In biology, you learn that every trait is on a binary. Then, you learn that there are exceptions to that binary, but most of them don't allow for a continuous range-- for codominance and incomplete dominance there are still only 3 possible phenotypes. But most traits we learn like that clearly don't fit into those categories. For example, we were told that hitchhiker's thumb is binary, you either have it (dominant) or you don't (recessive). But everyone who had it was a little different; some of the the thumbs were just slightly bent, some were very bent, and others were in the middle. But, this is not allowed from the binary that we are taught. That really confuses me. Or, for hair color. I know that both pheomelanin and eumelanin contribute to hair color. Everyone has 8 alleles for eumelanin that is either incomplete dominant or in incomplete recessive. This allows for 9 shades of hair color. Then, there is pheomelanin which is just regular dominant and recessive. This allows for 18 shades of hair color. I know for a fact that hair color has more than 18 shades. But, genetically, from what I have learned, there should only be 18. Am I missing something? Finally, just like the hitchhiker's thumb, many traits that are binary appear, by looks, to not be binary. It just feels like everyday obvious observations come into conflict with biology. I am definitely not trying to question biology, I just want to know if I am missing something, or if traits like hitchhiker's thumb are really binary. Thanks in advance.