When I was in middle school I first learned the basic idea of the fundamental theorem of arithmetic and my instantaneous first idea was that we should assign a unique prime number to each attribute that a biological entity can have, and then multiplying together the prime factors for all the characteristics would give the unique integer ID for that biological entity.

So if having a limb is “7” then some creature with three limbs gets 7^3 in its prime factorization, and so on.

Obviously it is an incredibly stupid idea, but 12-year-old me was quite impressed by the thought of it.