Merging objects from two list with unique id using Java 8

class Human {
    Long humanId;
    String name;
    Long age;
}


class SuperHuman {
    Long superHumanId;
    Long humanId;
    String name;
    Long age;
}

I've two lists. List of humans and List of superHumans. I want to create a single list out of the two making sure that if a human is superhuman, it only appears once in the list using java 8. Is there a neat way to do it? UPDATE: These are different classes i.e. neither extends the other. I want the final list to be of superhumans. If a human already is superhuman, we ignore that human object. If a human is not a superhuman, we convert the human object into the super human object. Ideally I would want to sort them by their age at the end so that I get a list of superhuman sorted by date in descending order.