@Ceili,
Cats had both complex emotions and complex behaviors that benefit them.
To me both cats and human had this capability hard wire into us along with all higher mammals and for the same reason it promote survival such as the ability to be able to emotional bond with others.
When my youngest cat now wishes for my attention when I am on the computer she will begin to gently love bit my typing fingers!
A year ago, she had given up and stops eating because as the smallest of the litter she was not getting enough food to matter.
When I then placed her in a room with food by herself, she just look at it and still refused to eat.
The only way she would eat is when I placed the food in my hand for her and talk to her and love her up and as she eat the food she also would give my hand gentle love bits at the same time.
Her abilities to express emotions this complex and therefore bond with me is surely an evolution advantage of the first order for her.