Do most dogs treat people based on their physical apparence?

It is amazing what animals can do with their senses. To sum up, and add to, what others have said, dogs can:

1) differentiate people by smells. Some dogs may shy away from people because whatever perfume, deodorant, or laundry detergent is irritating

2) differentiate people by gender. A dog may shy away from a gender of human due to abuse by said gender before.

3) differentiate people by "vibes". I don't know how else to describe it. Perhaps dogs can see auras ???? But some dogs can just tell if someone is "not their type" or is someone to stay away from just by being near that person. It's odd, but a neat gift they have.

4) are perceptive to human emotions, such as fear, love, anger, etc.

One of our cats always hides from my husband's son whenever he's over. The son, 25 years old, has never done anything to the cat but be friendly. The son isn't aggressive, angry, loud, or anything. We have no idea why she reacts like she does and she's been doing it since day one about 7 years ago. Our other cats are just fine with him. *shrugs*