Climate and the demise of the Neandertals

From "Time for the Middle to Upper Paleolithic transition in Europe"

by Wil Roebroeks; Faculty of Archaeology, Leiden University, P.O. Box 9515, 2300RA Leiden, The Netherlands

http://dx.doi.org.ezproxy.lib.utexas.edu/10.1016/j.jhevol.2008.08.008

Ice core studies have taught us that the time span of Middle and Upper Paleolithic was punctuated by rapid climatic transitions on timescales of centuries or even decades (Adams et al., 1999). Vegetation responses to such rapid fluctuations must have varied on small scales among sites and regions, according to the differences in initial environmental conditions, local and regional species pool, and the climate events concerned, and the same applies to faunal elements, including Neandertals and modern humans. Various authors have suggested that such climatic fluctuations were instrumental in the disappearance of the Neandertals, one of the latest climatic hypotheses having been presented by Mellars (2006) who suggests that their final demise may have coincided with the sudden onset of the much colder and drier conditions of the Heinrich Event 4. However, extremes of temperatures reached during this period were not exceptional, and had been experienced in earlier glacial-interglacial cycles survived by Neandertals, where the extremes of OIS 4 and 6 led to abandonment of the northern parts of Europe, as did the most extreme parts of OIS 2, for modern humans (e.g., Roebroeks et al., 1992). Recently Tzedakis et al. (2007) have also made the point that climate change was probably not the key factor here, as before 28 ka ¹⁴C BP (i.e., according to most of the papers in this volume long after their demise) Neandertals would have faced a pattern of climatic fluctuations that they had been surviving for at least 100,000 years already.

History of Simulating Evolution

Wessen-Simulating-human-origin-evo.pdf

Simulating Human Origins and Evolution by Ken Wessen (2005) p 12:

Raup et al. (1973) studied the generation of species lineages by modelling speciation as an equilibrium process of random lineage branching. All lineages stem from a common ancestor, and may continue in time, become extinct, or produce a new lineage by branching, with a probability based on the difference between the existing diversity and a predetermined equilibrium value. An algorithm for the automatic identification of clades was included, allowing study of the taxonomy of the resulting phylogeny. The simulations produced quite a variety of clade shapes, which were then compared with actual clades for the Reptilia. An important fact demonstrated by this work is that differences in evolutionary pattern do not necessarily imply an inherent difference in the associated taxonomic groups: simulated groups evolving under identical constraints can behave very differently. Sepkoski and Kendrick (1993) used a similar model to simulate phylogenies. Employing exponential, logistic and mass-extinction diversification profiles, the resulting phylogenies were degraded in various ways (to model the effects of fossilisation, for example) and the information content remaining was analysed with respect to the ‘true’ phylogeny. Both these models can be generalised to allow the study of higher taxa, e.g. genus, family, etc. Nee et al. (1994) also used a similar approach to study the reconstruction of phylogenies, looking particularly at the role of lineages that become extinct.

Rarity, specialization and extinction in primates

Rarity, specialization and extinction in primates by A. H. Harcourt, S. A. Coppeto, S. A. Parks 2002

DOI: 10.1046/j.1365-2699.2002.00685.x

Main conclusions: The most commonly demonstrated traits of susceptibility to extinction are those of high resource use, slow recovery rate, and specialization. Yet, while rarity is an inevitable precursor to extinction, specialization is the only trait found to correlate with rarity in this study. We cannot explain this apparent contradiction.

If nothing goes extinct without first being rare, why does rarity in primates correlate with only one of the sets of traits that have been shown to be associated with susceptibility to extinction in primates, not all of them, i.e. with only specialization, and not also with high resource requirements and slow population recovery rate? One of the most important issues an evolutionary biologist can address is, surely, the biology of extinction. If we are puzzled about a link between rarity and extinction, if we do not know what makes a taxon prone to extinction, we leave unexplained the course of evolution. We know what went extinct and when, but we do not know why. This analysis, with its huge amount of variation unexplained, and its surprising result, indicates that even for one of the better known mammalian orders, we are far from a complete understanding of the causes and consequences of rarity and extinction, and therefore of the processes of evolution.