Dog is man’s best friend, but the length and nature of the relationship between humans and dogs is a combative and controversial field, "more than any other subject in prehistory," according to one researcher.

Researchers think that early services of working dogs and their hunting prowess was an important factor in humans out-competing Neanderthals and eventually becoming farmers and herders.

Charles Darwin began the speculation in 1868 when he asked whether dogs might have evolved from a single species or from an unusual mating as between a wolf and a jackal. In 1907, Francis Galton suggested that it began when humans snatched some wolf pups, brought them back to camp and raised them as pets.

In the 1990s, genetic analysis determined that dogs share 99.9 percent of their DNA with gray wolves, solving this bit of the puzzle. But even with the genetic lineages established, the exact when and where of the transition from wolf to dog remain a mystery.

Part of the problem of pinning down a precise date is in defining exactly what "dog" means. One might expect intermediate stages showing gradual changes over time as canines from diverse areas interbred along trade routes between Europe and China via the Middle East.

One example is a skull from the Goyet cave in Belgium, which radiometric dating determined to be 32,000 years old. The original analysis deemed it to be from wolf, but measurements of the skull made in 2009 suggested it was more dog than wolf, making it much older than the oldest known dog remains.

Many scientists argued that the Goyet skull could merely be a strange-looking wolf rather than an ancient dog. Alternatively, it could be an early dog that was not in the lineage of modern dogs.

Most experts now think that dogs domesticated themselves by hanging around camp scrounging for scraps. The development of human civilization made a new niche available for somebody to move into, and concomitant adaptations in canines’ ability to digest starches allowed them to eat grains and tubers along with their human counterparts.

Dogs have as many as four times the number of copies of the gene for amylase as wolves do. That protein starts the breakdown of starch in the intestine.

Dogs were likely preselected to scavenge off people in the same way that dogs today are preselected to play fetch and snuggle.

It did not hurt that dogs have an innate social structure that made it easier for them to integrate themselves into human family groups.

The ability of dogs to read humans is legendary. They instinctually know what is going on using careful observation and integration of their keen senses. They can hear emotion in the human voice and respond both sympathetically and empathetically. Recent studies show the increase in oxytocin levels in human-dog relationships is similar to the bonding between mother and child, and between lovers.

It seems safe to say that we have co-evolved with our canine companions, which explains why dog is man’s best friend and vice versa. We grew up together.

Richard Brill is a professor of science at Honolulu Community College. His column runs on the first and third Friday of the month. Email questions and comments to brill@hawaii.edu.