Most biologists will answer confidently when asked 'which came first, the chicken or the egg?' but the answer may depend on what type of egg you're talking about.
You've heard the age-old riddle:"" Taken metaphorically, it's a meditation on the futility of determining the cause of a self-perpetuating cycle. Taken literally, it's a great question for evolutionary biologists.Most biologists state unequivocally that the egg came first. At their most basic level, eggs are just female sex cells. Hard external eggs that can be laid on land were a game changer for vertebrates.
There were plenty of land-based vertebrates laying amniotic eggs in the Carboniferous, Permian and Triassic periods, but the most famous of these animals are the dinosaurs. Stein has studied some of the earliest known dinosaur eggshells, which come from the early Jurassic period, about 200 million years ago. These eggs had extremely thin outer shells, only about 100 microns thick."That's the thickness of a human hair," Stein said.
So the egg definitely predated the chicken. Case closed, right? Well, not quite. If we're talking about the first chicken egg, the story changes. At some point during the domestication process, the last ancestor of modern chickens would have laid an egg containing an embryo with enough genetic differences to make it distinct from its parent species. This embryonic chicken would have developed in the not-quite-chicken egg before hatching. Then, after reaching adulthood, it would go on to lay the first proper chicken egg. In this way, the chicken could be said to predate the chicken egg.
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