Why did humans leave Africa in the first place? Their migration could have been sparked by competition, climate change or simply a great hallmark of human nature, curiosity. Over the past 2 million years humans have proven to be a remarkably successful species. In fact, humans are the only species on the planet with a global distribution. In order to figure out how we might fare in the future with a changing planet, it's critical to get insight from our past. Link: The 2 Million Year Melee: Neanderthals vs. Humans