microsat

I am just wondering how we call this theory as neutral theory if it asserts majority of mutations are deleterious or slightly deleterious and these deleterious and slightly deleterious mutations should be determined via the fitness of the NATURAL SELECTION. Does anyone know what neutralists and selectionsit think respectively about what proportion of all mutations is adaptively neutral, deleterious(lethally and slightly delterious), and advantageous, respectively? What's the difference of their thoughts about the mutation proportion question?

"The neutral theory of evolution (Box 1) is the accepted null model for the evolution of DNA sequences. It postulates that the vast majority of nucleotide sequence differences observed between species do not affect function, and that many or most mutations in nucleotide sequence are deleterious and therefore subject to negative natural selection. Therefore they never (or only rarely) come to fixation. An alternative possibility, which might apply at the phenotypic level, is that most differences between species are adaptive and fixed by positive selection. " excerpted from http://www.nature.com/nrg/journal/v7/n9/full/nrg1940.html How to understand the above paragraph from NATURE REVIEW. Is it correct or wrong? Does neutral theory assert that majority of mutation are deleterious? If it does, how to measure if a mutation is 'deleterious' or not?