Through the use of breeder documents.
Each culture/society has a process whereby identity is created.
It could be as simple as a naming ceremony or as complex as fingerprinting, DNA sampling and signing/notarizing forms from the parents and witnesses of birth.
These processes executed near birth for all humans create what we know in the identity management industry as "breeder documents". Not referring to humans as breeders, but referring to the documents as being used to "breed" additional identity documents as required by the individual.
These breeder documents are the source of all identity. It goes back to the birth of the individual.
Dr. Identity was created in 2001.
Marks of Identity was created in 1966.
The Obama Identity was created in 2010.
Identity Unknown was created in 1945.
A Case of Identity was created in 1891.
Defending Identity was created in 2008.
Cards of Identity was created in 1955.
The Obvious Identity was created in 1980-06.
Identity on Fire was created in 2010-10.
The Sword Identity was created on 2011-09-11.
False Identity was created on 1990-06-08.
The House of Lost Identity was created in 1927.