I have yet another The Emigrants theory
Before I start, I want to say that you don't have to like/read The Emigrants to read my theories or just anything I post regardless this book series, so feel free to answer and read them
Ok. In the Prologue, Karl was 19 and he lived with his dad. His dad, a man named Nills (That's why Karl's last name is Nilsson) was basically very injuired and because of that Karl had to take over the farm and stuff
Well Guess what
There is a scene where Karl's dad helps Karl repair his new house when he married Kristina
For those who are confused, after the prolouge and a few pages after the 1st chapter there is a section of what happened before the 1st chapter. Appearently, this was when Karl and Kristina had their first 2 children, Anna and Johan.
well, Karl's dad was helping them to renovate their house to make enough space for them.
Then the dad dies in the latter Chapter 1, and so Karl and Kristina live with Kristina's family and their children.
So Either the dad was faking his leg injury (which he wasn't, a rock fell on him) or he was very strong (So you see, That's how Karl became inmmortal)
But that's just a theory
a book theory