Authors Lisette Schuitemaker and Wies Enthoven have spent years researching the inner-workings of first-born daughters.

We had the chance to catch up with Lisette and Wies to find out more about The Eldest Daughter Effect and how first-born daughters grow up to become “big sisters”… and so much more.

Based on your book, it seems as though many, if not most, first-born daughters grow into responsible, dutiful, thoughtful, expeditious, and caring big sisters. What factors lead to the development of these characteristics in eldest daughters?

Just imagine for a moment the only child. Her mother dotes on her. Her father, she wraps around her little finger. She is the sun all planets, grandparents included, revolve around. All is well in her world.

Then danger looms on the horizon when her mother cannot lift her anymore and her father talks about a new baby soon to make a debut.

They make it sound like a joyous and exciting time so their first-born daughter is soothed. But once baby number two is on the scene, her world is changed beyond recognition.

No longer is she the center of the universe as now another child is cradled on her mother’s lap. A baby that needs so much time and attention that she, the eldest daughter, needs to re-evaluate her position within the family constellation.

One eldest daughter we spoke with said her mother often told her the story of how she had set her younger sister in a wastepaper basket after a few weeks. ‘So! Now it can be all about me again,’ is how her mother had interpreted her act.

Psychologists confirm that, however close siblings may become, the reconfiguration of the family comes as a shock to the first child, as shown by many unexpected changes in the older child’s behavior.

So, what are a few of these behavioral changes?

Speaking generally, many girls tend to adapt. They figure out how they should act so they stand the best chance of still being loved and appreciated. They become the good girl. Eager to help their parents, they develop an eye for what needs to happen and then they make sure they can do it.

They take responsibility, first for themselves—’Don’t worry, mama, I can dress myself,’ and then for their siblings— ‘Don’t worry, mama, I will look out for them.’

Taking responsibility, being diligent and dutiful, thus becomes second nature.

Caring for others makes these girls into practical, hands-on individuals. They may not be the life and soul of the party, but they grow up to be thoughtful women who take themselves, others, and life seriously.

They are the ones, like Hillary Clinton, Angela Merkel, Nicola Sturgeon, and Christine Lagarde, who take responsibility.

They are the ones who, like Beyonce, Arianna Huffington, and Oprah Winfrey, have a message to tell the world and are able to build the platform to deliver it.

The day a single child becomes an eldest daughter is a defining moment that sets girls on the course to become the responsible, dutiful, hands-on, thoughtful, and caring women everyone counts on.

This article was co-written by Wies Enthoven and Lisette Schuitemaker.