The question is answered for the Chicken. The egg came first. There is no circle. If you take the question literally. The first genetic chicken popped out of an egg.
It does not answer the greater philosophical question of how life began, or even what life is.
A non Disney source:
howstuffworks.com
Which came first, the chicken or the egg?
This question appears regularly in the question file, so let's take a shot at it.
In nature, living things evolve through changes in their DNA. In an animal like a chicken, DNA from a male sperm cell and a female ovum meet and combine to form a zygote -- the first cell of a new baby chicken. This first cell divides innumerable times to form all of the cells of the complete animal. In any animal, every cell contains exactly the same DNA, and that DNA comes from the zygote.
Chickens evolved from non-chickens through small changes caused by the mixing of male and female DNA or by mutations to the DNA that produced the zygote. These changes and mutations only have an effect at the point where a new zygote is created. That is, two non-chickens mated and the DNA in their new zygote contained the mutation(s) that produced the first true chicken. That one zygote cell divided to produce the first true chicken.
Prior to that first true chicken zygote, there were only non-chickens. The zygote cell is the only place where DNA mutations could produce a new animal, and the zygote cell is housed in the chicken's egg. So, the egg must have come first.
And from Wikipedia:
Science and Evolution
Species change over time in the process of evolution. Since DNA can only be modified before birth, a mutation must have taken place at conception or within an egg such that an animal similar to a chicken, but not a chicken laid the first chicken egg.[11][12]
However, a mutation in one individual is not normally considered a new species. A speciation event involves the separation of one population from its parent population, so that interbreeding ceases; this is the process whereby domesticated animals are genetically separated from their wild forebears. The whole separated group can then be recognized as a new species.
The modern chicken was believed to have descended from another closely related species of birds, the red junglefowl, but recently discovered genetic evidence suggests that the modern domestic chicken is a hybrid descendant of both the red junglefowl and the grey junglefowl.[13] Assuming the evidence bears out, a hybrid is a compelling scenario that the egg came before the chicken. |
