Very rarely is an entire family group of hominins buried and fossilized at the same time. It is even rarer for paleoanthropologists to discover such an assemblage. Fortunately for science but unfortunately for the hominins, caves occasionally collapsed on entire social groups.
At a site known as El Sidrón in Spain, excavations have been ongoing since 2000. To date, 12 Neandertals have been discovered in a context that points to a single geological event, circa 49,000 years ago. A group of 12 Neandertals is consistent with previous estimates of around 10 individuals per group. At least six adults, three adolescents and four younger individuals were buried at once, most likely during a storm. The cold conditions of the cave system and immediate burial of the remains not only preserved the bones well, but were also ideal for DNA.
The remains were sexed based on both morphology and DNA analysis. After sex was determined, anthropologists identified the different Neandertal lineages based on mitochondrial DNA. Several of the adults were found to be male, and the other three female. It was discovered that all three males belong to the same matrilineal group, while each respective female has a different haplotype. When compared to modern Europeans, the authors noted that there is significantly less genetic diversity within the mitochondrial genome.
These results strongly imply that Neandertals exhibited patrilocal mating behavior. Females were the ones who would have changed family groups, not males. This type of insight into an extinct species is unique, thanks to the quality of DNA preservation available at El Sidrón.
Another interesting point of discussion in the study relates to Neandertal interbirth interval. One of the females was linked by DNA to two of the younger individuals, approximately several years apart in age. If the anthropologists are correct about the relationship, this puts the interbirth interval for Homo neanderthalensis at a value similar to hunter-gatherer groups today. This data, if replicated with other Neandertal individuals, could eventually dispel differential reproduction as a potential cause for Neandertal disappearance.
Knowing about Neandertal group dynamics could provide crucial clues as to why they went extinct. Future analysis of the remains recovered at El Sidrón will no doubt give more insights into our closest extinct relatives, and perhaps even why Homo sapiens flourished and Neandertals declined.
By Matthew Magnani
Lalueza-Fox, C., et al. (2011). “Genetic evidence for patrilocal mating behavior among Neandertal groups.” PNAS . January 4, vol. 108 no. 1 250-253.