Here is a sweet treat for dog lovers, anthropologists and evolutionary biologists, though not so much for creationists.
An open access paper published very recently in Royal Society Open Science not only sheds light on domestic dog and modern human co-evolution but illustrates an important principle in evolutionary biology: evolution will occur in the presence of a change in the environment with little or no change in the information in the genome. It also shows how gene duplication can play an enormous role in the evolution of a species.
Three years ago a Swedish team discovered that domestic dogs carry multiple copies of the gene Amy2B, which is associated with the production of the pancreatic digestive enzyme amylase, which digests starch, turning it into glucose sugar. Humans also have many more copies of this gene than do carnivores. This was highly suggestive that dogs may have been much easier to domesticate because they were able to digest the higher starch content found in the human diet and so could share our food, or at least the scraps.
Now, A team of researchers from France, Sweden and Romania believe they have shown that the increase in copy numbers, which appears to enhance the ability to digest starch, occurred in both species at about the same time and about the time that humans began to switch from a hunter-gathering to an agriculture-based culture in Eurasia.
Extant dog and wolf DNA indicates that dog domestication was accompanied by the selection of a series of duplications on the Amy2B gene coding for pancreatic amylase. In this study, we used a palaeogenetic approach to investigate the timing and expansion of the Amy2B gene in the ancient dog populations of Western and Eastern Europe and Southwest Asia. Quantitative polymerase chain reaction was used to estimate the copy numbers of this gene for 13 ancient dog samples, dated to between 15 000 and 4000 years before present (cal. BP). This evidenced an increase of Amy2B copies in ancient dogs from as early as the 7th millennium cal. BP in Southeastern Europe. We found that the gene expansion was not fixed across all dogs within this early farming context, with ancient dogs bearing between 2 and 20 diploid copies of the gene. The results also suggested that selection for the increased Amy2B copy number started 7000 years cal. BP, at the latest. This expansion reflects a local adaptation that allowed dogs to thrive on a starch rich diet, especially within early farming societies, and suggests a biocultural coevolution of dog genes and human culture.
Morgane Ollivier, Anne Tresset, Fabiola Bastian, Laetitia Lagoutte, Erik Axelsson, Maja-Louise Arendt, Adrian Bălăşescu, Marjan Marshour, Mikhail V. Sablin, Laure Salanova, Jean-Denis Vigne, Christophe Hitte, Catherine Hänni
Amy2B copy number variation reveals starch diet adaptations in ancient European dogs
R. Soc. open sci. 2016 3 160449; DOI: 10.1098/rsos.160449. Published 9 November 2016
© 2016 The Authors.
Published by the Royal Society under the terms of the Creative Commons Attribution License (CC BY 4.0)
The principle illustrated here is how an environmental change, in this case an increase in the amount of starch in the food supply of the domestic dogs created the selection pressure for an improved ability to make use of that starch to be selected for. The increased ability was of course produced by the increase in copy number of the gene Amy2B, which itself was a mere repeated gene duplication. The increase in information and complexity was of course minimal since it was simply a repeat of existing information, not new information as such.
But the meaning of that information was that starch became a food for domestic dogs, unlike the situation with wild dogs and wolves. It also illustrates well how two species can become linked in a coevolutionary, symbiotic relationship. The driver of this was the discovery of staple food plants which could be cultivated to first supplement, then replace, the food previously hunted and gathered from the wild.
Domestic dogs, which had probably progressed from scavenging on the human spoil tips and maybe guarding the encampments, to assistants in hunts, were now there to be bred and adapted to help with herding and guarding the other domestic animals and other chores, the whole system depending on alliances of genomes between domesticated plants and animals and humans.
In the case of this adaptation by dogs to the starch in the human diet there were all the classical features of evolution so loathed by creationists. There was mutation which was not only not deleterious but highly beneficial and involved no loss of information, not even a change in information, and minimal increase in complexity. There was a clear change in the genome over time and selection pressure which inevitably brought about that change by entirely natural means and without conscious interference. And the entire process increased the degree of separation from the wild wolf from which domestic dogs had diverged.
And the genetic evidence maps onto the archaeological and palaeoanthropological evidence.
Perhaps there is a creationist who isn't still too over-excited by their success in getting their preferred racist, misogynist apostle of hate, Donald Trump, elected as US president to explain why this example isn't an example of evolution by natural selection.
Incidentally, did anyone notice the evidence from this paper of the Theory of Evolution by natural selection is a theory in crisis about to be overthrown and replaced by magic? Me neither. It seems to have formed the fundamental scientific principle by which the facts are explained.
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