A chicken is defined as a fully matured bird of the subspecies gallus
gallus domesticus.
A chicken egg is defined as an egg which will eventually hatch and
will result in a bird that will grow up to be a chicken as defined
above.
It then follows that the last pre-chicken bird or proto-chicken on one
sunny day laid an egg with a mutation that caused this egg to produce
a chicken rather than a proto-chicken.
Hence, the egg came first.
So there's that.
But wait, that's just one egg! Where do all the other chickens come
from?
