Jiva is written in Scala, a very powerful OO/Functional hybrid language that runs on the Java Platform: http://www.scala-lang.org/
Jiva started out life earlier this year as a GA toolkit written in Java. I decided to port it to Scala because I figured that this might be a good way for me to (a) learn Scala, and (b) have some fun in the process. And I think this has turned out to be mostly true (especially the fun part!).
I should point out that despite its early-release status, Jiva is pretty functional (http://code.google.com/p/jiva-ng/wiki/FeatureSet ). If you are interested in playing with Genetic Algorthms, I encourage you to give Jiva a try. If you run into problems or have questions, please let me know.