If you model rabbits under ideal circumstances, you may find that the number of pairs of rabbits each month follows the Fibonacci sequence.
In this case, ‘ideal circumstances’ is a euphemism for nonsense, as your assumptions would include blatant untruths such as “rabbits mate once a month every month except their first month alive”, “a pair of rabbits gives birth to exactly one pair of rabbits per month”, and “the hutch is infinitely big (and hence Starsky is very squashed)”.
Fibonacci numbers, however, are not completely absent from nature. They accurately describe a vastly superior animal: the honeybee.
Male bees (drones) come from unfertilised eggs, and so they only have one parent — the queen.
Female bees (workers or queens) come from fertilised eggs and so have two parents — the current queen and a drone.
If you follow a drone’s family tree backwards, you will see that a drone has:
The number of ancestors of a male bee follows the Fibonacci sequence.
Who would’ve expected that?!