Are the eggs we eat the result of 'chicken periods'?
Are the eggs we eat the result of 'chicken periods'?
I’ve heard this analogy many times and thought that it might be useful to write about it so that we can better understand why chickens laying eggs is not the result of them menstruating.
A common misconception
Comparing a chicken laying eggs to human menstruation is a common misconception..
It is biologically inaccurate. Here’s why…
Differences in Reproductive Systems
Human menstruation is a process unique to certain mammals, which involves the monthly buildup and shedding of the endometrium in preparation for potential pregnancy. If fertilisation and implantation don't occur, hormones trigger the breakdown and expulsion of this blood-rich tissue as menstrual flow. The ovum itself is tiny and microscopic—it's not part of the menstrual discharge.
Chicken egg-laying is ovulation, as opposed to, menstruation. Chickens lack a uterus or endometrial lining. They have an oviduct, which is where a mature ovum (yolk) is released from the ovary. It gets enveloped in albumen (egg white), membranes, and a shell, and is laid (whether it’s fertilised or not), roughly once a day in laying hens that aren’t in a commercial setting. Egg laying is driven by light cycles and hormones, without any "shedding" of tissue.
No "Failure or Shedding in Chickens
Menstruation occurs as a response to no pregnancy. The body discards unused uterine tissue to reset the cycle.
However, Hens lay eggs proactively as part of their normal reproductive cycle, regardless of fertilisation. Unfertilised eggs aren't "waste." They are undeveloped ova. There's no hormonal trigger for breakdown or expulsion of built-up tissue, as birds don't invest in an internal pregnancy environment like mammals do.
Evolutionary and Anatomical Context
Mammals like humans evolved internal gestation, leading to complex cycles with menstruation in some species to efficiently manage reproductive energy.
Birds evolved external development (eggs laid and incubated outside), so their system prioritises producing robust, self-contained eggs. This makes egg-laying efficient for species survival but unrelated to menstrual shedding.
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