I don’t think this will come as a surprise to anyone, but the experiment still had to be done. It’s nice to know that genes conserved over millions of years are conserved because (gasp) losing them is bad for you.
Seriously though, this is a very nice paper. As they say:
Almost all eukaryotic genes are conserved, suggesting that they have essential functions. However, only a minority of genes have detectable loss-of-function phenotypes in experimental assays, and multiple theories have been proposed to explain this discrepancy.
They show then that almost genes have significant effects on fitness if you just measure it properly. Take a look: