There are some things that naturally makes us human and no matter the skills we May be deprived of or lack as younglings without proper induction of the human behavior into us by our Ward or parents they'd definitely still remain and one of them is that humans are generally Homo sapiens and no form of crudeness or growth in a place like a desert will take that away, however addressing your question constructively, I'll like to say If a child by some means survived and grew up in the desert without any human touch or nurture, a child might be emotionally, psychologically and mentally inept. For example attributes like having deep emotion when something like a tragic event that makes someone cry, they may definitely not express emotion or feel the sort of pain which sometimes is an artificial human attribute that can be learnt.
That is, such a child might not express things like courtesy, respect, orderliness and May be little edgy, untrustworthy and lack empathy. These are all attributes that we learn when we're exposed to interact with people in our society and since this child manages to survive in a lonely island or desert devoid of human, they won't be exposed to these virtues or values or behaviours which people pick up in places like School, Church or peer group events.
So the truth is such a child may just be 30 human depending on the age which they were rescued from such desert. If the person has grown into adulthood, I'm afraid the person may just be 5% human because the older they get in that place the harder their chances of adaptability when they're rescued.