This can occur when part of a population of a species becomes separated from the remainder, they may over time evolve different characteristics from the parent population.

Both starch and cellulose are made by stringing together many glucose molecules, but starch is easily digested by humans, while cellulose is indigestible. the starch polysaccharide has every bond occurring below the sugar rings while the bonds in cellulose alternate between one bond above the ring and the next below the ring. how can you explain humans' inability to digest cellulose?