Is the killing karma of animals heavier than that of humans?

Creating evil karma and killing karma is governed by the manas and carried out by the six consciousnesses. However, the manas's own independent mental activity is also a karmic formation, called mental karma (karma of the mind); it also stores seeds and also has karmic retribution, namely the suffering of birth-and-death in saṃsāra. Among the three kinds of karmic formations—body, speech, and mind—mental karma is primary and the heaviest, because bodily formations and verbal formations are directly commanded and controlled by the mental formations of the manas. When the manas gives rise to greed, anger, and delusion, the bodily and verbal karma thus created is called deliberate action; karmic formations not created by the manas giving rise to greed, anger, and delusion are called unintentional action. Deliberately created evil karma is great and deeply grave in its transgression, possessing inherent sin and inherent karma; evil karma created unintentionally is light in its transgression, lacking inherent sin and inherent karma.

When animals devour one another, it lies between intentional and unintentional; it is purely for the sake of hunger, without a mind to kill or a mind of anger and hatred, so the karma created is relatively small and the evil karma relatively light, without inherent sin or inherent karma—they simply repay their debts in the future when the debts come due. When one period of evil karma as an animal ends, one may be reborn as a human; if as a human one again creates evil karma, one will then go once more to the three evil destinies to receive retribution. In this way, sentient beings transmigrate through birth and death within the six destinies, and the karmic formations of the human body are the most crucial determining factor.