Answer:
It is due to the differences in DNA sequence and collection of genes with the exception of twins, triplets, and such. That said, the attainable sequences are exceptionally colossal but should not be infinite. That aside, considering the number of words there are in the English alphabet with only 26 letters, has 171,476 words and counting (around 800 to 1,000 new words are created every year according to Global Language Monitor-GLM).
