If a single base pair gets damaged and goes missing from an rna, what would most likely happen?

A frame-shift mutation would occur. This is because a deletion will cause a change in codon sequence from the point of mutation to the end of the mRNA.  If the mutation is closer to the start of the mRNA, the larger the effect of the mutation on the translated protein.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".