I am watching this year's clutch of Decorah Eagles hatch. (Two down, one to go.) In particular, watching the mama eagle do her thing with the eggs, and knowing a bit about what is to come, I thought about the chicken and egg thing.
And what I thought is that the mama eagle (or chicken) doesn't just have to produce an egg and that's the end of it. It would seem she has to know about keeping the eggs warm and moving them around before they hatch and then she has to know how to feed the eaglets until they become mature enough to feed themselves; and she has to have a willing partner to bring her the food to prepare for the eaglets.
We're suppose to think that all of this just evolved to the way it is now, slowly over eons as starving eaglets waited for the right cosmic ray to come along.
ML/NJ
Yep. We think that because there is plenty of evidence from both the fossil record and from living examples of creatures who are somewhere in between complete caring for their young and complete disinterest beyond laying the eggs. Frogs happen to exist all along that spectrum, as do sharks and many other species.