As an anthropology major, the study of humans, my approach to answering the question of “what makes us human?” will mostly employ the principles of anthropology, especially those of my “Evolution of Social Behavior” class, which I am taking concurrently with this one.
The first uniquely human trait is the capacity for cumulative cultural transmission of information. This is the ability of techniques and information to not have to be relearned every generation, but rather built upon to reach new discoveries that would not be possible within the lifetime of an individual were s/he to start from scratch. In my opinion, this single trait is what has allowed humans to advance further than any other species in terms of technology.
In order for cumulative cultural transmission to work efficiently, there has to be a shared code that information can use to be transmitted. This brings me to the second uniquely human trait, language. Although other species may use certain sounds, signals, or songs to indicate important things, humans are the only known species that have a widely complex system of grammatically-correct noises that can express even non-essential things. Further, this system varies by ethnic group.
Finally, humans use cooperation more than any other species to form multi-scale, multi-tiered alliances, helping each other extensively even when there doesn’t appear to be a selfish reason. This is because humans have the cognition and memory to be altruistic, rather than just using direct reciprocity like most other species. In addition, the alliances can be much larger than those of any other species, in the form of large-scale groups like nations and religions.