In Biology, we are taught that human beings are made of 46 chromosomes. 23 come from the man. 23 come from the woman. The only creature that is possible through this is a human being. There is no other creature through with specifically that many chromosomes.
You may ask the question, why look at the number of chromosomes in a creature? The reason for this, is that this number is the most constant of any number in biology. There are other numbers that we could look at such as the number of bones, or number of teeth, but these have the ability to change and are not constant in every single creature.