that biologists only have data from living species sometimes leads them to make conclusions that are at odds with facts well established from the fossil record. Thus, for example, zero or very low extinction rates are often reported, and when biologists do not see a signature of the end-Cretaceous mass extinction in their phylogenies they sometimes erroneously conclude that the extinction was un-important to their group.

In an attempt to capture the attention of biological community, and to establish the baseline of paleontological understanding that should be a prerequisite for study of the living biota, I recently wrote a paper in Nature Ecology and Evolution, entitled “Five paleobiological laws needed to understand the evolution of the living biota”. My argument is as follows:

The foundations of several disciplines can be expressed as simple quantitative laws, for example, Newton’s laws or the laws of thermodynamics. Here I present five laws derived from fossil data that describe the relationships among species extinc­tion and longevity, species richness, origination rates, extinction rates and diversification. These statements of our paleobiological knowledge constitute a dimension largely hidden from view when studying the living biota, which are nonetheless crucial to the study of evolution and ecology even for groups with poor or non-existent fossil records.

These laws encapsulate: the critical fact of extinction; that species are typically geologically short-lived, and thus that the number of extinct species typically dwarfs the number of living species; that extinction and origination rates typically have similar magnitudes; and, that significant extinction makes it difficult to infer much about a clade’s early history or its current diversity dynamics from the liv­ing biota alone. Although important strides are being made by biologists to integrate these core paleontological findings into our analysis of the living biota, this knowledge needs to be incorporated more widely if we are to understand their evolutionary dynamics.