YOu know, all this mention of "fire" might be better replaced with "fire" when we are talking about the tool humans use and "oxidation reaction" when we are talking about the chemistry going on in our cells.
Maybe there could be some kind of weird group of chemicals at an high-energetic environment (say, a brown dwarf or even a star) that doesn't use fire but some other process that generates extra energy to do whatever needs to be done.
Well, Robert L Forward has written "Dragon's Egg", which discusses life on the surface of a neutron star. If I recall correctly, those creatures don't have a "biochemistry", as on the surface of the neutron star, what we think of as chemicals and molecules do not exist.
(Maybe a Sci-Fi writer might now get the idea of creating an alien lifeform that actually needs something to get rid of energy/heat, though i am not sure that such a tale would stand up to thermodyanmic considerations).
You already do - if your body did not shed excess heat, you would bake and die. Why do you think the summer is uncomfortable, and why do you think you sweat?
That said, the problem with "weird group of chemicals" is - chances are good these elements are more rare than carbon, oxygen and hydrogen, and thus life of that sort is less likely.
Well, silicon has similar chemistry to carbon, and seems to be pretty common. However, while similar, it is somewhat less varied in what compounds it will make. Boron has even more varied chemical properties than carbon, but boron seems to be pretty rare in the universe. But, you could at least imagine a silicon-based life form, instead of carbon based.
Not all Earthly life forms need oxygen for energy. But, systems that have an appropriate agent like oxygen to accept electrons at the end of the metabolic path are typically able to get more energy out of the same sources. It may be possible to substitute another chemical - like chlorine - to do the job. But, again, chlorine seems to be less common out in the universe, and chlorine has a stronger tendency to be bound up in minerals (salts, mostly), meaning it is tougher to build it up in an atmosphere.
We could also imagine life forms based on a solvent other than water - ammonia seems pretty common out there...
Isn't that also a reason why we cook food? Are we not able to bring the necessary energy to process raw meat? Or is it something else?[/SIZE]
When we started using fire, it wasn't that we were not able to bring the necessary energy to bear. However, use of fire has an effect we might consider... pre-digestion. Using fire makes it easier to access nutrients and calories in a great many foods. So, while we could bring that energy to bear, we didn't *have* to - cooking is more efficient. By cooking, we got more out of our food than animals that didn't cook, and that's a competitive advantage. We could get by with less food, or put forth greater effort on the same amounts of food we used to eat.
Now, humans have so adapted to cooking that we aren't really suited to eating a raw diet. We've lost some of the machinery - our intestines are comparatively shorter than those of other primates, our teeth aren't very impressive, and so on.
