If a baby is born with something other than two legs, that baby would be tested to see what has gone wrong in it's development. If you meet someone on the street who is missing a leg, you know that they have had an accident or have a health problem. You know this because we know that humans are meant to have two legs. These people are aided, because human beings are designed to move on two legs, we are bipedal. This is a biological fact.
Another biological fact is that we are a sexually dimporphic species - one category produces sperm, one category gestates and gives birth.
If a woman of child-bearing age cannot fall pregnant, she can go to her doctor and ask them to run tests to find out what is wrong. Why? becuase we know that under normal circumstances a woman should be able to get pregnant, and if she cannot then there is a problem. She could then hopefully be treated.
If a man had a problem producing sperm, he could go to his doctor and ask for tests and treatment. Why? because it is a fact that men should be able to produce sperm. If he cannot, there is something wrong.
If a woman goes to the doctors and asks them to test her to see why she is not producing sperm, will the doctor do it? No. Why? Because women cannot produce sperm. There is absolutely nothing wrong with her.
If I went to the doctors and asked them to investigate why I only have two legs, would they run tests? NO, because we are bipedal.
These biological facts are very relevant, yet they don't determine someone's value or 'validity'. Facts and values are different.