Creationists are probably used to ignoring yet another example of a 'non-existent' fossil showing intermediate or 'transitional' features between an ancestral and a descendant species. If not, they should be since these turn up with monotonous regularity.
A little more unusual are those examples of another of their 'non-existent' feature of biological evolution - new structure.
So, today's news gives creationists another fact to ignore and proclaim not to be there - domestic dogs have a structure which is not found in their wolf ancestors. Moreover, the mechanism by which it evolved is easy to understand in terms of how the environment selected for the ability this new structure gives dogs.
The new structure is a muscle, the levator anguli oculi medialis (LAOM), on the inner margin of the eye that enables domestic dogs to raise their eyebrows, making them more appealing to humans. Dogs can appeal to humans by simply making their eyes look larger in a facial changes that makes them more puppy-like and friendly.
This discovery was made by a team led by Juliane Kaminski of the University of Portsmouth, Hampshire, UK and is published open access today in PNAS:
Significance
Dogs were shaped during the course of domestication both in their behavior and in their anatomical features. Here we show that domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. A muscle responsible for raising the inner eyebrow intensely is uniformly present in dogs but not in wolves. Behavioral data show that dogs also produce the eyebrow movement significantly more often and with higher intensity than wolves do, with highest-intensity movements produced exclusively by dogs. Interestingly, this movement increases paedomorphism and resembles an expression humans produce when sad, so its production in dogs may trigger a nurturing response. We hypothesize that dogs’ expressive eyebrows are the result of selection based on humans’ preferences.
Abstract
Domestication shaped wolves into dogs and transformed both their behavior and their anatomy. Here we show that, in only 33,000 y, domestication transformed the facial muscle anatomy of dogs specifically for facial communication with humans. Based on dissections of dog and wolf heads, we show that the levator anguli oculi medialis, a muscle responsible for raising the inner eyebrow intensely, is uniformly present in dogs but not in wolves. Behavioral data, collected from dogs and wolves, show that dogs produce the eyebrow movement significantly more often and with higher intensity than wolves do, with highest-intensity movements produced exclusively by dogs. Interestingly, this movement increases paedomorphism and resembles an expression that humans produce when sad, so its production in dogs may trigger a nurturing response in humans. We hypothesize that dogs with expressive eyebrows had a selection advantage and that “puppy dog eyes” are the result of selection based on humans’ preferences.
Kaminski, J., Waller, B. M., Diogo, R., Hartstone-Rose, A., & Burrows, A. M. (2019).
Evolution of facial muscle anatomy in dogs.
Proceedings of the National Academy of Sciences, 201820653. https://doi.org/10.1073/pnas.1820653116
Copyright 2019 the Author(s). Published by PNAS.
Open access.
Reprinted under a Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
This work followed on from research in 2013 by Juliane Kaminski which looked at reasons why people choose particular dogs over other for adoption from a shelter. Analysing video tapes of interaction between the dogs and strangers, they found that dogs that made the eye movement this LAOM muscle makes possible most often were most likely to be adopted.
The new research shows that of the specimens of different types of domestic dogs examined, the only one not to have this muscle was the Siberian husky, which is one of the domestic dogs most closely related to the ancestral wolves. No wolves had this muscle. Instead, they had a small tendon partially connected to another muscle.
Clearly, what has happened over the evolutionary history of domestic dogs is that humans have done what they were observed to do in the dog shelter and preferred dogs that could do the appealing little trick of turning on puppy eyes. The more they were able to do it the more likely they were to succeed under the selection pressure of human preference.
Nothing more than the selective pressure in the environment of evolving domestic digs has favoured mutations that enabled dogs to appeal to humans, not even necessarily consciously on the part of either dogs or humans. The next step will be to identify the genes responsible for this new structure and showing how they arose by mutation.
This is a clear example of a new structure evolving by Darwinian evolution and a clear refutation of a basic creationist dogma. Tweet
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