Nothing is permanent. Hardly anything is stable even throughout the entire human lifespan. No bio markers that can be easily scanned are reliably unique across a large enough population.
Email addresses are reliably unique (for a reasonably long time), which is why they are chosen for this purpose.
Phone numbers are now more "sticky" than they used to be and are now similar to email addresses at being useful identifiers.
Both emails and phone numbers are frequently lost, often at the same time.
Backup email addresses are the way to go.
Github does a good job at identity, I think, but they still use passwords (which are bad).
Email addresses are reliably unique (for a reasonably long time), which is why they are chosen for this purpose.
Phone numbers are now more "sticky" than they used to be and are now similar to email addresses at being useful identifiers.
Both emails and phone numbers are frequently lost, often at the same time.
Backup email addresses are the way to go.
Github does a good job at identity, I think, but they still use passwords (which are bad).