You probably know the classic three answers to that one: humans are unique among animals because of tool use, symbolic behavious (e.g. language), and the domestication of other living things. Now, however, we may be able to add a fourth… although it might be better understood as the one that underlies and informs the other three, namely our long history of learning about and understanding the behaviour of other animals. Take it away, Ars Technica:

Shipman asserts that humans’ invention and use of stone tools about 2.6 million years ago helped them successfully hunt and quickly dispatch large carcasses, allowing them to become major players in the predatory guild. As a result, humans became much more in tune with animals for two reasons: the better they understood their prey, the more efficient hunters they would be, and the better they could evade and outcompete other carnivores. Thus, the animal connection began; because it enhanced survival, learning about animals’ anatomy and behavior became a very advantageous pursuit.

The animal connection is strongly evident in another trait that is considered unique to humans: symbolic behavior, specifically art. Animals were the main subject of prehistoric art. Incredibly specific details can be recognized from early cave drawings, including animals’ colors, particular behaviors, and dimorphism between the sexes.

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Finally, Shipman claims that by domesticating animals, humans used them as “living tools.” Evidence shows that dogs were the first animals to be domesticated, suggesting that the first domesticates were not used as food sources. In early societies, animals served many purposes, such as carrying heavy loads, providing raw materials such as wool, producing fertilizer, protecting people, hunting game, and transporting goods. By using their accumulated knowledge and understanding of animals, humans were able to transform other species into “living tools” that enhanced their own fitness.

I think we may just have retrospectively uncovered the artistic statement embedded in the Tardigotchi…