What is first egg or hen?

This question is an age-old paradox known as the "chicken and egg" dilemma. Logically, both cannot have come first.

Biologically, eggs came first. There is evidence that suggests that early reptile species (proto-birds) produced amniotic eggs that were not hard-shelled (like reptile eggs we see today). Over time, these proto-birds evolved and adapted to produce hard-shelled eggs similar to chicken eggs. As these reptile species diverged and developed into early bird species, laying hard-shelled eggs became a characteristic of all bird species.