Which came first? The chicken or the blue egg?

After I cleared up everyones confusion on why chicken gonads are lopsided, and why we have white chickens, I thought I would tackle another one of lifes great mysteries.

Admit it. Youve wondered where the hell blue chicken eggs come from.

Source: http://www.lespetitesgourmettes.com/recipes/gorgeous/

I ‘get’ brown eggs. I ‘get’ white, kinda. BUT WHERE THE HELL DID BLUE COME FROM?

‘Well, you see when a chicken lays an egg mid-flight on a bright, sunny day, predators on the ground have a harder time seeing the blue egg…’


No, seriously, whats up with blue chicken eggs?

Turns out it is a side-effect of wayward ERV expression that is not disasterous enough to lead to negative selection! Phenotypic diversity due to mutations!

An EAV-HP Insertion in 5′ Flanking Region of SLCO1B3 Causes Blue Eggshell in the Chicken

Endogenous Retrovirus EAV-HP Linked to Blue Egg Phenotype in Mapuche Fowl

In that first paper, scientists in China made the initial observation: wayward activity of a bird ERV lead to over-expression of SLCO1B3 in chicken uteruses (uterii?), which leads to the transport of bile salt, which leads to blue chicken eggs!


Since these were Chinese chickens laying blue eggs, what about other chickens in Europe? North and South America?

In the second paper, researchers investigated why those other chickens laid blue eggs. Was it the same ERV at the same location leading to the same phenotype due to common descent? OR was it a different ERV at a similar location leading to the same phenotype? OR was it a totally different phenomenon?

The South American and European chickens have the same ERV insertion at the same site, which enhanced SLCO1B3 expression. The Chinese chickens had a different ERV inserted in a different site, but it lead to the exact same phenotype due to again, enhanced SLCO1B3 expression.

So which came first? The chicken or the blue egg?

The chicken.


A retroviral infection of an egg or sperm lead to the formation of a chicken (white egg) with the appropriate ERV insertion. That chicken subsequently laid blue eggs. This happened once to give rise to the Chinese blue-egged chickens, and then again to give rise to the South American/European blue-egged chickens.





  1. #1 Sannica
    September 11, 2013

    Hah, love it!

  2. #2 JustaTech
    September 12, 2013

    Here’s a better question: There are blue eggs and blue flowers and blue feathers, but no blue fur. Why not blue fur?

  3. #3 Sheri
    September 12, 2013

    Cool info!

  4. #4 Anon
    September 13, 2013

    JustaTech: Blue feathers (and eyes) come from diffracted/scattered light (not a pigment)[1], but fur gets its color from melanin. The underlying structure of a hair doesn’t provide a method for light to diffract and scatter to yield blue fur, even if totally unpigmented.

    1: http://www.smithsonianmag.com/science-nature/Why-Are-Some-Feathers-Blue.html

  5. #5 Rada
    <a href="http://symmed.ru/">Neurologist</a>
    September 15, 2013

    It is good that the chicken itself is not blue.

  6. #6 Timothy Allman
    September 15, 2013

    Commenting here because I don’t see how to send a direct message. Thought you might like to see this


  7. #7 ERV
    September 15, 2013

    Ha! HAHA! Thanks! (for the link and the comment– I put a contact page up in the right side-bar– my contact info must have disappeared during some revamp of the site!)

New comments have been disabled.