Do most dogs treat people based on their physical apparence?

Dogs judge people in many ways. They pick up on your smells, your mannerisms, how you are holding yourself. I don't think it's so much male or female but a combination of many factors. If you speak loudly or make too much eye contact with them, this might be intimidating or cause fear.

I have a small dog (9 lbs.) who is afraid of strangers. She loves everyone in the family, male and female. However, she is terrified of my older brother. He has never harmed her and always tries to befriend her. For some reason, he makes her shakes with fear. She hides when he comes over.

He does have a loud, gruff voice. Sometimes he is in a grumpy mood. I think she picks up on these clues and it unnerves her.