You Two Are Related? How Siblings Can Be So Different

As a mother, pediatrician, and sister, I recognize all too well how different siblings can be. One brother might be a bookworm, the other a jock. One sister an optimist, the other a cynic.

Like me, you probably wonder how people from the same genes and the same environment can end up being so different.


oranges and apples

In the 1980s, Robert Plomin, a psychologist specializing in twin studies and behavior genetics, discovered something interesting (as summarized by Alix Spiegel in the article Siblings Share Genes, But Rarely Personalities). In regards to physical characteristics and intelligence, siblings were fairly similar. But when it came to personality, they were more like strangers. In fact, their personalities were similar “only about twenty percent of the time.”

That finding prompted the scientific community to ask:

How can children raised in the same family have such different personalities?

According to Spiegel’s article, three theories surfaced:

1) Divergence:

Given human nature, children compete with each other for their parents’ attention. As a result, if one child excels in academics, another might choose sports, hoping to stand out to his or her parents.

2) Environment:

Though on the outside it appears children in the same family share the same environment, they really don’t. Because kids differ in age, they’ll experience family events differently, particularly difficult events like divorce or death. For example, a mother’s cancer diagnosis will have different effects on a five-year-old than a twelve-year-old, and as such, each child will have different needs. The parents will then treat each child differently based on these needs. This in turn molds different personalities.

3) Exaggeration:

Children in the same family are often compared to each other, and their differences, even if minor, might be exaggerated. For example, “Oh, she’s the talkative one.” Or, “he’s the trickster.” Before long a label is born, reinforcing the trait and perhaps even escalating it over time.

Surely other variables mold our personalities, including neurochemical factors, but I suspect these theories hold some truth.

Carrie and Jo with fruit

So what got me started down this road of contemplation? My sister, a talented singer and songwriter, has recently branched out with her new band, ADHD. As I looked through the group’s page on Reverbnation and watched and listened to my extroverted sister sing and dance with a beer bottle in her hand, I thought, “Holy cow, how can we be so different?”

And then I thought, “Holy cow, my sister is really talented!”

My favorite song she wrote is “Suffocate” (the first one listed under songs). When I heard it, I couldn’t stop singing it.

But of course, as an introvert, only in the privacy of my own home…

Carrie and Jo (2)

Are you and your siblings different?

Related Articles:

Commentary: Why are children in the same family so different? Non-shared environment three decades later

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Rubin4Carrie Rubin is the author of The Seneca Scourgea medical thriller. For full bio, click here.   


244 Responses to “You Two Are Related? How Siblings Can Be So Different”

  1. Gail Kaufman

    The point about age difference rings true. Not only do children experience family events differently depending on their age, but parenting can change through the years. My sister and I are nine years apart and our parents’ parenting style evolved over the course of a decade. Therefore, my sister and I grew up under somewhat different types of parenting. I think that may explain some of the differences between us.


    • Carrie Rubin

      Excellent point, and I agree. First-time parents are worried about getting everything right. After another child (or two, or three…) they realize that’s an unattainable goal, and they often relax their style a bit.


  2. philosophermouseofthehedge

    This is always a mystery. One grandmother used to say “God made kids in a family totally different so there was no way parents would get them mixed up”. As good a reason as any?
    He had an interesting article. Birth order, culture, and society’s expectations of/for that child (birth order, sex, and “cuteness factor” all in that one) also play a role?
    Personally that labeling and repeated use of certain phrases used to describe or talk about a child to the child and to others is pretty important 1-6 yrs. (Behavior conditioning?)
    You and your sister are both creative – just in different ways and on different types of stages. You both play with words, word meanings, rhythm, and ideas.
    How nice you guys have each other.


    • Carrie Rubin

      Yes, we don’t see each other often, but when we do we have a blast. Lots of laughing. Who doesn’t like that?

      Yes, birth order is another intriguing contributor to our personalities. I know I have the middle child thing down well. 🙂

      Liked by 1 person

  3. frederick anderson

    Sadly unsibled (yes, I know microsoft, I just invented it, okay?) I can’t comment first hand, but certainly my sons are about as different as they can be. My eldest is an accountant and about as anal as an accountant can be (which is saying quite lot, actually), the ‘middle son’ runs three pub-restaurants at last count (he’s a very extrovert self-believer and achiever which scares me, because he works too hard), and my youngest is a truck driver. I think my youngest is most like me; i.e. a bit of a drifter who enjoys sampling rather than the whole deal. Dunno, I often wonder about DNA – like who arranges the knots? I guess the most we can hope for is that no-one in the family ends up in jail…


    • Carrie Rubin

      Ha, yes, having no inmates in the family is a plus.

      Sounds like your kids fit the personality types of birth order quite well, with your oldest being very detailed and your youngest a bit of a drifter. But I think birth order only explains a portion. That ‘knotty’ DNA plays its role too. 🙂


  4. camelliajapan2014

    right, I have a sister who lives in Tokyo , we are totally opposite.
    According to a new reserch, most people are actually more similar to their father… but why we are so different?(´・ω・`)
    It’s still mysterious!


  5. jeanjames

    Well one thing is obvious and that’s the talent both you and your sister share, it’s just displayed in different windows. I’m from a big family, 5 brothers, 1 sister, I’m so different from my sister, and in some ways similar to my brothers…maybe it’s all in the genes. I have twin nieces and they are very different in their personalities, as are my 3 children. What a great topic to think about!!


    • Carrie Rubin

      Thank you! Wow, six kids in your family. I hope you had more than one bathroom! Then again, four sibs were boys, so maybe they didn’t take as long to get ready in there. 🙂


  6. Celine Jeanjean

    That’s so interesting. You’re so right though, when I look at my siblings, we’re all so different. A big difference for us was that one of my brothers has Down’s. I’ve read that the experience of older siblings (I’m the oldest, and my brother who has Down’s is right after me) is very different than that of younger siblings. I can totally see how that’s shaped some of the differences between me and my younger siblings.
    I listened to suffocate by the way – your sister has a gorgeous voice! She’s a really talented singer – you must be very proud. Although you sound very different, you’re both clearly very creative, so you at least have that in common 🙂


    • Carrie Rubin

      Thank you, and thank you for checking out my sister’s song. 🙂 I am proud of her, and even though we’re very different, we have a lot of fun together when I go to New Hampshire to see her. Even though she can never drag my introverted self out to parties…


  7. roughwighting

    Great points in your post. My brother and I are NOT two peas in a pod. Only 18 months apart, if you met us you would never ever guess we’re from the same family. But, the good news is that we like each other and get along really well. I’m having a great time watching my daughter’s three little ones grow into personalities. As far as I can tell so far, none of them is alike.
    I love how you appreciate your sister’s differences, and her talent. Sweet!


    • Carrie Rubin

      I think you touch on a key point–just because siblings are so different, doesn’t mean they can’t get along. In fact, I think it’s those differences that make it so fun. They certainly make family gatherings more interesting!


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