by Kenneth W. Krause.
[Notable New Media]
Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer. Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes frequently to Skeptic as well. He can be contracted at firstname.lastname@example.org.
Despite biologists’ great interest and effort, a detailed history of the domestic dog’s evolution has remained elusive. Scientists have estimated the date of divergence between dogs (Canis lupus familiaris) and wolves (or wolf-like canids) at anywhere between 10,000 and 32,000 years ago. Similarly, using maternally transmitted mitochondrial DNA and haplotype analyses, researchers have proposed a number of possible regions as the dog’s birthplace, including Europe and the Middle East.
But a new study on dog origins suggests a more definitive answer. An international team of biologists led by geneticist Ya-Ping Zhang recently collected the whole genome sequences of 58 canids, including 12 grey wolves from Europe, 11 dogs from southern East Asia, 12 dogs from northern East Asia, 4 dogs from Nigeria, and 19 diverse dog breeds from across the Old World and the Americas (Wang et al. 2015).
Following examination of these sequences, Zhang’s team discovered that the highest genetic diversity—a strong signal of species origination—occurred among dogs indigenous to southern East Asia. Other populations demonstrated a progressive gradient in ancestry away from wolves beginning in southern East Asia. These findings, the group noted, tend to corroborate earlier work based on mitochondrial DNA and paternally transmitted Y-chromosomal DNA.
As for the timing of dog-wolf divergence and the subsequent dispersal of dogs globally, Zhang and colleagues used various genomic techniques that, in their estimation, revealed a two-step process. First, dog and wolf populations began to separate about 33,000 years ago in southern East Asia. Then, around 15,000 years ago, dog subgroups began to radiate westward, reaching the Middle East, Africa, and finally Europe about 10,000 years ago. Meanwhile, one Asian population backtracked to northern China, they suggest, mixed with northern East Asian dogs, and eventually made its way to the New World.
So how and when were dogs actually domesticated? A number of non-exclusive evolutionary theories of varying plausibility have been advanced over the years. According to Hungarian ethologist Adam Miklosi, however, only a handful of these theories are consistent with the scientific evidence. In his new book, Miklosi specifies that early humans might have plucked canid cubs from their dens, for example, selecting only those with the most affiliative temperaments. Or perhaps humans and canids co-evolved, each species by exerting selective pressures on the other. Group selection may have played a role as well, if early dogs somehow boosted the survival rate and reproductive fitness of some human groups over that of others (Miklosi 2015).
Zhang’s group, however, favors the scenario in which an ancient dog-wolf split comprised the first step in both the domestication of wolves and evolution of domestic dogs. Humans and the ancestors of dogs probably shared an ecological niche in southern East Asia, they argue, that offered refuge to both species during the last glacial period, which peaked between 26,500 and 19,000 years ago. The long process of domestication may have began with a group of wolves that became “loosely associated and scavenged with” humans before undergoing “self-domestication”—that is, “waves of selection for phenotypes [in other words, behaviors and physical traits] that gradually favored stronger bonding with humans.”
Miklosi, Adam. 2015. Dog behavior, evolution, and cognition (second edition). Oxford, UK: Oxford University Press.
Wang, G., W. Zhai, H. Yang, et al. 2015. Out of southern East Asia: the natural history of domestic dogs across the world. Cell Research 15 December 2015; doi:10.1038/cr.2015.147.