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NOT PROGRAMMED. "General explanations for organismal senescence are varied and contentious, and the idea that iteroparous senescence is “programmed” is not the majority view." https://lnkd.in/ecP3KMX View in LinkedIn

SO ENDS this topic of mass extinctions. It is a remarkable history of boom and bust events in life’s history, from great abundance to hanging by a thread. What is evident, is that it is hard to snuff life out, even in the face of cataclysmic events. Some life forms will survive. Even when you look at the growth and survival of seedlings, there is an evident force to survive at all costs in any conditions. Life is a fiercely determined force. View in LinkedIn

COMPLEX AND UNPREDICTABLE. “The evolutionary response to mass extinction is slow on human time scales, difficult to predict owing to the contingencies of postextinction conditions including the identity and evolutionary dynamics of the survivors, and geographically heterogeneous.” http://www.pnas.org/content/98/10/5393.full/Donnie) View in LinkedIn

FORCE OF CHANGE. “Extinction itself promotes biotic interchange. Asymmetries in ancient biotic interchange generally appear to reflect geographic differences in extinction intensity. The end-Cretaceous extinction shows, however, that although biotic interchanges pervade the postextinction world, simple linear relationships can break down to produce unexpected source-sink patterns.“ http://www.pnas.org/content/98/10/5393.full/Donnie) View in LinkedIn

NO GUARANTEES. “Survivorship during mass extinctions need not be closely related to many aspects of biological success as measured during “background” times.” http://www.pnas.org/content/98/10/5393.full/Donnie) View in LinkedIn

ONGOING EVENTS. “Mass extinctions happen. The fossil record provides ample evidence that even the more widespread and species-rich clades, ecosystems, and biogeographic provinces are not infinitely resilient.” http://www.pnas.org/content/98/10/5393.full/Donnie) View in LinkedIn

CONCLUSION. “I would not go far wrong in saying that the most dramatic evolutionary effects of mass extinctions can be epitomized in just four words: they remove successful incumbents.” http://www.pnas.org/content/98/10/5393.full/Donnie) View in LinkedIn

BOOM TIME. “The significant increase in standing diversity began approximately 500 million years ago. During the Ordovician, marine family diversity tripled and those clades that came to dominate the next 250 million years radiated.” (See Figure 1). https://lnkd.in/eVq28Qh View in LinkedIn

DIVERSIFICATION CONTINUED. “Marine family diversity tripled and within clade diversity increases occurred at the genus and species levels. The Ordovician radiation established the Paleozoic Evolutionary Fauna; those taxa which dominated the marine realm for the next 250 million years. Community structure dramatically increased in complexity.” https://lnkd.in/eVq28Qh View in LinkedIn

LATER COMPLEXIFICATION. “There was a major diversification known as the Ordovician Radiation, in the period immediately following the Cambrian. This event is unique in taxonomic, ecologic and biogeographic aspects. While all of the phyla but one were established during the Cambrian explosion, taxonomic increases during the Ordovician were manifest at lower taxonomic levels although ordinal level diversity doubled.” https://lnkd.in/eVq28Qh View in LinkedIn