Why did the chicken cross the road? Science will never know.
How do chicken eggs get fertilized? Science knows this: sex. I've seen it happen with my own eyes...
My brother-in-law is an organic farmer and he has a growing herd of chickens. I'm not sure if herd is the appropriate term, but you get the idea: a large group of chickens. Over lunch at work we were talking about cage free eggs. The yolk is a more vibrant yellow and they just seem to taste better. Then a debate erupted about eggs, and if they were always fertilized or not. The one fact I was sure of was that chickens lay eggs with or without the presence of roosters. In fact, any roosters in my brother-in-law's herd are there by mistake. He hatches his chicks from eggs which are supposed to be rooster free. Yet there is always an odd rooster, so now he has about 3. Roosters are more aggressive than chickens and they don't lay eggs, so there isn't much need for them on the farm unless you have some sort of nostalgia for that cock-a-doodle-do thing they do.
There were many theories here at work... that all eggs chickens lay are fertilized, that the rooster goes by and sprays the already laid eggs (kind of like fish? Sadly this theory was laughed off the table, I kind of like the visual), and lastly that the rooster and the chicken somehow go about the act of love-making. Nobody was certain, and nobody wanted to search for the answer on their phones. It looked like they were depending on me to go right to the very source. I promised to bring definitive information back to work after my next visit to the farm.
It was a drizzly May day around 6:30 a.m. I had just spent a few moments with my wife and 2 month old, trading smiles in what is definitely the best part of waking up. I went out to help my brother-in-law with farm work for the day, and was instructed on how to release the chickens from the coop, feed them water and cornmeal, collect eggs and add some fresh hay. Pretty exciting stuff when most mornings are spent checking email and opening up files to line up a day's digital work. OK, most people probably prefer reality B, but for whatever reason... my soul beckons me to the place that smells like chicken shit.
As I approached the coop it shook with a frenzy of animal energy, the chickens definitely smelled their freedom approaching. I flipped the latch as a blur of chickens and feathers burst forth to the piles of food I had dumped nearby. The herd made it's way to the food and set to work, except for an unlucky chicken that was promptly mounted from behind by the more dominant rooster. I watched out of the side of my vision as I went around the back of the coop to collect eggs. The act was quick and seemed very far from any sort of love. There in that cold morning air, the eggs brought warmth to my hands as I gathered them up. Some of them were likely fertilized, but I was cutting any chances of life short. These eggs were for market.
That's the science of it all, rooster mounts chicken, egg gets fertilized. The chickens don't know the difference, but that egg has the potential to hatch a whole new life form. The only difference you might see when cracking open an egg is a small blotch of red in the yolk.