Eggs, as reproductive structures, existed long before the emergence of modern birds, including the so-called domestic chicken.
Dinosaur egg fossils show that egg-laying preceded the emergence of chickens, tens of millions of years ago!
The hen, the result of a genetic mutation in an egg!
A recent study explains that the first true chicken was born from an egg laid by a close ancestor, the proto-chicken!
It was in this egg that a crucial genetic mutation occurred, giving rise to the chicken as we know it today!
This means that it was indeed the egg containing this mutation that appeared before the animal itself!
