An unfertilized chicken egg is obviously alive while it is still in the chicken’s reproductive apparatus. The yolk of the egg is the ovum of the chicken, and it metabolizes nutrients, maintains membrane potentials, etc. If it was not living tissue it could not be fertilized. After fertilization, ongoing cell division forms the germinal disk on the yolk, etc., and eventually you get a chick.
At some point the egg is laid, whether fertilized or not. Are the unfertilized eggs still alive at the point that they are laid? By ‘alive’ I mean only is the ovum still metabolically active - consuming stored nutrients, making ATP, transporting ions across membranes, maintaining homeostasis, that sort of thing?
I know that all eggs in the grocery store have been refrigerated at some point, which probably irreversibly interrupted these processes (i.e. killed the egg) if they hadn’t already stopped, but what if the egg was not refrigerated?
I don’t have any moral or esthetic qualms about the issue; I’m just wondering at what point the ovum of the egg goes from living to nonliving: before the egg is laid? When (if) it is refrigerated? After n weeks of sitting on the counter? When I cook it? For this discussion, let’s try to keep the philosophizing about ‘what is alive’ to a minimum.
I can’t claim to be an expert on avian physiology but have owned chickens from time to time.
The yolk of an egg is not the ovum but rather, lunch mom thoughtfully packed along before sealing the package. The ovum inside the egg consists of exactly one cell, haploid if it’s not been fertilized, diploid if it has. In either case it’s too small to be noticed. There might be some ancillary cells (see the first sentence) but they are not noticeable either.
When we were keeping chickens in a rural area, we let them run loose so they would lay eggs in a variety of places. We’d check the usual locations when collecting but every so often would find one some place unique. Not knowing how long it had been there, rather than risk eating it we’d recycle it (chickens will eat anything that holds still long enough) by carrying it to the henhouse and smashing it . We didn’t want the hens pecking one open and discovering the golden treasure inside. If the egg was truly old, there might be a white speck in the surface of the yolk but that’s about it. A friend of mine who was tagging along during this process was keenly disappointed there wasn’t a real chick embryo inside.
In any event, it would be hard to say where along the whole thing the ova ceases metabolic function. For that we’d need a real bird expert.
The yolk is a high-energy-density collection of nutrient material, but it is a part of the ovum. The nucleus and remaining cytoplasm of the ovum is dwarfed by the volume of the yolk, but the yolk lies inside the membrane of the ovum. I believe that after fertilization it is cleaved off and the subsequent chicken embryo cells lie on top of the separate yolk.
My intuition agrees with those above; there will be metabolic activity for a while, which will gradually run down. There will be some point at which the egg will irreversibly die (even if you could implant an intact and functioning nucleus, which could go on to embryo in a fresher egg). Even after this point, the moribund egg will continue to metabolize for a bit, kind of like a ghost town may keep a few inhabitants for a while after the silver mine has “played out”.
Naïve question - at what point in it’s development is a bird egg subject to fertilization?
There is a parallel situation with fish eggs. Once they are released from the female, fertilized eggs develop. Unfertilized eggs are almost immediately attacked by fungus.
It would seem there is a point in bird development beyond which fertilization cannot occur. Beyond that point there is random cell activity that has no evolutionary value.
An extension of the question is - when does a human die. Hearts are removed from humans and flown around the country while the donor is being cremated. Is the donor alive because there is cell active in some part of his body?
The evolutionary value is secondary for this consideration, I think.
A sterile person with no known or living relatives (say a person adopted from overseas, now sterile and childless) has “no evolutionary value”, but is still considered “alive”.
The last question about heart transplants seems to go against OP desires to not wax too philosophical in this thread.
It is worthwhile to note that we do know of cells which are still “alive” in the sense that they are undergoing metabolic processes, but are “destined to die” (in some greater sense than we are all destined to someday die).
For example, cells undergoing aptosis are at some point absolutely going to die, even if they’re not quite dead yet. It is believed that shortly after a stroke, there will be within the ischemic territory some dead cells, some live cells, and some cells that are “alive” but moribund, just too far gone to recover and slated to die. After radiation therapy, there can be some cells that are too damaged to reproduce, but are okay to chug along, maybe dying when they try to divide.
I think an unfertilized egg is somewhat like these examples. Like a town after the last mill closes, or a person with devastating injuries, or a landing party member in a red shirt, just slated to die, but maybe hard to tell exactly when.
IANACF, but it may be because if they figure out they can find food by pecking an egg open, no egg would survive intact long enough to be collected by the chicken farmer.