So, what is the Sixth Extinction? When is it coming and what is its cause? It is happening now, and we, the human race are its cause explains Richard Leakey. This phenomenon Leakey argues, is easily comparable with the big five biological crisis' of geological history, except this one is not being caused by global temperature change, regression of sea level, or asteroid impact. It is being caused by one of Earth's inhabitants. According to Leakey, humanity is poised to become the greatest catastrophic agent since the giant asteroid, which collided with Earth some sixty-five million years ago, wiping out half the worlds speci