There are huge tracts (some up to 730 bp long) of the *non-coding* mammalian genome that are ultra-conserved over 80 million years, without a single base-pair change. We share these sequences with rats, cats and apes. When these were discovered in 2004, people assumed they must play a role in regulating some important developmental genes. Now someone has made a knock-out mouse that lacks this sequence and – of course! – it is perfectly viable. There are no phenotypic differences at all… Weird or what?