Once upon a time, there was a seed. The seed would grow if given good soil, water, and sunlight, and weeds were pulled.
People didn’t like pulling weeds, so they developed sprays to kill weeds – except it would kill the plants too.
So, scientists developed a new seed that would grow a plant that would not die when sprayed with the weed killer.
Then people, and chickens and cows ate the food from the plants that would not die when sprayed with weed killer.