Adeline excitedly walks down the steps, holding onto the railing. As soon as her feet hit solid ground she takes off, racing to the playground, followed by her four school-mates. Within moments, Adeline, Quinn and Logan are up on the swaying bridge, jumping up and down and screaming together. Adeline runs for the slide and Quinn and Logan follow her. They all slide down and pile up at the bottom, laughing and shouting the whole time. They run around the play equipment to the stairs and soon they’re back up on the bridge. Adeline starts shouting “Ba ba ba!!!” and Quinn and Logan join in.

Meanwhile, Quinn’s twin sister, Grace, came down the steps with the rest of them but has since been wandering around the edges of the playground, looking at flowers and talking quietly to herself. When she comes near me, where I sit on the bench taking it all in, she gives me a happy little smile. She’s not lonely – she’s perfectly content playing by herself. Parker, the final child in Adeline’s class, is also playing by himself. He sits in the little car and pushes himself around. Every few minutes he goes over to where Adeline, Quinn and Logan are playing and he tries to get involved. But he inevitably goes off on his own again. He wants to play with them, but he’s shy.

This is the dynamic that plays out every day when I go to pick Adeline up from school. It’s so invariable that it’s striking. These children, ranging in age from 17 months (my sweet Adeline is the youngest) to 2.5 years, have amazing, distinct and realized personalities. Some are outgoing, loud, active, extroverted, while others are quiet, shy, calm, introverted. I watch them all and the truth seems undeniable: this is genetic.

I’ve talked before about how “nurture” can play a big role, and I certainly still believe that. At several years old, these children have all had plenty of nurturing, and different parenting could have played a role in their different personalities. But then I think of Adeline. From the moment she was born, she was a mover. She could hold her head up the day she was born. Seriously. People were shocked. She rolled over at two months, started scooting herself backwards around the room at three months, starting army crawling at five months, regular crawling at six months and walking at nine months. She was never going to be the one quietly walking around the edge of the playground. Not my Adeline.

And then consider the (non-identical) twins, Quinn and Grace. Presumably they’ve had a pretty similar upbringing (I’ve never met their parents), but they couldn’t be more different. Adeline’s teacher once commented that Adeline seemed more like Quinn’s sister than Grace. Even though Quinn is a year older than Adeline, he loves to play with her. It’s adorable.

Finally, I look at little Logan. Adeline’s teacher told me that the first year of his life was somewhat unstable and that, as a result, when he first came to school he was very insecure. He still asks me every day, “Is my mommy coming?” (I pick up Adeline earlier than the other kids get picked up.) But even that insecurity couldn’t crush the little personality that was inside him. He’s an active, happy boy and he loves to play with other kids. He’s always running around with Adeline and Quinn, even if he does sometimes pause to ask me when his mommy is coming.

Which all leads me to wonder: how much do we really affect our children? How much do our parenting choices matter in the grand scheme of things? Our genes, of course, determine where we start, but where do we go from there? We know that environmental factors can turn genes on and off and that epigenetics plays a large role in how a genotype actually plays out in a given human being. But how does it all fit together? Of course, no one knows for sure. But it’s certainly food for thought.