Although only the abstract to this paper is free to access, this story has received extensive coverage elsewhere over the past few days, and is of particular interest because there is apparently a strong case for suggesting that Neanderthals may have been consigned to extinction from around 40,000 bp when their numbers dwindled at first before speeding fast into terminal decline. (AMH had arrived in Europe some time after 50,000 bp and by 40,000 bp were presumably around in sufficient numbers to possibly cause what has been described elsewhere as ‘extinction by competitive exclusion‘.) This is because recent research suggests that Neanderthals never attained the population density necessary to ensure their survival over the long term in the face of competition for resources, in part mitigated by climate swings evidenced by the waxing and waning of glacial events during the Neanderthals’ 200,000 – 300,000 year long sojourn in Palaeolithic Eurasia.
Here’s the abstract:
Analysis of Neandertal DNA holds great potential for investigating the population history of this group of hominins, but progress has been limited due to the rarity of samples and damaged state of the DNA. We present a method of targeted ancient DNA sequence retrieval that greatly reduces sample destruction and sequencing demands and use this method to reconstruct the complete mitochondrial DNA (mtDNA) genomes of five Neandertals from across their geographic range. We find that mtDNA genetic diversity in Neandertals that lived 38,000 to 70,000 years ago was approximately one-third of that in contemporary modern humans. Together with analyses of mtDNA protein evolution, these data suggest that the long-term effective population size of Neandertals was smaller than that of modern humans and extant great apes.
This paper is commented upon extensively at the Spittoon, where AnneH notes that a more efficient and accurate method of sampling ancient DNA (aDNA), using a method by the name of Primer Extension Capture (PEC) was deployed. This allowed the authors of this study to analyse 5 Neanderthals, as described here:
This new study, also led by Max Planck Institute scientists, centers around a novel method for finding and extracting that elusive aDNA from Neanderthal remains. The study took advantage of a new kind of aDNA extraction process, called Primer Extension Capture (PEC). This technique has many advantages over the others, primarily because it allows the aDNA to be completely isolated from all the other molecular junk that can accumulate over time.
This yields highly accurate results with much less effort. So instead of simply using this technique on one Neanderthal individual, they analyzed five. The remains they chose had been excavated from a variety of locations, from Croatia to Germany to Spain and Russia. Most of the remains were between 35,000 and 40,000 years old, which is very close to when Neanderthals were believed to have disappeared from most of their range. They also examined Neanderthal remains from Russia that dated to between 60,000 and 70,000 years old.
After successfully extracting and analyzing the DNA of these remains, the researchers came to a few startling conclusions. First, the level of genetic diversity among the samples was exceedingly low. In fact, the amount of genetic diversity of the Neanderthal samples was less than one-third the diversity we see in modern humans today. For example, two of the samples — one from Croatia and the other from Germany — had identical mtDNA genomes. For two individuals living nearly 1,000 miles apart, this is quite unusual; unless there wasn’t much variation in mtDNA in the first place.
The authors of this report think this genetic homogeneity means that there were far fewer Neanderthals living in Europe and western Asia than they’d previously thought. Based on their analysis of the five individuals, the they estimated that the total population size of Neanderthals in Europe 35,000 years ago may have had as few as 3,500 females (because mtDNA is passed down maternally, it cannot be used to estimate male population size).
I’m not sure what the figure of 3,500 female Neanderthals at 35,000 bp implies for the total population, but assuming a roughly equal number of males, and say around 3,000 juveniles, a population numbering around 10,000 might not be too far off the mark.
Of course, the question of population density throughout the various eras of the Upper Palaeolithic, from the Aurignacian to the Magdalenian, is currently open, and on that note I’d like to point readers towards Leherensuge, where Luis has compiled a lengthy and detailed post, ‘How Many People Lived in Paleolithic Europe?, addressing this very problem.
image from National Geographic article : DNA-Based Neanderthal Face Unveiled
1. Targeted Retrieval and Analysis of Five Neandertal mtDNA Genomes by Adrian W. Briggs, Jeffrey M. Good, Richard E. Green, Johannes Krause, Tomislav Maricic, Udo Stenzel, Carles Lalueza-Fox, Pavao Rudan, Dejana Brajkovic, Zeljko Kucan, Ivan Gusic, Ralf Schmitz, Vladimir B. Doronichev, Liubov V. Golovanova, Marco de la Rasilla, Javier Fortea, Antonio Rosas, Svante Pääbo
Science 17 July 2009: Vol. 325. no. 5938, pp. 318 – 321 DOI: 10.1126/science.1174462
2. Neanderthal Extinction by Competitive Exclusion by William E. Banks, Francesco d’Errico, A. Townsend Peterson, Masa Kageyama, Adriana Sima, Maria-Fernanda Sánchez-Goñi
PLoS ONE 3(12): e3972. doi:10.1371/journal.pone.0003972