In simple terms why doesn't all mutations cause a change in an organism?

o Because of synonymous mutation. If you look at your genetic code chart, you will see that some amino acids are coded for by several different codons. A synonymous mutation will change from one of those codons to another, so the amino acid in the resultant protein will not change.

o Because of neutral mutations. Plenty of our genome is noncoding. Some mutations in some of these areas won't cause any perceptible changes.

Mutations happen to individual organisms. Natural selection decides if that mutation is good or bad, and the mutant either breeds and becomes a new species, more advanced than before, or dies out due to the mutation holding it back.

Thank you. :)