Some human and dog mothers will compete with their offspring under certain circumstances, and now a new study presents evidence that such infighting likely compelled the earliest dogs to leave their selfish moms for a life with people.
If the theory, outlined in the journal Royal Society Open Science, is validated with even more evidence, it could help to explain the origins of dog domestication and how some canines so willingly elected to live with people instead of with their own kind.
The study also adds to the growing body of evidence that it was no coincidence that the first large ancestral populations of dogs emerged as humans began to farm and settle down.
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"What we would like to suggest is this: human camps would be a source of rich resources for ancestral dog populations," senior author Anindita Bhadra of the Indian Institute of Science Education and Research told Discovery News. "Since richer resources can induce higher conflict, it can eventually lead to individuals defecting from their groups to follow the resource hubs, i.e., humans."
Bhadra, lead author Manabi Paul, and colleagues Sreejani Sen Majumder and Anjan Nandi studied the interactions of feral Indian dog mothers and pups as different qualities of food were made available to them.
When low-quality biscuits were offered, the mothers tended to share with their pups and no conflicts ensued. When protein-rich meat was offered, however, the dog moms seemed to forget their motherly ways. The feral dog moms would growl at their pups, and even grab meat from the pups' mouths. The dejected, hungry pups were left whimpering.
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Human settlements, on the other hand, left behind a lot of food refuse that the ancestral dogs could have accessed. There is evidence that the earliest farmers intentionally fed these dogs too, making following people instead of selfish moms all the more attractive.
This switch might have occurred when the young dogs were 8-9 weeks old, the authors suggest. This is when juveniles - incapable of discriminating between different types of food and being too small to do much damage to prey - forage and hunt with adults, usually including mom.
Bhadra said that as feral dogs become adults, "they can stay with the mother, but might also leave the group, which usually consists of about three to six individuals. The mother can also leave, at times, especially during the mating season." She added that incest is common, with mother-son and father-daughter matings happening frequently.
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As for why the dog moms become so selfish, Bhadra said, "We feel that the mothers just tend to grab the best resources when available."
She continued, "The dogs have retained a strong preference for meat in spite of adapting to a scavenging lifestyle in a carbohydrate rich environment, and they seem to use a simple rule of thumb to sequester maximum animal protein - if it smells like meat, eat it."
When there is less food available, and it is of poor quality, the mothers will tend to be more generous with their pups, even stopping to feed them acquired food. This is probably just because the mom's motivation to compete is low, and therefore does not interfere with her altruistic instincts, the authors suggest.
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Humans show similar behavior, prior research has found. A classic example is when a family shares moderate resources and then a rich relative with a will dies. Suddenly a caring relative might turn competitive, hoping to gain the greater riches.
Bhadra described another example, where "parents and offspring have very different interests in the mate of the offspring, leading to trouble in the family."
So dogs share some social behaviors with humans, but much about man's best friend still remains a mystery.
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Ádám Miklósi, head of the Department of Ethology at Eötvös University, told Discovery News that the new study "is very timely, as we need to understand the success of free-ranging dogs at so many part of the world."
"Free-ranging dogs' mothers seem to be sensitive to the food supply of their environment," he added. "They decrease investment in the puppies if the environment provides richer resources. The flexibility of maternal behavior may explain why free-ranging dogs reach such large densities, despite high mortality rates."