A spouse's sibling is the spouse's brother or sister by blood, and the spouse's marriage partner's brother or sister-in-law through marital assignment. In some cultures, such as those where inheritance is primarily through the male line, it can be difficult to distinguish between siblings and spouses. In many religions, such as Islam and Judaism, all children are considered equal before God, so there is no way to tell how God would view marrying your brother/sister. Since spouses share the same DNA, they are genetically identical: they will generally have the same traits, including a tendency to inherit diseases. However, because they did not share the same early environment, they may develop differently from one another. Their lifestyles are another factor that can influence how they appear today; for example, if one travels frequently, then they will look different from their spouse when they return home. In addition, since spouses marry someone else, they cannot be said to belong to each other any more than any other pair of people could. Spouses do not lose their own identities when they marry - they are still married even after one or both of them dies - but they become part of each other's families now. Finally, spouses are joined together by legal documents; thus, they can only be separated by death or divorce.