Does your pet “know” if you are a male or female?
I’ve known people who claim their dogs didn’t like men, for example.
I don’t know if they understand grand concepts but I know they how to differentiate. I have had dogs that had a bias towards one sex or the other several times. THe most obvious case was a male Alaskan Malamute that was a diehard female crotch sniffer. The nose knows.
My male pit bull puts his nose in a male crotch for about one second. He will keep his nose in a female crotch until he is forced to remove it. He’s tried to mount women who’ve come over to my house, but never men. I think he can tell the difference.
I remember reading some documentary about a woman who ran a wildlife sanctuary in Australia. One of its inhabitants was an orphaned male kangaroo who became quite attached to the lady and saw her as his mate. Whenever the lady was approached by a man, the kangaroo would become extremely agitated and have to be confined, or else he would come up and punch the living daylights out of the man. Apparently this roo was not in the least bothered if another woman came to talk to this lady, but it seems he saw human males as competition for his “mate”.
Oh yeah, and my own experience. My rats (all female) are very comfortable and social around women visitors, but become shy and evasive when men are in the vicinity. When one of my girls had babies, all the pups were fine being held by myself and other female friends, but when a male friend picked up one of the pups, it squealed in fear.
Cats can tell, They tend to prefer one human gender over another.
Like all animals, human males and females smell different. Female menstruation could possibly be taken for “heat”. (I remember a Pop-Up Video show which said during the taping of the video for “Like a Virgin”, Madonna was asked by the lion tamer if she was menstruating.)
Animals can probably also sense sexual immaturity in humans (pre-pubescent children smell different than adults) which is why children don’t usually trigger the jealousy adults do.
Besides the “stank”, human females and males have very different mannerisms, and domestic animals are extremely attuned to human body language. Males are louder and more bold, whereas females are more likely to cuddle and coo at the animal. In most homes, the male decidedly is alpha, even if the female is primary caretaker. (Ladies, how many of you have a dog who will jump to obey your man’s commands, but obeys you when it feels like it?)
But can they tell “those humans are male, those are female”? Maybe they just realize there are two types of humans, like the way we look at birds and insects. We can clearly see there are two types of peacocks, for example, but we don’t intuitively know if the ones with bright colors are male or female.
I don’t think I’ll ever bring up your question in the presence of my best friend’s husband. He always complains that their dogs ignore him and anything he says, while she can control the dogs with just hand signals. 
My dog tries to have sex with some of the women who come over to my house. He never tries that with any of the men who come over. I think that indicates that he is sensing and responding to a gender difference.
Maybe he just didn’t want the talent to get eaten.
I think some of us can understand this.