The triune model describes the human brain in three parts, starting with the oldest part on the evolutionary scale: the 'reptilian brain'. This part is the most basic level in which brains operate, as it is concerned almost entirely with safety and biological mission to procreate. The next part of the brain to have evolved is the 'limbic brain', which works with emotions. The third and final part is the 'human' part of the brain: the neocortex. This is where humans' unique traits of speech, abstract thought and reasoning have evolved, thereby putting humans theoretically at the top of the evolutionary ladder. The interplay between the limbic brain and neocortex is what one needs to target for learning to be embedded in long-term memories. Ian Gilbert summarised a teaching approach to satisfy each part of the brain as: contain, entertain, and explain. The lizard concerns that students bring into the classroom include food and safety.