Re: Do humans ever in their lives have gill slits because we are vertebrates

Good question. No, gills do not appear at any stage of mammalian 
development. Some amphibians do go through a stage of gill-breathing, 
however. 

We have an evolutionary remnant related to our having gill-breathing 
ancestors, however, as jaws developed long ago from bony gill support. This 
happened long ago in certain fish. Lungs also first developed in fish, but 
the are derived from the swim bladder, not from the gills.