As per subject: why do chickens continuously lay eggs even if they are not fertilized?

Is this sort of behaviour found in other species of birds (or other egg-laying animals), or only in chickens? Is it natural, or domestic chickens have been specifically bred for it?

If it's natural, what kind of sense does it make to divert energies and nutrients to continuous lay unfertilized eggs which have no purpose other than being possibly eaten by someone else? How could such a wasteful reproductive behaviour have evolved? Even if it has been specifically selected for in breeding, it still seems to make very little sense in the first place.

  • $\begingroup$ I do think much of it is selection, like milk production in Holsteins. Some ducks are also great "layers" (the industry term for fowl that lay a lot of eggs for extended periods.) Not like chickens, but yes. Also guinea hens, quail, and probably a few other birds (but I can only speak to the birds I've raised.) $\endgroup$ Mar 16, 2016 at 2:46

1 Answer 1


Chickens are domesticated Red Jungle Fowl. In the wild, Red Jungle Fowl live in flocks with one rooster for every few hens (where "few" is probably less than five in the wild, though in zoos flocks may be larger and have a higher rooster:hen ratio). Since one rooster can fertilize many hens, in the wild virtually all eggs will be fertilized. Since jungle fowl, of course, lay far fewer eggs than domestic chickens, the cost of the extremely rare unfertilized egg will be low.

In principle, there could be a molecular mechanism that checked for evidence of fertilization before allowing an egg to be laid, but of course such a mechanism would have its own costs, and would almost never actually be useful.

  • $\begingroup$ I find the "in the wild virtually all eggs will be fertilized" argument a good explanation to not even bother checking before laying an egg; however, I don't really understand the "jungle fowl, of course, lay far fewer eggs than domestic chickens" part. Why is this the case? $\endgroup$
    – Massimo
    Mar 15, 2016 at 18:19
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    $\begingroup$ At the moment you have no evidence to support your answer and in my opinion make little attempt to answer the question beyond some opinion $\endgroup$
    – rg255
    Mar 15, 2016 at 18:48
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    $\begingroup$ Jungle fowl lay fewer eggs than chickens because chickens have been selectively bred for 5000 years to lay many eggs. $\endgroup$
    – iayork
    Mar 15, 2016 at 19:17

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