Monday, April 29, 2013

reopening the chicken/egg controversy

My online friend Malcolm Pollack of the most excellent Waka Waka Waka thought he had settled the "Which came first—the chicken or the egg?" controversy long ago. "Which came first? The egg. Move on," wrote Malcolm. Why? Malcolm explained:

How does speciation occur? Is it by some creature starting its life as one species and ending up as another? Obviously not. New forms of life arise through mutation, through the imperfect transfer of genetic information from parent to child. So in this example something that was not-quite-a-chicken laid an egg containing the world’s first chicken.

I was happy with this explanation for a long time. But in trolling the archives of Lee Farrand's blog (and you'll recall that Lee is a biologist), I found this:

When referring to a situation in which the original cause out of two likely explanations is unknown, many people like to use the old chestnut:

"Which came first, the chicken or the egg?"

This is an example of metacircularity and is designed to be unanswerable. But the biological answer in terms of evolution is: the chicken.

The reason for this is [that] the egg is part of the chicken's reproductive strategy. If you traced the chicken's ancestors back in time throughout evolutionary history, you'd find that the eggs were more watery, from the amphibian lineage that we all share. If you went back further still, to simpler and primordial ancestors of the chicken, which were aquatic plankton, you'd find that eventually there was a point where sexual reproduction began. Before this time, the modus operandi of all reproductivity was binary fission[, i.e.,] one cell dividing into two - in which case, there were no eggs to speak of. Eggs arose after the first organisms developed meiosis, the ability to divide chromosomes between gamete cells.

So the answer to this question is that the chicken came first, although the ancient 'chickens' we are referring to are quite different to the chickens of today.

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



pitchfest said...

Malcolm has an excellent point. But we are answering from slightly different angles. He is referring to the particular species (I assume) of the domestic chicken, and at which point it spontaneously came into being.
I was taking a broader view, of organisms and eggs in general: The egg-layer vs the egg, in which case it was egg-layers first.
However, even with Malcolm's perspective, there is still a technical issue. He is correct that speciation most likely occurred in the progeny of the "pre-chicken mother", barring spontaneous mutation in the gonads of an adult. However, I took a course on avian reproductive biology and it actually turns out that the egg shell itself forms much later, in the final hour before laying. The single-celled oocyte that arises from fertilization and would represent the "fetal chicken" exists prior to any ovomucoid protein or shell deposition around it. So, in that sense, the chicken organism exists prior to the formation of the egg.

Kevin Kim said...

Not sure whether the above is actually in English, but thanks for the response!

John said...

Does life begin in the eggshell or after hatching?

Elisson said...

Q: Which came first, the chicken or the egg?

A: The rooster.

pitchfest said...

Well if we look at hatching, it's a little more simple. The question would be: is a chicken still a chicken before it has left the eggshell? The answer is yes, because we can culture chicken embryos much like IVF, in dishes (called surrogate eggshells, although purely plastic). And these individuals can go on to mate and produce viable offspring. So the hatching itself is not really the crux of the issue. Perhaps it would be the question: can an egg with a chicken inside spontaneously appear without having being laid? Well, yes, if you have a religion that believes in the virgin birth of a chicken savior.

Kevin Kim said...


I suspect that John meant his question facetiously, as a parodic riff off the "Does life begin at conception?" and "When is a fetus a person?" issues in the abortion debates.

Lee Farrand said...

Oh I see. So that's why I never get invited to dinner parties....