We want to believe we can change, that the we can become better human beings if we just make the effort. While change and growth are possible, my cats taught me that there is an underlying part of ourselves that is likely to remain the same over time: our temperament.

It happened when they first came to live with me. I was trying to decide what to call these two kittens who were brothers from the same litter. Since they had just arrived, I had shut them in the downstairs bathroom with their litter box so that they could adjust to their surroundings.

When I felt like things were quiet enough, I opened the door and then moved away from it, leaving them to decide when to come out. Almost at once, one of the two kittens poked his head out. He crept out and darted back, checking out his new home in stages. Of the other kitten, I saw not a thing.

Eventually the adventurous cat was roaming around the room, checking out places to hide and pouncing on things that looked like they needed pouncing on. Leaning forward, I could just see the other kitten, still in the bathroom, laying calmly on the floor and looking out through the open door, watching his brother explore.

That’s when it hit me: I should name these kittens after famous brothers. At that moment, they became Sherlock and Mycroft. The energetic, curious one was Sherlock and the one hanging back, Mycroft. For the moment at least, these names fit, since the famous detective’s brother was known for collecting information without leaving his rooms while Sherlock investigated things in person.

The observation that led to their names took just a few minutes. They hadn’t been in my home for an hour yet, but I had decided what to call them. It seemed a bold thing to do, to saddle them with such iconic names when I barely knew them.

By the time they were adults, it was clear that I’d named them properly. While both cats got big, Mycroft was the larger of the two, heavier than his brother, who continued to be the more active and playful cat. Mycroft hogged the food dish and Sherlock chased the elusive red dot. I’m sure that Sherlock did the lion’s share of the work when it came to keeping mice out of the house.

While I believe in change and growth, that we can become different and better people over time, Sherlock and Mycroft taught me that we also have underlying tendencies that may never change. In stead of being an obstacle to growth, our built-in temperaments and inclinations can be an asset. We just have to “know ourselves” (as Gretchen Rubin urges) and make good use of that knowledge.

Have you noticed traits that don’t change with time?