Every kind of living creatures has a kind of DNA. The nucleotide bases from which DNA is built are A (adenine), C (cytosine), G (guanine), and T (thymine). Sometimes if two DNA of two living creatures have the same substring, and the length is beyond a certain percentage of the whole length, we many consider whether the two living creatures have the same ancestor. And we can separate them into a certain species temporarily for our research, and we say the two living creatures are similar Make sure if A is similar with B, and B is similar with C, but C is not similar with A, we also separate A, B and C into a kind, for during the evolution, there happens aberrance.
Now we have some kinds of living creatures and their DNA, just tell us how many kinds of living creatures we can separate.