Found very interesting post by John Vespasian - Why every chicken must break out of its own shell:
“Egg-shells look deceivingly fragile. The truth is that breaking out presents almost insurmountable problems for chicken. Baby chicken don’t even know that they are inside a shell, since their eyes are still closed.
What makes the situation of infant birds even more critical, if that they have very limited time to accomplish their feat. The little oxygen that gets through the shell won’t keep them alive for long. At a certain moment, almost by magic, baby chicken begin to move and break out of the egg.”
Read the rest here.
Further reading: