Throughout Earth's life history, biodiversity has experienced rapid development and dramatic extinction. We know this at least partially through the fossil record of marine invertebrates that have been left behind since the Cambrian period. Remarkably, extreme events of diversification and extinction occur more frequently than a typical Gaussian distribution would predict. Instead of the typical bell-shaped curve, the fossil record shows a fat tail distribution with extreme outlier events that are more likely than expected.
While scientists had long known this unusual pattern in the fossil record, they had trouble explaining it. Many random processes that occur over a long period of large sampling, from processes that produce school grades to highs below a population, converge on the common Gaussian distribution. "It's a very reasonable standard maintenance," says Andy Rominger, Omidyar Fellow of the Santa Fe Institute. Why does the fossil record not show this pattern?
In a new article that was published in Science Advances Rominger and his colleagues Miguel Fuentes (University of San Sebastián, Chile) and Pablo Marquet (Pontifical Catholic University) Chile have a new approach to Coping with this question. Rather than attempting to describe only variations in biodiversity across all types of organisms, they also consider variations within groups or groups of organisms that share a common lineage.
"Within a lineage of closely related organisms, there should be a conserved evolutionary dynamics that can change between different lineages," says Rominger. That is, within clades, related organisms usually find an effective adaptation strategy and never stray too far. But between these clad-specific fitness peaks lie valleys of metaphorically uninhabited space. "It turned out that just relying on this simple idea with a very simple mathematics, the patterns in the fossil record were described very well."
This simple math is a tool that Fuentes used in 2009 to describe another system with an unusual expression. Fat tail distribution: the stock market. With the help of superstatistics ̵
"In biology, we also see these crashes and explosions in terms of biodiversity," says Rominger. "We were wondering if Fuente's elegant approach could also describe the evolutionary dynamics that we see in the fossil record."
The team writes that their success opens new research directions to better understand the evolutionary processes that lead to both stable extinction rates and speciation at the level of order and family, as well as disruptions that allow the emergence of new life forms.
Well-established theories about patterns in evolution could be wrong
"The non-equilibrium development of volatility at emergence and extinction explains the variations in Phanerozoic biodiversity with fat tails" Science Advances (2019). DOI: 10.1126 / sciadv.aat0122, https://advances.sciencemag.org/content/5/6/eaat0122
A New Normal: Study Explains Universal Pattern in Fossil Stock (2019, June 26)
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