# Biology (life science) explained

Every living being has a few universal characteristics:

- Sustained by consuming a substance that is then metabolized into energy (that energy measured in calories).
- Consumes some type of gas that transfers carbon into or out of the organism.
- A means to make some form of [decision](people-decisions.md), even if it's a rudimentary impulse.
- Some form of "skin" that establishes a clear [boundary](people-boundaries-why.md) against the surrounding environment.

Further than that, there are levels of sentience, with each level having the elements below it as well:

1. Survival reflex mechanisms (e.g, mollusks, jellyfish)
2. Complex behavior suggesting higher sensory awareness (e.g., most fish, reptiles)
3. Demonstrates communication and caregiving (e.g., cows)
4. Evidence of planning and vicarious learning (e.g., big cats)
5. Flexible behavior including tool use or [language](language.md) (e.g., most birds, octopi)
6. Problem-solving with rudimentary social understanding (e.g., parrot, dog)
7. Evidence of self-awareness adn behaviors that aren't always linked to survival (e.g., elephants, dolphins)
8. Basic theory of mind, more complex and [creative](mind-creativity.md) behavior (i.e., primates)
9. A complex theory of mind with the capacity for metacognition (i.e., [humanity](humanity.md))

In many ways, the structures that form life are akin to remarkably well-designed [technology](technology.md), with many built-in redundancies and fail-safes.

## Obvious unanswered questions

- How did life begin?