Humane is a word designed to chastise people based on human societal morality. Humans evolved as a social cooperative species, and in a cooperative environment, selfish and exploitative entities are a drawback to others.

However, being selfish and exploitative of others is extremely useful for the entity behaving that way, as long as it is not ejected from that group.

The word humane is an expression of that ejection. Kindness, compassion and benevolence are good in a cooperative environment and benefit others and the whole group, thus we would like everyone around us to be "humane". Labeling this behavior "humane", good, and making the opposite, "inhumane" a very bad thing, serves to ensure these behaviors across a group of people based on societal pressure, thus making it more likely that people in general try to act humanely (or at least appear to).

Ultimately, every biological organism is entirely selfish, only "interested" (not in an actual conscious motivation kind of way, but in the total way they are built) in propagating its genetic material. Theoretically, in a cooperative context, the optimal way to achieve this is by taking resources from others all the time, giving nothing back, but having everyone else actually give. Obviously, that is not sustainable, since the giving entities will notice this behavior and thus stop their giving of resources. The result of that is a balance between selfish and altruistic behavior.

And thus follows, of course we all behave humanely and inhumanely. We are selfish and altruistic, some more this other more that. So yes, both behaviors are completely within human nature, the labeling of "humane" (i.e. someone who doesn't act humanely is disgusting, not even a human) is an extension of this struggle of getting everyone to behave altruistically, while selfishness exploiting that altruism is not a bad strategy.