For all that the cultural mythology insists that mothers love all their children equally, the truth is that mothers (and fathers, for that matter) treat their children differently. In fact, its so much a part of family dynamics that its got its own acronym: PDT (Parental Differential Treatment). Some differential treatment is inevitable, having to do with the ages of the children; a four-year-old may feel that her infant sister is getting all the attention, for example, and unless the mother actively works to try out to balance out the scale by making sure that her older child has time alone with her, its probably going to be true.

A mother may favor one child over another because of whats called goodness of fita match of personalities between the mother and one child, and not another. Just imagine an introverted mother who needs quiet with one child whos just like her and then imagine her with a rambunctious, high-energy kid who needs attention 24/7. Go ahead: Ask yourself which child shes going to be most comfortable with.

The gender of the child tooagain, this is never openly acknowledged by mothers or anyone other than researchersmay also play a role. Women who had mothers who were jealous or competitive or who are uncomfortable around other women may feel safer and more competent around a male child.

These are relatively benign examples of favoritism but just because they sound benign doesnt mean that they dont have profound effects on the child whos not the favorite. Study after study shows that they doand the more pronounced the differential treatment, the greater the damage done.

For example, Judy Dunn and Robert Plomin demonstrated that observing differential treatment of a sister or brother had a greater effect on a child than the actual love received from a parent. (Again, this once again proves the psychological truism that Bad is Stronger than Good or that negative experiences affect us more than positive ones.) Other studies show that children who are given more support and affection by their mothershaving the favored statushave greater self-esteem and better adjustment skills than their discounted siblings who are likely to be at a greater risk for depression. A study of young adult children confirmed these findings, along with diminished sibling relationships when PDT was part of the family dynamics. Needless to say, the effect of differential treatment was greater when the favored sibling was the same gender.

Sometimes, a mothers favoritism dominates how everyone in the family relates and connects. A daughter may become scapegoated or she may simply fade into the woodwork. Here are some effects on her personality and development, as reported by daughters themselves.

1. Constantly striving to be seen and appreciated

Some daughters will end up on a treadmill just trying to get their mothers attention; that was the case for Lydia, now 57: I was the one in the middle, and both my older sister and my younger brother were needy in ways that made my mother feel competent and good about herself. I was independent and thus didnt need anything special so I got no attention at all. There were celebrations for my siblings achievements but not mine. To this day, all these years later, I still feel invisible in my own life some of the time. Many of these daughters will become people-pleasers, inadvertently recreating their childhood patterns in their adult lives unless they recognize them first and can begin to recover and change.

2. Feeling left out and inadequate

The hit to a daughters self-esteem can be enormous if theres a siblingespecially a sisterwho can do no wrong and who happens to be talented and high-achieving. That was the case for Emily, 46, now a manager at a small company and divorced: My sister is two years younger than I, and my complete opposite. Im a brunette; shes a blonde. Im quiet and shes outgoing. You get the picture. I did well in school but not as well as Leslie who was a star at everything she did and our mother was her biggest fan. Ive been dogged by not feeling good enough all of my life. I married someone who made me feel as unspecial as my mother did and this last year, I finally got the courage to leave him. Still, it feels like I have a long road ahead.

3. Not seeing herself clearly

As Ive written before, a mothers face is the first mirror in which a daughter catches a glimpse of herself and if her mother ignores, marginalizes, or criticizes her relative to another child in the household, her ability to see her own gifts and abilities can be vastly impaired. Rose, 36, was one of three children, and the only girl: My mother acted as though she didnt have a daughter most of the time, unless she needed me to do something like laundry or walk the dog. I did well in school, unlike my brothers, and so my mother downplayed my achievements, saying that being good at school didnt make me smart. And, for the most part, I believed her, even after I won awards and ultimately a college scholarship. I still have trouble shutting the voice in my head offthe one that says that everything I do right doesnt really matter. Im an attorney and both of my brothers are construction workers, but that hasnt changed how my mother treats me Im still the odd girl out. Variations on this themesome more drastic than othersanimate many daughters stories, especially if they are the only girls.

4. Always feeling like she doesnt belong

This is the single most damaging legacy of an unloving mother but its made much worse when there isas there often isdifferential treatment of the other children in the household. Its not just being excluded that damages the daughter but, often, the belief that somehow the exclusion or singling out is actually justified. The world in which a child grows up is small and constricted, and the mother controls how what goes on in that world is to be interpreted after all.

Being the odd girl out in her family of origin shapes a daughters sense of herself and how she connects and relates to others. Its only by seeing that she did nothingyes, nothingto warrant that exclusion that she can begin to find the pathway to becoming whole.

Photograph by Molly Porter. Copyright free.

Dunn, Judy and Robert Plomin. Separate Lives: Why Children Are So Different. New York: Basic Books, 1990.

Jensen, Alexander C., Shawn D. Whiteman, et al. Life Still Isnt Fair: Parental Differential Treatment of Young Adults, Journal of Marriage and Family (2013), 75, 2, 438-452.