Canine companions possess significantly less voluminous brains compared to their ancestral wolf counterparts. A recent investigation spearheaded by French researchers has aimed to delineate the temporal framework for the commencement of this cranial shrinkage, a phenomenon often associated with the domestication process.
The findings suggest that this reduction was already substantially in progress a minimum of 5,000 years ago, coinciding with humanity’s transition to established, agrarian communities.
Cranial tissue is notoriously fragile and rarely preserved in fossil records; however, skeletal remains are far more durable. The internal volume of the cranium, also referred to as the neurocranial cavity, serves as a conventional proxy for estimating brain volume, given that the brain typically occupies this space.
Thomas Cucchi, a zooarchaeologist affiliated with France’s National Museum of Natural History, along with his associates, employed CT scanning technology to quantify the cranial cavity volumes of 22 ancient wolves and dogs unearthed from archaeological sites in Belgium and France. To ensure a rigorous and equitable comparison, the same methodology was applied to 163 extant specimens of both modern dogs and wolves included in the research.
For every canid specimen under examination, the researchers also computed the ratio of the brain cavity’s volume to the animal’s overall skull length. This crucial step enabled them to ascertain brain size relative to the animal’s somatic dimensions – for instance, a brain volume considered typical for a diminutive dog would be deemed exceptionally small for a considerably larger canine.
Within the dataset were two specimens identified as ‘protodogs.’ One, discovered in Belgium and dating back approximately 35,000 years, and the other from France, dating to roughly 15,000 years ago, exhibited relative brain sizes comparable to those of wolves from the Pleistocene, Neolithic, and modern epochs.
These protodogs are believed to represent the nascent stages of the human-canine association, marking their divergence from wolves, although both groups remain classified within the same species even today. Critically, they predate the widespread adoption of agriculture, a pivotal epoch in the evolutionary trajectory of humankind and, potentially, canines as well.
By approximately 5,000 years ago, the cranial capacity of dogs had undergone a profound transformation, markedly differing from that of their wild progenitors.
Canine specimens from the Late Neolithic period displayed brains that were roughly half the size of those belonging to contemporary wolves. These ancient dogs possessed relative brain sizes that bore resemblance to those observed in modern terrier breeds and miniature canine varieties, such as pugs, Chihuahuas, and Pekingese.
The study’s authors posit that this observation could signify the advent of early behavioral selection, wherein humans actively fostered and propagated traits in dogs that aligned with their own needs and interests.
“This pronounced reduction in brain volume during the Neolithic era offers significant insights into their potential roles, such as providing early warnings against threats within settlements, alongside other functions like scavenging—a readily available source of sustenance—or assisting in hunts,” the researchers articulate.
While currently speculative, the researchers propose that a diminished brain volume may have necessitated a redistribution of neural tissue: a reduction in the proportional size of the cortex, which is implicated in perception, cognition, and attention, and an expansion of the subcortex, the region responsible for fundamental physiological processes such as homeostasis, motor control, and emotional processing.
This proposed neurological shift, they theorize, could have substantially altered canine temperaments in ways that proved advantageous to Late Neolithic human populations in Western Europe.
For instance, canines exhibiting heightened anxiety and wariness could have served effectively as alarm systems for burgeoning settlements within nascent agrarian societies. Conversely, these very characteristics might have rendered the dogs more challenging to train.
Nonetheless, extensive further investigation is imperative to fully comprehend the actual characteristics of these ancient dogs. Cranial volume does not invariably correlate with cognitive capacity, and the intricate interplay of these traits with cultural development will necessitate the accumulation of more extensive archaeological evidence.
This particular finding stands in marked contrast to the formidable flock-guarding canids, which are considered among the earliest established dog ‘breeds.’
“To further document the temporal origins and the cultural contexts surrounding these evolutionary changes, additional specimens of Mesolithic and Neolithic dogs from across the European continent require thorough examination,” the authors concede.
