Ingon ani na ay:
Chronologically, ang itlog ang nag-una. Sa evolution, ang manok ug ang tanang mga langgam, gikan sa dinosaurs. Meaning, wa pay manok, diha na ang itlog or the ability to lay eggs kay mangitlog man tong mga dinosaurs.
The dinosaurs continued to evolve until they became birds and, in our discussion's case, some became domesticated birds or chickens. What remains in spite of the millions of years of evolution is their egg-laying capability which is for them a perfect way of producing off-springs.
So there. Nag-una ang itlog sa chronology although ang sulod adtong itloga di pa manok kun dili ang ancestors sa mga manok. However, even the ability to lay eggs in order to bring forth off-springs is a product of evolution. By natural selection, animals, even plants, survive if they can find the most suitable conditions and capabilities for their species. So, there has to be a species first that has to re-engineer it's body and habits in order to ensure survival. Bearing that in mind, it is the dinosaur, the great-great-great grandmother of chickens, that engineered its body in order to succeed in life. I don't think that an egg can do so much to re-engineer itself for it to survive.
See? It's not as simple as chicken. You have to view it in the perspective of evolution.