Thoughts on the origin of dogs. 1.

1.    

Jean-Baptist Lamarck seems to be the first scientist to suggest dogs were descended from wolves. In his 1809 Zoological Philosophy he wrote, “No doubt a single, original race, closely resembling the wolf if indeed it was not actually the wolf, was at some period reduced by man to domestication.”

Dog ancestry has been debated ever since Lamarck’s comments and a variety of hypotheses have been proposed and tested in various ways.

Olsen (1985) suggested hominids and wolves have had a relationship that started sometime between 500,000 and 200,000 YPB. He wrote,

“One of the earliest known associations of Canis lupus with hominids (Homo erectus pekinensis) is from the fossil site at Zhoukoudian, located about 42 kilometers southwest of Beijing… Although this association of hominids and wolves at this early period does not imply in any way either taming or early domestication it does place both genera of animals in contemporary association that apparently continued until such time that these events did occur.”

In fact evidence of hominids and canids living in proximity dates to 810,000-760,000 YBP in Spain (Garcia and Arsuaga, 1999); and to about 521,000 YBP at Boxgrove, England. Garcia and Arsuage consider the Boxgrove canid to be Canis mosbachensis. Thus, Olsen’s comment is further supported – the two genera, Canis and Homo have a long relationship, even if it was only sharing the same landscape as competitors – they were part of the same fauna and destined to interact. Keep in mind that members of a fauna adapt to each other, the adaptations may be obvious or subtle.

Stories of dog domestication are numerous, each with their own twists and wrinkles added by the authors, for now I will summarize the domestication event stories by saying. Humans picked up wolf cubs raised them and the wolves adopted their human family. Wolves were selected for tameness and they quickly morphed over generations into the ancestor of the domestic dog of today.

This has become a “just so story” that is relatively well accepted in the minds of the general public and probably most people who study dogs. Just so stories are dangerous because they become dogma until they are replaced with an alternative story based upon a changing paradigm as more contrary evidence accumulates to suggest an alternative scenario.

Most of the popular literature and scientific work affirm Lamarck’s proposal, the grey wolf (Canis lupus) is the ancestor of the domestic dog. Evidence for a close relationship between grey wolves and dogs is quite substantial using morphology, genetics, and the fact that dogs and wolves hybridize. Below is a phylogeny for canids from Linblad et al. (2005), they used a  

“…a high-quality draft genome sequence of the domestic dog (Canis familiaris), together with a dense map of single nucleotide polymorphisms (SNPs) across breeds. The dog is of particular interest because it provides important evolutionary information and because existing breeds show great phenotypic diversity for morphological, physiological and behavioural traits….”

There are a large number of phylogenies in the literature and most of them show a similar arrangement when it comes to dogs and the grey wolf. The arrangement is as sister species – not ancestor-descendant. A general principle of cladistics suggests that when one species separates into two, the ancestral species “dies,” meaning it no longer exists. In its place are the two sister species. Following this idea, Canis lupus and Canis familaris are sister species not ancestor and decedent.  The sister species relationship is supported in numerous studies and should not be controversial.

However, only extant species are represented in the tree. There are likely several to many extinct members of the genus Canis not in the tree because their DNA is not available. If they could be added, the tree would have a different topography. As more fossil Canis are found it is likely ancient DNA will be extracted from them and added to the tree. When this occurs the sister relationship between C. lupus and C. familaris is likely to change.

Our knowledge of canids is still incomplete. Leonard and colleagues (2007) examined remains of 56 ancient wolves from the permafrost near Fairbanks, Alaska and found a continuous population from 12,500 YBP to beyond the capacity of radiocarbon (about 58,000 years) to resolve a date for them. Only a single wolf was dated after the 12,500 year mark, at 7,647 YBP. The older wolf remains showed wider palates with larger carnassial teeth suggesting they had a greater bite force. Their teeth also showed greater degrees of wear suggesting that they were specialized for killing and consuming large prey or habitually scavenging on exceptionally large prey – the megafauna. Leonard and colleagues obtained ancient DNA from 20 of these wolves from the late Pleistocene of eastern Beringia and recovered a haplotype that was not shared with any existing wolf population. The Pleistocene gray wolf was quiet distinct from the modern gray wolf. However, three wolves from the Ukraine and one from Altia (Russia) dated between 30,000 and 28,000 YBP shared the same haplotype as the Fairbanks remains  ―suggesting the Pleistocene Gray Wolf was widely distributed in the Northern Hemisphere from at least 50,000 YBP to about 12,500 YBP. These wolves lived north of the ice sheets. A nitrogen isotope analysis of the bones showed the Pleistocene Gray Wolf preyed and scavenged on mammoth, bison, musk ox and caribou.

The lack of overlap between modern wolves and the Pleistocene wolves is striking and suggests the ancient wolves became extinct and were not ancestral to the modern wolf. As the megafauna herbivores disappeared so did their predators, the Pleistocene Gray Wolf was one of them.

While I don’t claim to have the ultimate answer to dog origins the following seem likely and obvious:

      1) Dogs shared an ancestor with a wolf – but not the extant gray wolf.
2) Dogs are primarily scavengers, but they can act as predators.
3) The social structure found in dogs is not as rigid as that found in extant gray wolves.
4) Dogs and wolves do hybridize, but wolves often show aggression towards domestic dogs, reducing the likelihood of hybridization under natural conditions.
5) The geographic point of origin is likely somewhere in Eurasia as opposed to Africa or North America – but African Canis familaris do show substantial genetic diversity
6) The dog or its ancestor was pre-adapted for interacting with humans.
7)  Humans (and in the broad sense, hominins) have a long history of interacting with dogs (and probably their ancestor), thus dog-human interactions, and dogs as a species predate agriculture.

References

Freedman AH, Gronau I, Schweizer RM, Ortega-Del Vecchyo D, Han E, et al. (2014) Genome Sequencing Highlights the Dynamic Early History of Dogs. PLoS Genetics 10(1): e1004016. doi:10.1371/journal.pgen.1004016

Garcı́a, N., & Arsuaga, J. L. (1999). Carnivores from the Early Pleistocene hominid-bearing Trinchera Dolina 6 (Sierra de Atapuerca, Spain). Journal of Human Evolution, 37(3), 415-430.

Lamarck, JB 1809. Zoological Philosophy: An Exposition with Regard to the Natural History of Animals, vol. 1, Dentu, Paris, France.

Leonard, J. A. C. Vilia, K. Fox-Dobbs, P. L. Koch, R. K. Wayne, and B. V. Valkenburgh. 2007. Megafaunal extinctions and the disappearance of a specialized wolf ecomorph. Current Biology 17:1146-1150.

Lindblad-Toh, K., et al.  2005. Genome sequence, comparative analysis and haplotype structure of the domestic dog." Nature 438.7069: 803-819.

Olsen, SJ. 1985. The Origins of the Domestic Dog, the Fossil Record. University of Arizona Press.