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Asked by briancassidy to Cathal, Ciara, Emma, Michael, Sive on 14 Nov 2013.
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Emma Cahill answered on 14 Nov 2013:
Hey Brian,
Im not going to pretend to know the answer for this for sure but I have a feeling it may have been the egg… and I’d like to hear what the scientists have to say for this question!
I always think this is a question about evolution kind of.
What we would need to know is whether the non-lethal genetic alteration or mutation that generated the new species is more likely to occur in adult animals or in embryos in the egg right? Are adult animals more exposed to mutation-inducing environment than eggs?? 😯
I need coffee after that one Brian! thanks for starting it!
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Sive Finlay answered on 14 Nov 2013:
Hi Brian,
Great question! There are arguments for both sides but I like the one put forward in this video http://www.mnn.com/earth-matters/animals/stories/finally-answered-which-came-first-the-chicken-or-the-egg which says that the egg came first.
The main point they’re trying to get across in the video is that there was no single switch which produced the first chicken. Evolution happens through gradual mutations and the formation of new species usually takes place over many generations. So there wasn’t some bird ancestor which laid an egg which produced a fully-formed chicken. Instead the mutations and genetic changes which eventually produced chickens as separate species happened very gradually. At some stage two chicken-like ancestors produced an egg which had genetic changes that eventually formed the basis of a new species of chicken.
I think Emma’s right that adults are more likely to be exposed to environments that produce mutations. Our cells and constantly dividing so there’s a good chance that something will go wrong at some stage and produce a mutation. But, if we’re going with the idea that two “proto-chickens” mated to produce an egg which had genetic alterations that eventually led to the evolution of the first chicken then we can’t just rely on the knowledge that adults are probably more exposed to mutation-producing environments. For mutations or genetic alterations in adults to affect the evolution of new species they have to occur in germ line cells (sperm or unfertilised egg). Otherwise the genetic alterations won’t be passed onto the next generation. I guess the other alternative is that some sort of mutation occurs in the egg (at the single-cell stage, not the one you use for pancakes) after it has been fertilised so the genetic change arises in the egg itself and is not directly passed down from the parents but I don’t know if this can happen and, if it did, surely you could still trace the source of the genetic change back to the parents because ultimately that’s how the egg was formed?
Okay so I’m getting all muddled up in circles now – think I’ll join Emma for that coffee!
Sive -
Michael Nolan answered on 15 Nov 2013:
Hey Brian,
I think this is one of those misunderstood types of questions and I would say neither. It always gives the impression that an egg was (somehow) produced and from that came the hen or that there was a *first hen* that was the first to lay an egg. I think we need to teach evolution in our schools and soon!
Egg laying is a dominant way to produce offspring, so there is nothing special about the hen/egg scenario; you could ask about the frog and frogspawn for example.
The hen, as we know it today, evolved over a verrry long time from some ancestor with tiny changes that accumulated so much so that compared to the animal moving down a different evolutionary path, it became so different that it was its own species.
But that ancestor would have likely laid eggs and the modern hen kept that process of gestation.But what I dont know is the evolutionary path that lead to delivering offspring from an egg, that would be a good question.
so perhaps an answer is that “some distant evolutionary ancestor of the hen” came first 🙂 that is a mouthful!
M
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