Hello, The valadity test for this task has a bug. Complete code is not allowed, so here are the key points : Here are the constructors I used (second constructor calls the first one with null argument for father and mother). 
public Human(String name, boolean sex, int age, Human father, Human mother){
    this.name = name;
    this.sex = sex;
    this.age = age;
    this.father = father;
    this.mother = mother;
}

public Human(String name, boolean sex, int age){
    this(name, sex, age, null, null);
}
Here are the 4 objects with no father and mother that I created (this worked and was considered a correct solution) : 
Human GF1 = new Human("GF1", true, 90);
 Human GF2 = new Human("GF2", true, 87);
 Human GM1 = new Human("GM1", false, 80);
 Human GM2 = new Human("GM2", false, 88);
etc... (5 objects with non-null father and mother)
However, the first time around, I had created these 4 objects instead (identical to the other solution, but was considered NOT correct) : 
Human GF1 = new Human("GF1", true, 90, null, null);
 Human GF2 = new Human("GF2", true, 87, null, null);
 Human GM1 = new Human("GM1", false, 80, null, null);
 Human GM2 = new Human("GM2", false, 88, null, null);
etc... (5 objects with non-null father and mother)
With the second solution, the condition "Create 9 different Human objects (4 objects without a father and mother and 5 objects with them)." was not validated (although is was clearly met as much as with the first solution).