why is evolutionary theory constantly changing?

Please define "recently". For at least a number of years (more than 10) I seem to have been reading about chimps being closer to us than any other animal. I think bonobo's have only been uderstood to be separate for a decade or two.Chimps are apes. So I presume you mean gorillas or something. What is your most recent reference for they being closer to us than Chimps?The details have only been sorted out (I think) since we could examine the genetics. So the current ideas wouldn't be older than a few decades.

I'm not sure that "ape" is a formal classification but I do know that the "great apes" are considered to be gorilla, orang, chimp and bonobo.Primate is a formal term I think and the gibbon is included in that as well as humans. hmmm it seems the monkeys are included in there too.