The first time I heard the twins’ heartbeats, they were quite different. One was more rapid than the other, and my doctor laughed heartily. “They’ll have totally different personalities,” she explained to me.

It turns out that it wasn’t a joke: they had different personalities right out of the womb. My husband describes looking down at our hour-old newborns and thinking how one seemed alert, curious, and full of beans, while the other seemed helpless, her little hat slipped in front of her eyes, quietly pouting. From the outset, one twin has seemed like a tiny adult, raring to go and get into trouble, anxious to crawl away, while the other happy to be a roly-poly baby, able to explore simple toys for ages.

These personalities are still who they are today. Olimpia, our big trouble in a little package, tears apart the rubber playmat, empties the toy box while loudly squealing with laughter, and crawls into and under anything. Meanwhile, Dottie, our quiet, more observant twin, is often found watching Olimpia trash the house, and if not that, she’s contentedly mumbling “dadada” to herself, while carefully exploring a silky tag on a stuffed animal for what seems like hours.

Their personalities show at the dinner table as well. Olimpia will eat anything you put in front of her, waving her arms from side to side, slamming her palms down onto her little tray, and kicking her heels with joy. Dottie will also eat anything, but is much more particular about it. She will insist on eating foods in a certain order (toast strips before yoghurt, thank you very much), and spends a lot of time staring off into the distance singing songs between bites.

In the past few days the twins have really begun to interact with one another, laughing maniacally as they catch each other’s eye. Their joyful cackles have replaced the complaining and whining that used to happen when I step out of eyesight; it seems now instead of missing my attention they are revelling in each other’s.

Their mutual ability to laugh is a way in which they are similar. Though they have different styles of laughter—Oli a high pitched squeal and giggle, Dottie a squeak and nasal snicker—they both get going and can barely stop. There seems to be no limit to the giggles their father can cause, with just a silly face or goofy voice. Now that they make each other crack up, it seems to be a constant sound rippling through the house.

Genetics are fascinating. At moments certain facial expressions remind me of my mother-in-law or my sister, my grandmother and my father. Parts of each of these people are in our little ones, not just in their looks but in how they express themselves and in who they will be as adults. I am curious to discover what parts of my own personality will be revealed in theirs. Perhaps what I hope they gain from me most of all is an ability to laugh at almost anything. In that aspect, we’re off to a roaring start.