Fact is, you are a unique information pattern in the world, defined by your mind, rather than just your private key.
How do you prove that you are you?

In mathematics, there is often a large number of ways to prove a fact if that fact is a universal truth. For example, there is a large number of ways to prove Pythagoras theorem. If something is true, you can look at it from many angles and arrive at the same conclusion. However, in cryptography, this hardly ever true. If you had lost your private key, you cannot access your assets, or decrypt messages, even if there is other strong evidence that they are yours.

The ability to prove things is critical to creating a world of fair credit and access to information. If you had ever lost a password, or wallet of bitcoin or other digital currency, or simply your data locked under your encryption key, you know how unforgiving is the fact that you only have one way to prove facts. For example, you may have proofs such as transaction records in other databases, governmental records and legal bank transactions, even people's memories, but that all doesn't count to recover a credit on cryptographic systems, if you do not have your private key.

Fact plain as the day of light remains: you are not your private key, and a multi-method provability of cryptographic facts about identities therefore would be a desired property for cryptographic methods.

Hash pill?

If the pattern that makes you - you, were to have the integrity of a blockchain, then you potentially could use the hash of your biological pattern at arbitrary moment, to provide a proof of yourself.

Question: does nature at physical level run on some kind of blockchain? The irreversibilitly of time may be an indicator that this is the case.

Question: Life is a process running on a much higher than physical level -- the expression of DNA also happens to be a computational process. Would introducing a substance (like a "CRISPR hash pill") to one's body, make a complex change in the further patterns that evolve in the body, that can be used to prove that the person had taken that pill before?

Biomarking yourself with a biomarker pill can work like something that binds a cryptographic key to a biological pattern forever. E.g., everyone who has a specific crypto-key, could log the proof of fact, when they swallowed the pill, in an existing blockchain, that tracibly binds them to that key.

Question: how hard would it be to fake those biological patterns, and what would the introduction of those patterns do to your very self?

Answer -- depends on the amount of information hashed at the moment of the bio-marker binding, and retained in the further evolution of the pattern that is you.