Final answer:
The definition of an inborn biological force that determines behavior is instinct, which is an innate behavior, occurring naturally without learning.
Step-by-step explanation:
An inborn biological force that determines behavior is the definition of instinct. Instinct is classified as an innate behavior, which is a natural, unlearned response to stimuli and has a strong genetic component. Unlike learned behaviors such as habituation or conditioning, instinctive behaviors occur naturally in all members of a species and do not require prior experience or environmental influences to emerge.