Sunday, May 20, 2012

Homo sapiens sapiens: A species that has gone to the dogs?

Pat Shipman has a provocative new comment in American Scientist suggesting that  the energetic benefits of hunting with dogs gave anatomically modern humans (AMH) a significant advantage over Neandertals, and led, as some newspaper headlines have suggested, to the "extinction" of Neandertals. (Neandertals and other premodern humans didn't actually go extinct. Their genes live on in descendant Eurasian populations. It is clear, however, that AMH were demographically more successful than their chinless contemporaries.)

If so, then the unique, co-evolutionary relationship humans have with dogs could be a critical component of behavioral modernity, like art and ornament, composite tools, or fishing. The question remains, why did this relationship develop when and where it did? Other "modern" behaviors occur only sporadically prior to 50k years ago, and are not correlated to biological changes. For example, art was created by both premodern and AMH populations, and many populations of both show no evidence for art. If a domestic relationship with dogs was a critical aspect of AMH adaptation, why did it occur after 50k years ago, and not before? What would have prevented Neandertals or other premodern humans from forming the same relationship with canids?

Shipman's article is thought-provoking, although speculative (as she acknowledges), and I hope will inspire further investigation. Her suggestion relies heavily on evidence for early dog domestication in Europe, but evidence for the location and timing of dog domestication is hard to pin down. Genetic studies have been contradictory, suggesting East Asian or Middle Eastern origins for dogs, and failing to identify a clear time of origin, partly because of on-going gene flow with wolf populations (Pang et al. 2009; von Holdt et al. 2010). 

The archaeological data is somewhat stronger, with evidence of dog-like characteristics in some canids as early as 33k years ago (Ovodov et al. 2011), but still not conclusive. Germonpré et al. (2011) argued for dog domestication 26k years ago at Předmostí, in the Czech Republic. Their work is thorough and well-documented, but the site produced only a few specimens that they argue to be dog, and an MNI of over 100 canids, most of which are wolf. The large number of wolves is problematic. Finding a few domestic dogs among so many wolves is like finding a few flakes in a pile of naturally broken rocks: are we sure the (arguably) domesticated finds aren't within the expected natural variation? Such variation must have existed within wolves, in order to be selected for during the process of domestication. The remains were clearly modified by humans post mortem, so I'm not convinced that  Germonpré et al. are wrong, I'm just not convinced they're right, particularly given the small number of dog remains that have been found from the Paleolithic, and the complete lack of dog remains dating to the critical time period of Neandertal/AMH overlap.

Shipman argues that the use of canid teeth for ornaments suggests they were not seen as prey, but red deer teeth are commonly used as ornaments in Upper Paleolithic Europe, and they clearly were prey. Similarly, equating the absence of art depicting canids to the absence of art depicting human figures is an interesting contention, but not, in itself, very strong evidence for a special relationship with the artists. 

One of the most interesting aspects of Shipman's argument is her documentation of the significant energetic savings that dogs could have provided AMH hunters. The evidence she cites comes from modern ethnographic work, of course, which may or may not apply to mammoth hunting (the main prey species found at Předmostí). Shipman notes that moose hunting yields are increased by the use of hunting dogs who corner prey and hold them until their human partners can arrive. But mammoths are much bigger than moose. Could dogs hold them at bay? Shipman also cites evidence that prey encounter rates are greater for hunters who use dogs, but these studies mostly focus on small-game hunting. A dog's tracking ability may always be useful, but encounter rates for mammoths would have been less affected by vegetation cover than is the case for small prey in tropical environments. Mammoths don't get lost in the underbrush!

I'd be the last person to argue that human/animal relationships are less than crucial to understanding human ecology, despite my reservations about Shipman's proposal. Although Paleolithic dog domestication is well outside my own research focus, I hope to hear more about this hypothesis, and see more work done on the relevant faunas. She's raised a lot of very interesting questions!


Germonpré, M., M. Lázničková-Galetová and M. Sablin
2012 Palaeolithic dog skulls at the Gravettian Předmostí site, the Czech Republic. Journal of Archaeological Science 39:84–202.

2011 A 33,000-Year-Old Incipient Dog from the Altai Mountains of Siberia: Evidence of the Earliest Domestication Disrupted by the Last Glacial Maximum. PLoS ONE 

Pang J-F, Kluetsch C, Zou X-J, Zhang A, Luo L-Y, et al. 
2009 mtDNA data indicate a single origin for dogs south of Yangtze River, less than 16,300 years ago, from numerous wolves. Molecular Biology and Evolution 26: 2849–2864 

vonHoldt BM, Pollinger JP, Lohmueller KE, Han E, Parker HG, et al. 
2010 Genome-wide SNP and haplotype analyses reveal a rich history underlying dog domestication. Nature 464: 898–903. 

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