Stated Clearly: What came first, the chicken or the egg? Evolution chimes in!

The theory of evolution solved the chicken or egg conundrum a long time ago... well, it did as long as the egg doesn't have to have come from a chicken:

I got this cool graphic from my old neighbor's facebook
page. Thanks Josh! He got it from a guy named James
who got it from... who knows, maybe he made it?

Animals appear to have been producing eggish-like structures since at least the end of the Precambrian era where sea sponges got their start. Eggs similar to those found in modern chickens first evolved as one group of reptiliomorphs left the water, eventually giving rise to modern reptiles, birds, and mammals.

When we look at the history of life on Earth, we don't see clear signs of vertebrates on land until roughly 395 million years ago. At that time we start seeing track ways, possibly of fish beginning to come onto dry land for short periods of time.

Photo by Grzegorz Niedzwiedzki, shamelessly jacked from
National geographic's website without any sort of permission.
Long live the internet!

And at about 375 million years ago we actually find bones of walking amphibian-like fish.

By Eduard Solà, CC BY-SA 3.0, from wikipedia

Early walking vertebrates appear to have been fully dependent on water for laying their jelly-like eggs as amphibians and fish still do today. Some frogs can lay eggs on land in extremely humid environments but without intense moisture, amphibian eggs dry out and die. This, in part, is because amphibian eggs lack an outer shell and a few membranes around their embryos. Fish, salamanders, and frogs lack the amnion, for example, one of several sacks that surround all reptile, bird, and mammal embryos as they develop.

Some frogs lay on land but only in humid environments

As reptiliomorphs began evolving from their amphibian ancestors and moving further and further from bodies of water, selection pressure for egg survival in dryer environments appears to have increased, favoring any modification that happened to prevent eggs from drying out. The eggs of modern reptiles and birds with multiple internal sacks and a relatively tough, dry outer shell was the end result (though modern reptile and bird eggs do vary in shell hardness from species to species).

When chickens began evolving sometime after the extinction of their non-avian dinosaur cousins, they were already using shelled eggs. So what does all this mean? What actually did come first, the chicken or the egg? The egg of course, by many millions of years!

I must add however, that my answer is null if you add a rule to the question saying the egg only counts if it was laid by a chicken. With that rule in place, the chicken had to come fist, but that's a stupid rule.

So that's that!
Jon Perry

P.S.
Here's a bunch of videos of different species of fish coming out on land for a brief stroll. Those little buggers are still at it!

David Attenborough vs Crazy Land Shark!