MRNA is called messenger RNA because

Our body is made up of different types of cells. ... All this means that specific cells produce specific proteins. Thus each cell requires to copy few specific recipes from the DNA stored within it. This is done by Transcription of genes on DNA to generate corresponding RNAs which are called messenger RNA.Jul 31, 2016

Explanation:

Cells of different tissues require to produce different proteins. This means that all the specific cells produce specific proteins. Thus each cell requires to copy few specific recipes from the dna stored within it. This is done by transcription of genes on dna to generate corresponding rnas which are called messenger rna

hope it helped

yes, because even though a theory has a  lot of evidence to support it, it is not always true