Originally posted by Symmetric Chaos
Traditionally the separating aspect is the soul, language, tool making, fire or agriculture.
The soul aside, all of those, with the exception of language maybe, are more an example of "culture" rather than specific "things" that separate man from animal. We also have computers, cars, electronics, etc, but those all might indicate another underlying principal of the human mind.
One of the things that does make us human is our ability to imitate. Not mimic, but to see someone's action, and be able to ascertain the meaning behind why they are performing said action. So, I could watch you turn on a light switch with your foot because your arms are full, I would not think that I needed to copy the motor action of flipping the switch with my toe, but would understand that the light is turned on by the switch, which you are trying to hit. Few animals outside of the greater primates have this ability.
I tend to believe this, plus an innate drive to imitate others, mixed with some joint attention, underlie most cultural developments. Agriculture and to some extent fire might be different, because they fundamentally changed the nature of human life, but the concept is the same, and it is hard to claim agriculture as a human phenomenon when some cultures (largely destroyed by more technologically advanced cultures) never developed sustainable agriculture, and many that did, simply imitated a practice developed in the fertile crescent.
Language becomes more difficult, because it, imho, does go beyond simply taking advantage of our joint attention/mirror neuron systems, and the brain actually has to use a statistical probability of sound patterns to decipher what such verbal symbols mean, and how to generate meaning from those sounds. I believe language probably evolved from our ancestor's imitation system, and might be best described as innate, passive, involuntary imitation on steroids, though even then, I would consider language special enough not to claim it to be entirely a cultural imitation, and consider it a separate part of the human condition. Other cultural things, like fire, agriculture, or tools, seem, to me, to represent our imitative ability, which is far and above any other animal, though, other primates do share the ability to pass along items of culture.