It might shock you to learn this, but DNA doesn't come into the picture for most people getting married in Australia. It's what's on your birth certificate that counts.

There's a simple legal reason for this. It's called legal presumption of parentage.

Presumption of Parentage

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The law says a person is the child’s biological mother if they are named as the mother on the birth or adoption certificate.

The law says a person is the child's biological father if:

• they are named as the father on the birth or adoption certificate
• they acknowledge they are the father by providing a statutory declaration or affidavit
• they were married to the child's mother at the time of birth
• the child was born within a defined period after the parents lived together

All other relationships, including prohibited relationships (those people you are banned from marrying) flow on from this.

Evidence

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When a child is born, the hospital is responsible for issuing a certificate as to who you are (name, date of birth, where you were born, presumed parents, and who witnessed/attended the birth. The information on this certificate is what is entered in your birth record. Where a child is born in other circumstances, for example home birth or in the back of an ambulance, documentary evidence is still required.

Most people are confident who their mother is. Though in days gone by it wasn't uncommon for an unmarried woman to check into the maternity ward pretending to be her married sister, record keeping that lies behind Medicare, for example, makes that less likely. But that's not to say that registering a birth is plain sailing in every instance.

Adoption

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Legal adoption changes legal parentage. A quirk of Marriage Law to do with prohibited relationships is that, even if your adoption was rescinded, even if you were then adopted by another family, anyone in your first adopted family who was, by adoption at that time deemed to be an ancestor or a sibling, is forever banned from marrying you.

Parent Unknown or Left Blank on your Birth Certificate

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There are a number of reasons why a parent (usually the father) is not recorded on your birth certificate

• Parent is genuinely unknown
• Parent was/is known but did not legally and formally acknowledge that they are the parent
  
• Your parents were not married
• Your parents did not meet the de facto requirements
  

What does this mean for Your Marriage Certificate?

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Occasionally I have a couple getting married where one of them is confident that they know who their "real" father is. Usually because they have been told by family members. Who could, not to put too fine a point on it, be wrong, or even deliberately lying.

Even if you are confident you know who your father is, unless you have a determination from a court of law, generally based on DNA testing that complies with the regulations outlined in the Family Law Act 1975. you cannot have your birth certificate amended. And, unless the name appears on your birth certificate, it cannot be recorded on your marriage certificate.

What does this mean for who you can or cannot marry?

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Actually quite simple. You can't marry anyone who is your legal ancestor or sibling, and any child you have had.

Anyone else is okay. So you can marry your first cousin, even though in many countries you can't. And you can also marry your uncle, aunt, regardless of whether they are a sibling of one of your parents or an unrelated aunt or uncle by marriage. And you can marry your nephew.

Thanks for reading!