Hi, I'm not sure if this has already been reported and fixed in the repository version (20.x), but the following bug report was submitted for the CSharp Fork that I maintain: In the code below (from GeneVectorIndividual), you are attempting to fill "genome" instead of "newGenome" when the new length is greater than the existing length. public void setGenomeLength(int len) { GeneVectorSpecies s = (GeneVectorSpecies) species; VectorGene[] newGenome = new VectorGene[len]; System.arraycopy(genome, 0, newGenome, 0, genome.length < newGenome.length ? genome.length : newGenome.length); for(int x=genome.length; x< newGenome.length; x++) if (genome[x]==null) genome[x] = (VectorGene)(s.genePrototype.clone()); // not reset genome = newGenome; } Regards, Ben http://branecloud.codeplex.com