Here is A Question. or two...?

Rats are like humans in many ways. and they have helped us learn a lot about the human race and life through lab results. because they are super close to us. so were told that we share dna with rats. than how do we share dna with monkeys? how come the theory of evolution states that what ever we evolve from must die, than how come there are still primates? is it similar with cats and dogs? dogs and cats are super a like, but they are not the same beings. they are not related.