Sunday, January 27, 2013

Ray Coppinger guest-blogs about starch digestion mutation in dogs

On January 23, 2013, a groundbreaking study was published by a team of canine geneticists from the University of Uppsala, Sweden, announcing they have identified key mutations in three genetic regions that allowed the traditionally carnivorous wolf, or pre-curser to dogs depending on your position,  to subsist on a starch-rich diet.  (Read my post in Bark magazine.) Here, canine expert Ray Coppinger comments on the paper.
Ray Coppinger at Wolf Park, Indiana, USA

Evolutionary biologist Ray Coppinger, professor emeritus from the School of Cognitive Science, Hampshire College, Massachusettes, has raced, bred and studied dogs all over the world for decades.  Ray and his wife, Lorna, developed the modern and controversial theory of how dogs evolved by natural selection, in contrast to the more consensus view that people intentionally domesticated dogs by artificial selection.  The Coppingers argue that dogs, shaped by the environment they find themselves in, evolved as one of the all time most successful scavengers. The Coppingers theorize that over time, humans adopted these wild dogs, continuing to shape them further into diverse forms.

Dog scavengers at Mexico City dump
Photo by Virgiania Broitman

Although the journal article doesn't say when the mutations occurred, the authors suggest that the adaptation was surely useful for opportunistic animals that were scavenging waste near ancient farming communities. 
First wolf tasting her new grain based diet?
Does it support the village dog domestication theory?  Professor Coppinger comments below.


"Dogs and wolves are the same species.  They are subspecies of each other.  Sub species simply means they are polymorphic for many characteristics. And THAT simply means that they vary in the shape of particular characteristics. For example, dogs and wolves differ in size, shape, faces, color, and behavior.  
Dog skull (above) compared to wolf skull
Jawbone of dog and wolf
As the muzzle foreshortens in the dog,
the teeth crowd together.  

The eyes become rounder and move forward on the skull.
Last week an article in the Journal Nature showed brilliantly that dogs and wolves differ in another trait, their ability to digest starch. Wolves can digest starch, but dogs are better at it.  “Better” means they can do it more efficiently.  What that means is that in a niche full of starch, dogs would out-compete wolves.  All niches are limited, says Darwin, and more individuals are born than the niche can support.  Natural selection will favor the most efficient individuals.  
An efficient niche-filler
Ethiopian Village Dog
Photo courtesy Alessia Ortolani
The Nature paper concludes dogs are better adapted to living in the grain-rich environment created by humans. When did dogs get those genes for digesting grains?  
Village dogs feeding at dump site in Ethiopia.
Photo courtesy Alessia Ortolani
How such a mutation becomes dominant in a population is a complicated process, but certainly isn't instantaneous.  The assumption would be that "wolves" were already occupying the dump nicne and then came the mutation.  So the initial population didn't have the "new and improved" genes for digesting starch.  When did the new and improved system evolve? We don't know, nor do the authors suggest a time line.  Certainly not right at the beginning, and it could have come only a few hundred years ago. Or although unlikely, even with the invention of dog food.  More study is needed. 
Some of us who support the village dog domestication theory would like to think that it happened in the Neolith period, after humans developed their sedentary life based on growing grain crops. We would also like to believe that the adaptation of the wild species – call them wolves – into dogs was the result of natural selection for being tame around humans and being able to digest their starchy waste products. 
Village dogs at Mexico City dump
Photo courtesy of Ray Coppinger
Does the Nature paper suggest how dogs evolved?  I wish it did because I am sure it would support the Village Dog hypothesis.  But it also doesn't support the possibility that dogs could have evolved before the Neolith, by artificial selection, meaning people taking wild wolf pups from the den, taming and domesticating them. Some people like me and my students who actually have taken wolves from the den and laboriously tamed them, think this latter hypothesis is silly, but the Nature paper doesn’t rule out that possibility."
Read more about the dog's adaptation to a starch-rich diet at these links:

  • The genomic signature of dog domestication reveals adaptation to a starch-rich diet, Journal Nature, published on-line, January 23, 2013.
  • The Bark blog
  • Author Mark Derr comments on the study.
  • This link will take you to a description of a 2010 lecture about dogs at the Mexico City dump by Ray Coppinger: The Mexico City dump, an island paradise of dogs, a fresh view of an old relationship

What do you think?  Comment here or go to my post at Bark and leave a comment there.

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