Hi, 0. Be sure you're using the SVN repository version of ECJ, not the tarball version. ---> Yes, its from the SVN. 1. You seem to have a hard wrap in your text file below, breaking the genomes into two lines. ---> No. That's only because the genomes are long. So it appears to be hard wrapped when I paste into this forum's editor. 2. Ignore the first once-only warning. ---> Ok. 3. The file below has two individuals named "i2|". That's the cause of the second warning. ---> If you are referring to "Individual Number: i0|", there are no duplicates. 4. I can't tell what's going on with your null pointer exception, it's inside your code, sorry. ---> Ok. 5. PrintIndividual needs the EvolutionState because it needs the Output facility. Is there a reason this won't be available but you'd still want to print printIndividual? You can recreate most of printIndividual by just writing out the right text and the right genome encodings (use ec/util/Code.java). ---> I want to quickly test ECJ with an initial population to see if its what I need, without having to dig for days simply to understand its workings. If you have a simple example, that would be very helpful.