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Euclides
Tuesday, May 11th, 2004, 11:21 PM
Cohort effects in a genetically determined trait: eye colour among US whites


M. D. Grant A1 and D. S. Lauderdale

A1 Department of Family Medicine, Loyola University Chicago Stritch School of Medicine, Maywood, IL, USA


Abstract:

Background: While the inheritance of eye colour is likely polygenic, blue eye colour is thought to follow an inheritance pattern similar to that of a recessive trait. Consequently, age-related differences in the prevalence of blue eye colour would be unanticipated.

Aim: This study explores the finding and explanation for birth cohort differences in the prevalence of blue eye colour in the US white population.

Subjects and methods: Data from the first (1971-1975) and third (1988-1994) US National Health and Nutrition Examination Surveys (NHANES-I and NHANES-III), nationally representative surveys of the US population, were analysed. Trends in eye colour prevalence by birth cohort were analysed together with mortality rates according to eye colour. US census data (1980) were examined to explore cohort differences in ancestry and assortative mating by ancestry.

Results: The prevalence of blue eye colour among non-Hispanic whites in NHANES-III was 57.4% (95% CI: 50.1-64.7) for individuals born between 1899 and 1905 compared to 33.8% (95% CI: 31.3-36.5) for those born between 1936 and 1951. No association was found between survival and eye colour, nor was a cohort effect evident for primary ancestry. However, proportions reporting only one ancestry in census data declined with successive birth cohorts.

Conclusions: A cohort effect in blue eye colour prevalence was found for the US white population. A secular trend of decreasing assortative mating by ancestry is the likely explanation.

Glenlivet
Wednesday, May 12th, 2004, 12:24 AM
The number for blue eyes is very high, like most of Northern Europe. It is important to know how large the sample was.

Graeme
Wednesday, May 19th, 2004, 02:50 PM
Could you post a link to that study.

Nordhammer
Friday, May 21st, 2004, 04:43 AM
A big decrease, indicating the effect of nonNordish immigration and Nords mixing with nonNords.

Results: The prevalence of blue eye colour among non-Hispanic whites in NHANES-III was 57.4% (95% CI: 50.1-64.7) for individuals born between 1899 and 1905 compared to 33.8% (95% CI: 31.3-36.5) for those born between 1936 and 1951.

StrÝbog
Friday, May 21st, 2004, 05:19 AM
Certainly less than 1/2 (and possibly less than 1/3) of white Americans have blue/grey/green eyes.



A big decrease, indicating the effect of nonNordish immigration and Nords mixing with nonNords.


I see a lot of blonde/blue girls of NW European ancestry with black/brown or brown/brown guys also of NW European ancestry, usually Atlantids guys with Nordic or UP women. How do you feel about these pairings? They are intraethnic but still decrease the rate of blue eyes in the population and further dilute the subtypes...

In fact, grouping dark Brits in the "Nordish" scheme for historical or geographic as opposed to genuinely phenotypical reasons has an adverse effect on preservation of the depigmented types, since it encourages mixing between ALL "Nordish" types.

Nordhammer
Friday, May 21st, 2004, 05:30 AM
Certainly less than 1/2 (and possibly less than 1/3) of white Americans have blue/grey/green eyes.

I see a lot of blonde/blue girls of NW European ancestry with black/brown or brown/brown guys also of NW European ancestry, usually Atlantids guys with Nordic or UP women. How do you feel about these pairings? They are intraethnic but still decrease the rate of blue eyes in the population and further dilute the subtypes...

In fact, grouping dark Brits in the "Nordish" scheme for historical or geographic as opposed to genuinely phenotypical reasons has an adverse effect on preservation of the depigmented types, since it encourages mixing between ALL "Nordish" types.

I think people should mate according to their phenotype and ancestry, within the Nordish range. The Nordish concept doesn't encourage mixing between all Nordish types, rather it excludes incompatible types.

Indigenous darker types are fine, they're a stabilized blend and often have lighter people in their ancestry. They are not a threat. Although in general I think the pairing and increased fecundity of lighter types is a good thing. Would you rather a white population get lighter or darker?

StrÝbog
Friday, May 21st, 2004, 05:56 AM
I think people should mate according to their phenotype and ancestry, within the Nordish range. The Nordish concept doesn't encourage mixing between all Nordish types, rather it excludes incompatible types.

Indigenous darker types are fine, they're a stabilized blend and often have lighter people in their ancestry. They are not a threat. Although in general I think the pairing and increased fecundity of lighter types is a good thing. Would you rather a white population get lighter or darker?

That's fine. To me, the Nordish concept is not ideal, but it's obviously far better than the mating patterns we are witnessing right now.

Louky
Wednesday, May 26th, 2004, 02:15 PM
Certainly less than 1/2 (and possibly less than 1/3) of white Americans have blue/grey/green eyes.
Where do you get this? I thought the study was on blue eyes. If what you wrote is true, then I must live in an atypical region of the the US. From my observation, most people around here have light-mixed eyes, as in NE, but pure light eyes are almost as common. It's pure dark eyes that are rare (among Whites).

Dr. Solar Wolff
Thursday, May 27th, 2004, 06:44 AM
The number for blue eyes is very high, like most of Northern Europe. It is important to know how large the sample was.

These are hardly anthropologically or medically trained people doing the survey. Also, there were two surveys, possibly with different people doing the work with possibly different methodology. We don't know from the abstract. What about light-mixed eyes or grey eyes? There is no doubt that non-Nordid immigration has increased in the last generation in the USA.

Also, about 30% of the genes, even in Ireland and Norway are for non-blue eyes, so people with non-blue eyes shouldn't necessarily have to "take a back seat".

Beware of American studies. Most were funded with a political objective.

zombienursestef
Saturday, October 1st, 2005, 06:00 AM
Eye color is determined genetically. Accuracy depends on the whole person genetically. Consider the dark eyed caucasion with a reccesive blue eyed gene to pass down to their children, compared to a double dominant, dark eyed carrier of caucasion decent. Green eyes carries a separate, extra gene entirely. Study should be limited to dark or blue eyes with percentage of carrier types?

Willigut
Sunday, October 2nd, 2005, 02:51 AM
USA distribution of blue eye colour in 1920 thies. Source: "Truman State University" (http://www.eugenicsarchive.org/eugenics/list_topics.pl).
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