The phrase what it means to be human can be elaborated in two rather divergent senses, depending on whether the opposite of "human" is taken as "inhuman" or "non-human". The first path, of course, is what humanism is all about. It starts from the premise that people can be taught to respect all their fellows and act in consequence.
If, on the other hand, you consider how the human species has distinguished itself, in the past, from the rest of the animal kingdom, you are obliged to admit that they used the ressources of their superior brain mainly to plot and scheme against each other (forming selective and temporary alliances)...