Complex sentence: The first documented example of epigenetics affecting behavior was provided by Meaney and Szyf while working at the McGill University in Montréal in 2004 who discovered that the type of mothering a rat receives in infancy determines how that rat responds to stress later in life.
Split into simpler sentences: The first documented example of epigenetics affecting behavior was provided by Meaney and Szyf. While working at McGill University in Montréal in 2004, they discovered that the type of mothering a rat receives in infancy determines how that rat responds to stress later in life.