"Nature" means the influence of an individual's genetic make-up on their development and learning. "Nurture" means the impact of the individual's family, education and upbringing.
There have been many studies of the impact of these two factors. The most interesting of these involve twins separated at birth. Here is the introduction to an NPR story about one such pair:
What is it that makes us who we really are: our life experiences or our DNA? Paula Bernstein and Elyse Schein were both born in New York City. Both women were adopted as infants and raised by loving families. They met for the first time when they were 35 years old and found they were "identical strangers."
Unknowingly, Bernstein and Schein had been part of a secret research project in the 1960s and '70s that separated identical twins as infants and followed their development in a one-of-a-kind experiment to assess the influence of nature vs. nurture in child development.
Now, the twins, authors of a new memoir called Identical Strangers, are trying to uncover the truth about the study.