Short answers, pulled from the story.
The word sister emerges from the Proto-Germanic root swestēr and the Old Norse swestr to describe a female sibling. This linguistic thread stretches back thousands of years to define the bond older than language itself.
Research published in Child Development in 2002 by Volling, McElwain, and Miller highlights that sisters are more likely to exhibit jealousy toward their siblings than boys are toward their brothers. This jealousy is a complex interplay of emotion regulation and family characteristics that influences how sisters interact with the world and each other throughout their lives.
A study conducted in Perth, Australia revealed that girls having only younger brothers lose their virginity on average more than a year later than the average. This delay is hypothesized to be attributed to the pheromones in their brothers' sweat and household-related errands that create a unique biological environment.
Boys with older sisters were less likely to be delinquent or have emotional and behavioral disorders, suggesting that the presence of a sister can have a stabilizing effect on a boy's development. Younger siblings display more needy behavior when near their older sister, yet they are also more likely to be tolerant of an older sister's bad behavior.
Men without sisters are more likely to be ineffectual at courtship and romantic relationships, a finding that underscores the critical role that sisters play in the social development of men. The influence of a sister on a man's ability to navigate romantic relationships is profound, shaping his understanding of women and his own role in a partnership.