Humans do not come with good natural primary keys. Names are not unique and they change over time. In the USA we have a Social Security number which is tempting to use as a primary key. Do not use it! They make rotten primary keys for several reasons:

1. Not everyone has one.
2. Some people have two (or more).
3. Some numbers are used by multiple people. (Not suppose to happen, but it does.)
4. Many people think using the SSN is a civil liberties issue. They resent giving them out. They may choose not to give it to you. They may give you an incorrect one.
5. It is easy to forge.
6. In most cases, Federal law requires you to issue an alternative id to people who object to giving you their SSN. (For extra credit, register at your local Community College and refuse to give them your SSN. Can they cope? I did and mine can.)

So do everyone a favor and don't use the SSN as a primary key. If you need to store it, do so in a column that isn't the primary key.

PS. An exceptionally poor idea used by some banks and credit bureaus is to use the husband's SSN to record a couple's credit history. What will they do if they divorce?