...The domestic cats are the only ones with eyes that slit. Eyes on big cats don't do that. I didn't realize that but am not surprised. It is believed that domestic cats originated in desert climates which tend to be extremely bright. The horizontal slitting of an eyelid coupled with the vertical slitting of a pupil combine to give remarkable control over how much light enters the eye. This pupil ability is probably more of an evolutionary adaptation to the environment rather than a characteristic of essential "catness". Domestic cats are also more likely to be polydactyl. This is probably also an environmental adaptation as it would make it easier to walk on sand, much as our snowshoes make it easier for us to cross snow. - Jack