Which Came First, the Chicken or the Egg?

If chick­ens must hatch out of chicken eggs, how could there ever be a first chicken?

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The egg. This ques­tion is less “philo­soph­i­cal” than you might think…


This clas­sic sci­en­tific co­nun­drum has been used in a few ways, down the long years since Charles Dar­win caused all that trou­ble with his “mon­key book”.

Among those who dis­pute the re­al­ity of evo­lu­tion, it’s used to il­lus­trate the prob­lem of the “first cause”. If ev­ery an­i­mal is de­scended from an ear­lier an­i­mal… how did the whole thing start? That’s abio­gen­e­sis, and it doesn’t just break the rules of how our bio­sphere works right now, it breaks our def­i­ni­tion of life it­self.

Life is tricky to de­fine. For now, we de­scribe life as a self­sus­tain­ing, self­con­tained group­ing of one or more cells, which were gen­er­ated by other, ear­lier cells. From the mer­est bac­te­ria to the blue whale, all life has cells, of one kind or another.

Also cru­cial to the def­i­ni­tion is this idea that all cells have ancestor cells, and they go on to cre­ate new cells them­selves. Most of the time, cells just di­vide into (al­most) per­fect copies, ei­ther to re­pair dam­age or to in­crease the to­tal num­ber of cells in – ie grow ­ the or­gan­ism of which they are part. But ev­ery now and then, two very spe­cial cells come to­gether to cre­ate a new, sep­a­rate, self­con­tained or­gan­ism that can go off into the en­vi­ron­ment and, in the case of the chicken, mur­der penny­lizards.

This is of course the essence of sex­ual re­pro­duc­tion. Cells com­bine ge­netic ma­te­rial to cre­ate novel new forms, to beat those fiendish cell­hi­jack­ing viruses and all the other nas­ties that ex­ploit the way our cells work.

Re­peat this process of re­pro­duc­tion bil­lions of times over mil­lions of years, and var­i­ous copy­ing er­rors, ran­dom changes, even the oc­ca­sional cos­mic ray, cause the or­gan­isms to change and, well, evolve.

The prob­lem of course is in iden­ti­fy­ing when a crea­ture stops be­ing a di­nosaur and starts be­ing a bird. Evo­lu­tion­ary sci­en­tists

know there isn’t a

spe­cific day when Species 1 ends and Species 2 takes over. No hairy Homo

erec­tus sud­denly gave birth to a weirdly bald and in­tel­li­gent Homo sapi­ens. It hap­pens over time. Ex­tremely long pe­ri­ods of time.

Crit­ics of evo­lu­tion like to use the ex­am­ple of the chicken and the egg though, be­cause that ex­tra step – birds are “born” on one day, then “hatch” on a dif­fer­ent day – adds ex­tra con­fu­sion. If a proto- chicken lays an egg that hatches into a chicken… was that a proto- chicken egg, or was it a chicken egg?

If they’re be­ing par­tic­u­larly bel­liger­ent, these crit­ics will point out that the in­ter­nal ma­chin­ery re­quired to build an egg is very com­plex, so how could a thing-that-wasn’t-a- chicken pos­si­bly in­clude the right ma­chin­ery in­side it to make a chicken egg?

And this is where the evo­lu­tion­ists step in and try – again – to ex­plain that the bird we call a “chicken” didn’t just sud­denly pop out of a di­nosaur egg or some­thing. It has a bird ancestor which al­ready laid eggs. And be­fore that, eggs were used by di­nosaurs of course, and even ear­lier, by am­phib­ians too.

So ob­vi­ously, “the egg” as a tool for help­ing baby chick­ens de­velop to a size large enough so they can sur­vive when they fi­nally hatch, came first.

But ah, say the crit­ics. We’re not ask­ing if the chicken’s an­ces­tors laid eggs. We’re ask­ing how an an­i­mal that needs to de­velop in an egg could ever come out of an an­i­mal that wasn’t the same species.

One day, a bird we now recog­nise as a chicken, had to be born. There had to be a “first chicken”. But if chick­ens can only hatch out of chicken eggs, how did this hap­pen? How could a, let’s call it a ne­an­der chicken, lay a chicken egg?

To an­swer this, it’s help­ful to re­alise there’s no such thing as a chicken.

Oh fine, se­man­ti­cally of course there are chick­ens. My mother has some. But in a bi­o­log­i­cal sense, this idea of or­gan­is­ing an­i­mals into dis­crete species and say­ing “that an­i­mal there is a griz­zly bear, and that one there is a red kan­ga­roo” is very hu­man, and na­ture doesn’t re­ally pay that much at­ten­tion to it.

What each of us are, in an evo­lu­tion­ary sense, is the or­gan­ism that has been con­structed by a set of genes. Our genes pro­vide the fun­da­men­tal in­struc­tions for what we look like (though our en­vi­ron­ment af­fects the fine de­tails, of course).

If you look only at genes over time, it’s not ex­actly straight­for­ward to tell where one species gives way to another. A mil­lion gen­er­a­tions of a horse-like crea­ture might show a slow loss of one par­tic­u­lar set of genes, while a mu­ta­tion else­where slowly be­comes dom­i­nant and gives the horse­like crea­ture, say, hooves.

There’s no point in time where a horse with no hooves popped out a foal and said “Look at this freak’s feet!” If you had a time ma­chine and made mul­ti­ple stops, say ev­ery few hun­dred thou­sand years, you’d need to pho­to­graph thou­sands of horse-feet and then ar­range them chrono­log­i­cally. Only then would you see a very slow and grad­ual change from soft toes to a sin­gle, hard­ened hoof.

It’s a bit like grow­ing up. You never re­ally think of your­self as be­ing big­ger than you were 20 years ago. But the pho­to­graphic ev­i­dence is clear. You used to be re­ally small. But the growth hap­pened so slowly, it only struck you ev­ery now and then how big you were get­ting.

Now, this isn’t the same mech­a­nism as evo­lu­tion, but it gives a sense of how grad­ual the process is.

From ancestor bird to chicken, a long un­bro­ken line of birds kept lay­ing eggs, each chick was slightly dif­fer­ent to its par­ents, and over mil­lions of years these dif­fer­ences built up to a point where the bird now looked like what we call a chicken.

This is true of how an­i­mals in­volve, but in the spe­cific case of the CHICKEN and the CHICKEN EGG, we didn’t need to get into evo­lu­tion. Be­cause it turns out the an­swer to this ques­tion is re­ally easy, and doesn’t re­quire any knowl­edge of evo­lu­tion­ary the­ory at all.

One day there was a bird that wasn’t a chicken, and it laid an egg, and that egg hatched into a chicken. How do we know? Be­cause we were there and, very prob­a­bly, we made it hap­pen.

Specif­i­cally, hu­mans in Asia no ear­lier

Think of the cra­zi­est rooster you ever fled from and mul­ti­ply by about ten

than 7000 years ago, bred a red jun­gle­fowl with a grey jun­gle­fowl to pro­duce the do­mes­tic bird we Aussies call a bloody id­iot chook.

That’s right. Chick­ens are jun­gle­fowl like dogs are wolves (see box). Why don’t more peo­ple an­swer the ques­tion this way? Be­cause they don't think in terms of species, maybe. If some­one is try­ing to use a par­tic­u­lar an­i­mal to chal­lenge evo­lu­tion, the first thing you should do is check what the an­i­mal has sup­pos­edly evolved from. The chicken is Gal­lus gal­lus do­mes­ti­cus, a sub­species of Gal­lus gal­lus, , the red jun­gle­fowl. Be­cause of the chicken’s yel­low skin gene, and a few other ge­netic mark­ers, there’s strong ev­i­dence that the red jun­gle­fowl was hy­bridised with the grey jun­gle­fowl (Gal­lus son­ner­atii).son­ner­atii). son­ner­atii)

Why did this hap­pen? Some stud­ies sug­gest Asian cul­tures first bred red jun­gle­fowl for cock-fight­ing, around 5000 BCE. Fur­ther ge­netic anal­y­sis of chick­ens, though, shows that do­mes­ti­ca­tion took place in sev­eral ar­eas and even as far west as In­dia.

The red jun­gle­fowl was a good can­di­date for do­mes­ti­ca­tion be­cause, among other things, it can mas­sively boost its rate of re­pro­duc­tion when it has ac­cess to plenty of food. All we have to do is feed ‘em up, and the jun­gle­fowl pro­duces lots of eggs. Yummy!

At some point, what prob­a­bly started by ac­ci­dent be­came very much de­lib­er­ate, and do­mes­ti­cated jun­gle­fowl – true chick­ens – were in­tro­duced to Europe around about 3000 BCE.

Those were pretty mad chick­ens though. Think of the most cra­zi­est, peck­happy rooster you ever fled from scream­ing as a child, and mul­ti­ply by about ten. Get­ting chicken eggs, even as a Ro­man, would have been a bit of a test of for­ti­tude. You'd need a stick.

Re­cent DNA anal­y­sis of chicken bones shows that in the Mid­dle Ages, chicken breed­ers fi­nally be­gan se­lect­ing for birds that were less ag­gres­sive and which be­gan lay­ing ear­lier.

This is an im­por­tant point ac­tu­ally. Even over the time we’ve had the chicken – only 7000 years, give or take – we’ve con­tin­ued to change it. Just look at all the amaz­ing breeds and va­ri­eties at the Royal Easter Show. Quite what the Ro­mans would have thought of our hy­potro­phied breast-mus­cled, rel­a­tively bland-tast­ing frankenchick­ens cre­ated as a re­sult of in­dus­trial farm­ing, I shud­der to think. So the next time some­one busts out this tired old cliché of a sci­en­tific “gotcha”, you can now re­spond as we all should have for years. The egg came be­fore the chicken, be­cause the first chicken (well, the first clutch re­ally) had a red jun­gle­fowl for a mother.

The large im­age is a chicken, and the smaller (right, in­set) a grey jun­gle­fowl. The fam­ily re­sem­blance is very clear.

Like dogs, chick­ens have the ge­netic abil­ity to be bred into hun­dreds of dif­fer­ent phe­no­types.

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