Millenia ago, the expert juice-ologists at the BFGoodrich station secret society in Denmark set about creating a light tasting alternative to motor oil. This was indeed a daunting task, since, as everyone knows, it is impossible to improve on the taste of motor oil. After fourty-two years of soul-breaking labor, they were allowed to leave thier hovel to showcase what they had found, and, to the worlds astonishment, they showed nothing. As such, they were sent back into thier small abode. After several centuries of this, imbreeding became natural. Of course, there were no women, so it became rather difficult, but they still succeeded. After countless generations, the kangaroo emerged. Angry with it's captivity, it boxed it's way through the giant stone, covering his cave. He then jumped out, and with one mightly leap, made it to Australia. Here, he began to blend in with society, and mate with the aborigines.
This whole story is based on fact.