SIMPLE ANTHROPOLOGY OF BLUE-EYED PEOPLE

Watching patients and families come through my office for the past several decades has allowed me to formulate some thoughts about blue eye color and physical characteristics of humans who have them. Thinking about where blue-eyed people came from geographically, it seems a high

 percentage of them came from northern places where average temperatures are colder, such as Ireland and England in my case, and Scandinavia and other northern European countries. In

 those regions it would make sense that there is adaptation to cold, just as it seems that people with darker skin and darker eyes seem to tolerate warmer geographical areas better and even prefer them. One of the adaptations that I have observed is the ability of blue-eyed babies to preferentially send blood to their core when they are exposed to decreases in room temperature, as in the first few hours after birth or taking their clothes off for a feeding or an exam. Their hands and feet become purplish, they may get blueness around the mouth and often their skin mottles.. Continuing to circulate blood to the skin only makes one colder. When

 sleeping in the winter, they may wake in the morning with "freezing" hands, but the rest of their body is toasty warm. In warmer ambient temperatures, blue-eyed toddlers often get quite red in the summer heat or when running around and often wake from naps in the summer drenched with sweat. Just as  they circulate less blood to the skin when cooler, they send more blood to the skin when hot to help lower body temperature. We often say babies "run hot" or adults will say, "I always run hot". 

It appears to me that blue-eyed people in general have warmer bodies than dark-eyed people. Blue-eyed people are more comfortable living where it is cooler and dark-eyed people living where it is warmer like southern California. I have observed in the hospital that most of the babies who seem to be having trouble maintaining temperature are dark-eyed babies, and I have wondered if they are not having a normal dark-eyed lower temperature. 

Living in a cold place, people wear more clothes and are exposed the sun and air less, whereas dark-eyed people living in a warm place do not wear as much clothing to cover up the skin. This appears to result in blue-end people having more sensitive skin because we accumulate less melanin in our skin. Another result of being warm and living in a warmer place is that blue-eyed people tend to sweat more because of being too warm. The combination of more sensitive skin and sweating too much leads to dry skin and the issues that go with it. In addition, we tend to dress babies in one layer more than adults and this is probably one layer too much for blue-eyed babies. Blue-eyed children and adults will as a result have to spend more time moisturizing skin and choosing soaps and skin care products which do not tend to dry the skin.

Blue-eyed children and adults are also much more sensitive to light in the eyes. When I first  moved to southern California, I truly thought there was something wrong with my eyes because I was almost blinded by stepping out of buildings into the sunlight. I see the same reaction in the office when I use the

 ophthalmoscope to check eyes on an exam. Blue-eyed children start squinting before I even get close to their eyes and often their eyes water. An interesting thing is that some brown-eyed children have the same reaction and then I look and either mom or dad has blue eyes, so brown-eyed children who have blue-eyed ancestors can have the same reaction. 

Most babies will have their permanent eye color by 6 months, but I have seen babies who finally changed around 2 years old. And it turns out that eye color changes even later in life in a certain percentage of the population. As a general rule, babies eyes can change from blue to brown, but brown eyed babies never change to blue eyes.

A very detailed article on Eye colour: portals into pigmentation genes and

ancestry can be found at:

http://www.biosci.ohio-state.edu/~pfuerst/courses/eeobmg640/reading1eyecolor.pdf

In January 2008 information appeared in Scienceblog and in an article from the Wellcome Trust regarding the origin of blue eyes:

All blue-eyed humans have common ancestor

http://www.scienceblog.com/cms/print/15361

By BJS

Created 01/30/2008 - 16:14

  New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen has tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today. “Originally, we all had brown eyes”, said Professor Eiberg from the Department of Cellular and Molecular Medicine. “But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which literally “turned off” the ability to produce brown eyes”. The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The “switch”, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue. The switch’s effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour – a condition known as albinism. 

Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.” Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production. 

Professor Eiberg and his team examined mitochondrial DNA and compared the eye colour of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye colour. Nature shuffles our genes 

The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.” 

Blue eyes and red hair

http://www.wellcome.ac.uk/Professional-resources/Education-resources/Big-Picture/All-issues/How-We-Look/Articles/WTD041629.htm

 

The genetic basis of blue eyes and the classic Celtic look - red hair and pale skin - has been discovered. Both are linked to the production of melanin.

Although eye colour used to be considered a simple Mendelian recessive trait, the genetics of human eye colour are surprisingly complex. Eye colour depends on pigments in the iris (principally eumelanin), and many subtle shades exist. A key factor seems to be variation in the OCA2 gene, which is mutated in a form of albinism.

This is not just of cosmetic interest. Variation in OCA2 also affects freckling and skin pigmentation and is a risk factor for skin cancer.

Surprisingly, blue eyes result not from changes in OCA2 but in a nearby gene, HERC2, which regulates OCA2. In January 2008, several groups identified HERC2 mutations - in fact, all present-day examples of blue eyes may have their origins in a single change that occurred 6-10 000 years ago, during the expansion of humans in the Stone Age.

Why did it persist - blue eyes seem to offer no selective advantage? Perhaps it was chance. Or perhaps blue eyes were particularly attractive to Stone Age women…

Low melanin levels is also a feature of the classic ‘Celtic’ look - red hair and pale skin. It is a feature of people with two inactive alleles of the gene for the melanocortin 1 receptor (MC1R), who need to be particularly careful about sun exposure, as they are more vulnerable to UV radiation and at increased risk of skin cancer.

MC1R codes for a receptor found on pigment cells, melanocytes, which make skin pigments - eumelanin and the lighter phaeomelanin. Variation in MC1R affects the ratio of eu- to phaeomelanin and hence the depth of colour in the skin. Redheads produce almost no eumelanin.

Interestingly, analysis of two Neanderthal remains revealed variation in their MC1R gene sequence, suggesting that Neanderthals too showed variation in hair and skin colour pigmentation.