Where do Blue Eyes Come From
When I started to research this topic for Science Sunday, I expected to find some evolutionary advantage to blue eyes in northern climates since blue eyes are mostly associated with Siberian Huskies. In humans, blue eyes co-evolved with light skin and blonde hair in northern regions then spread through Europe. In humans lighter skin allows for better synthesis of vitamin D from the sun. This was an advantage in northern regions where sunlight levels are lower. The process works like this: the oil in our skin reacts with sunlight to produce vitamin D which is then absorbed through the skin into the blood stream. In equatorial climates, the sun is intense enough for this process to work even in darker skinned individuals. Dogs produce the same oil on their skin but any vitamin D that is produced is absorbed into their fur. This works okay for cats who spend a lot of time licking their fur, but dogs must get most of their vitamin D from their diet. This was traditionally from meat but more now from manufactured dog food supplemented with vitamin D. So blue eyes did not confer the same evolutionary advantage to dogs as it did to humans.
They did not inherit blue eyes from their predecessor, the wolf, since no wolf species have blue eyes.
A genetic study released in October 2018 looked for the genetic markers associated with eye colour. The study, by Embark Veterinary, looked at the genome of 6000 dogs and compared some 200,000 genetic markers. The team found a mutation on chromosome 19 that was strongly correlated with subjects reported to have blue eyes. The gene, called ALX4, has not been associated with eye colour in humans or mice, meaning that the mutation is completely new to researchers.
So we now know where blue eyes come from, but we don't know why. Siberians are not the only breed to sport blue eyes. Other breeds include:
The answer to the prevalence of blue eyes may be more mundane than evolutionary advantage. John Hawks of the University of Wisconsin-Madison speaking about the prevalence of blue eyes in humans said “This gene does something good for people. It makes them have more kids.” So just as blonde haired blue eyed humans breed more often the evidence suggests that blue eyes in dogs was also selected for simply because of their piercing allure.
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