From The Gene:
In a famous story, a medieval cosmologist is asked what holds the earth up.
“Turtles,” he says.
“And what holds up the turtles?” he is asked.
“And those turtles?”
“You don’t understand.” The cosmologist stamps his foot. “It’s turtles all the way.”
When a mother bird protects her chicks, she is being guided by proteins, proteins created from instructions contained in her DNA. Those proteins determine her behavior and emotion and appearance.
A bird is the physical result of genes creating specific proteins, which were flipped on by other genes influenced by other protein, which were flipped on by other genes influenced by other protein, all the way back to the very first embryological cell.
It’s genes, “all the way.”
To a geneticist, “nature” is the genetic code. “Nurture” is the explanation of why certain genes were activated by protein and why other genes were never activated.
But which turtle is the nature part and which is the nurture?