The nature versus nurture debate is one which families who've adopted are no doubt familiar with.
For one mum, it's a debate which now comes with painful implications, as she admits she loves her biological daughter more than her adopted daughter.
Having known since the start of her relationship with her husband that they'd have a family via adoption, the unnamed woman from the US then unexpectedly fell pregnant.
"A year into our marriage I got pregnant with our daughter June," she reveals on Reddit.
"It was unplanned, but we were financially stable and wanted children anyway, so we were both excited to become parents.
"When June was 2, we adopted a baby girl, Charlie.
"We were involved during the pregnancy and there for her birth."
Despite this, the mum admits there was still a feeling of being slightly disconnected from Charlie.
She continues: "From the beginning, I felt a difference between my love for my daughters. When I held Charlie, I adored her, but it felt more like holding a friend's kid than my own."
Following a heart-to-heart with her husband, it turned out he felt the same.
"He said that he felt the same awkwardness, but he was sure it would pass as we spent more time with her. I agreed."
The mum goes on to say all the advice she has come across states this is normal, and that time spent bonding would "fix it".
While this is true of her husband's relationship with Charlie, she reveals, "Three years later, my feelings have not changed.”
In many instances, behavioural issues inhibit bonding, but this is not the case.
"She is a wonderful little girl, who is, in many ways, better behaved than her sister who is two years older.
"Don't get me wrong, I absolutely love my adopted daughter.
"But not in the same way I love my biological daughter. I can't get over the feeling that she's not my kid or that I'm taking care of my friend or family members child and not my own."
While most people agreed the mum wasn't a bad person as she feared, they did warn that her daughters may have already picked up on how she feels.
In particular, people who themselves were adopted warned her of this.
"(I'm) adopted here too - I always knew my father felt differently towards me than my sister (who is their bio-kid) though he would never admit it," one woman replied.
"Kids always know... we may not let on that we do, but we do."
One man agreed: "I am adopted, the only one of seven children in the family, and definitely felt a bit different than my bio siblings."
However others were harsher in their judgement of her.
A mum responded with: "This is not normal and it's not okay." a mum said.
"It doesn't make you a bad person generally but something in you is broken."
"I hope that little girl never learns the truth about how you feel about her," another mum added.
"Normal adoptive parents love their adopted children just as much as biological parents do," another said.