Wednesday, June 02, 2010

Statistically Probable Thought #2

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 because 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 ie. 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.

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Daniel Larsson said...

Hi Lee,

This is a question I've been given quite A LOT of though... -_-;

At first I was totally in agreement with your above reasoning. But this question has many levels.

Basically, why could not the chicken be the reproductive strategy of the egg!? Think of it, shouldn't the haploid cell precede the diploid cell? Bacteria are haploid. The reason why you'd be diploid would obviously be the fusion of two cells (i.e. sex!).

With best regards from Sweden,

Lee Farrand said...

Hi Danne danne!

You have a great point.

However, if you think about it solely from a (#)ploid centric-view, it's hard to extend the argument further. For example, many species of bacteria have more than one chromosome copy (up to four) and also retroviruses like Human T-lymphotrophic virus are diploid. So polyploidy itself may be a goal of sexual reproduction, but it isn't necessarily exclusive.
Also, it really gets down to which is the wagon and which is the cart. We could define 'species of egg' that hatch egg-propagators, which is funny. But you can raise chicken cells in media, and if you had the technology, could remove the egg-forming genes and they would still grow. A chicken could be rendered incapable of making an egg (like a navel orange), but all unfertilized eggs are incapable of becoming anything (they're technically non-life). If you think about unfertilized human ovaries using humans as a means to propagate, it becomes more obscure. So you go back down the ancestral chain and at the point of the first meiosis, it was a 'chicken', or multicellular organism that did it, not a single celled egg.

Anonymous said...

I'm glad you have finally explained this chicken and egg situation. The very next time I am asked this question, I'm going to quote you, that is if I can remember what you said. You said it was the...

Anonymous said...

However, I don't think I can buy it.
You're just saying the chicken's ancestors came before the egg.
But dinosaurs were producing eggs before chickens evolved.

On the other hand, if the question were
which came first, the chicken or the chicken's egg,
the answer has to be neither,
they evolved simultaneously.

It's a catch 22 situation,
a bit like when you leave school and apply for a job
and experience is one of the qualifications.
You can't get one without the other.

Roboseyo said...

OK. So what's your biologically-based description of the sound of one hand clapping? Meditators worldwide want to know, now that you've stolen one of their koans.

Lee Farrand said...

Bill, yes you're right about dinosaurs. Chickens directly evolved from reptiles, which makes them 'living dinosaurs' in a way. What I'm saying is that if you narrowed it down to the crucial instant in time, you can't have had chicken + egg simultaneously, because they're like phases of the moon, it had to start at one particular phase. And the starting 'phase' must have been a replicating animal producing an egg, not the appearance of an egg, because it would have had to have been fertilized prior, by some sort of 'chicken'. But I see your point.

And Rob, that's a little abstract for technical accuracy. But I can offer you one of my favourite biological definitions: of the word 'kiss'
"The anatomical juxtaposition of two orbicular muscles in a state of contraction."

2tonone said...

As for your anatomic definition of "kiss", is it correct to call it anatomic when you are dealing with two separate organisms? I think "physical" is more appropriate in this case than "anatomical".
It's not easy to leave a comment here since I began blogging just a few days ago and am not used to the way things work here on google.^^

Lee Farrand said...

Physical is used when referring to fundamental structure, whereas anatomical refers to the structure of living things. Whether one or more organisms is not really relevant. You could call it the physical juxtaposition of gelatinous soft tissue structures, but it just doesn't have the same ring to it.