The fact is, siblings really can grow up to be opposites. Even identical twins. It’s impossible for two people — any two people — to have exactly the same experiences from the moment they’re born. Different life experiences develop distinct personalities.

According to Gerd Kempermann, a behavioral geneticist at the Dresden University of Technology and the German Center for Neurodegenerative Disease in Germany, an experiment with mice demonstrated that even genetically identical animals behave differently. These differences grow with time. So, it’s no wonder that Alexandria and Jessica’s age gap had such a profound effect on how they look and live now.