The mother of a child born outside of wedlock (presuming the father has not established legitimacy by court order), that mother has Sole Legal and Physical Custody rights as a matter of law, she already has "full" custody. The unmarried father must file to establish Legitimacy to gain any parental rights. Married parents have completely equal and undivided rights to everything "marital" including the children of the marriage. In a Legitimacy case or a divorce case with children, if the parents cannot settle their case by agreement, the judge will decide which parent will have Primary Physical Custody, the other parent will have Visitation rights, and typically the parents will share Joint Legal Custody with one of them designated to be the Primary Legal Custodian, which gives that parent the final decision making authority when the parents disagree about any legal custody issue. Most divorcing parents will come away with shared parental rights, so obtaining "full" custody is not generally likely, the same is generally true for legitimacy cases because the law presumes that legitimacy is in the best interest of the child. Thus, to obtain "full" custody in a legitimacy case or divorce case would require that one of the parents has very serious flaws, such that being around that parent would create an actual danger for the wellbeing of the child.
The "wrong" thing happens at the courthouse all of the time. The number one reason for that occurrence is that the person mishandled their case. The number one way people mishandle their case is they fail to retain an attorney to represent them. Other ways a mother may lose custody is based on mistreatment of the child, heavy drug and/or alcohol issues, perhaps DFCS involvement, and incarceration. Being found legal unfit will cause the same result, loss of custody.
It takes clear and convincing evidence for a court to find a parent "unfit" and to take away their parental rights. This can happen if the parent has abandoned the child, or has subjected the child to cruelty or abusive treatment, or is raising the child in immoral, obscene or illegal situations, and/or failing to provide the child with the necessities of life.
Legal custody has to do with which parent has the right to make important life decisions for the child. This is generally divided into 4 categories: medical, educational, religion and extracurricular activities. Physical custody has to do with which parent the child lives with on a fulltime basis.
Not so long ago this could be answered by saying "no" a judge will not grant 50:50 physical custody as the result of a trial. Back then, almost the only way 50:50 physical custody would happen is if the parents made a settlement agreement that included 50:50 physical custody and the judge approved it. However, in recent years some judges have ordered 50:50 physical custody in a contested case. It is still not the most likely outcome of a trial.
O.C.G.A Section 19-9-3, provides a long list of factors to consider. Evidence needs to be presented to address as many of these factors as possible.
These decisions are based on the court's determination of what is in the best interest of the child.