one of my greatest confusions of "life" is why there is this need to consume or feed off of or battle against other life. what is the purpose of this drive? why is it like this? i suspect the answer lies in thermodybamics and/or information theory, but it would be amazing to understand the reason behind life's battles for survival.
My friend built a house. I wanted a house. It was easier to take the lumber from his house than cut down trees and mine iron for nails. Eating another is no different. Different life evolves to take a niche item (like grass or minerals) and turn it into something useful to them (muscle and fat) that is also useful to others.
Are there really that many other ways? Photosynthesis, sure, but that doesn't seem to produce much and doesnt allow much "liveliness".
Anyway...
The 'why' is trivial-seeming to me. Once one organism can consume ready-made nutrients from another organism for less energy cost than producing, it will, or it will be out competed by others who do. So carnivores exist everywhere. Even deer happily eat baby birds that they come across, and rabbits eat their own.
Because the amount of energy that is available increases the further down the food chain you go. Photosynthesis provides a small amount of energy, hence why plants and plantlike organisms tend to be either totally stationary or don't move much on their own.
Organisms that consume plants are capable of more complex behaviour and growth because the amount of energy and nutrients etc. is greater that they receive by conauming things that photosynthesize.
the analogy seems fine to me, if a bit anthropocentric.
every living organism has some way of perpetuating itself, either by growing indefinitely or by making copies of itself. there's no reason "why", other than that organisms that can't do this get filtered out very early in the game. this implies having some sort of "strategy" for traveling up the energy gradient.
short of somehow evolving the biological capability to fuse/split atoms, all the usable energy on earth comes from the sun. so the first link in the chain has to be something like photosynthesis, where you collect and store energy directly from the sun (ie, "building a house"). but in doing this, you change the gradient, creating an opportunity for other organisms take your stored energy for themselves. in some sense, it's much "easier" for a rabbit to eat a plant in one minute than it was for the plant to collect all that energy over its entire life. there's only so much solar radiation per square meter, which limits a plants energy budget. a rabbit can eat many plants in a day, effectively multiplying the area of the solar radiation it can capture (and spend on acquiring even more). but then the rabbit creates an opportunity for a predator to harvest its stored energy and the cycle continues...
it seems like you're maybe asking "why can't all life just cooperate"? this would probably look like a planet full of plants (or a similar lifeform at a different scale). the problem is that this leaves a huge opening for the first "defector"; it's an unstable equilibrium. life does not evolve to leave opportunities on the table.
Look into "dissipative structures", which are indeed closely linked to thermodynamics.
In short, energy gradients (ie, on hydrothermal vents) can cause matter to organize itself into structures that more efficiently dissipate this energy. You can see how the creation of this structure would in turn enable the creation of a new kind of structure that lives on top of that.
There are competing processes in nature even without life (in the usual sense of the word) - atomic nucleus fission/fusion, light absorption/emission, crystal nucleation vs. decay, molecule synthesis vs molecule decay - each process operating towards getting more ground. Life fighting (or helping) other life can be looked upon as a more complex variant of the same process dynamics: one set of atoms and processes interacting with other set of atoms and processes, sometimes this looks like cooperation, sometimes like a battle.
Actually game theory is probably the better place to look. Though the concept of natural selection already tends to cover the big picture. Organisms need resources to reproduce. Those that can obtain more resources (or use what they have more efficiently) reproduce more and eventually drown out those who cannot reproduce as much. Taking from another organism (whether by hunting, parasitism, etc) is just one way of obtaining more resources.
Thats probably the thing I learnt looking through the microscope, or was perhaps made obvious. Life at that level is just chemical gradients and finding bio mass to procreate, so things that don't do this don't procreate and die, the winners are the ones that are the best at this. The asking why is a human thing and is so many layers on this elementary life we can afford to ask these questions, but I don't think life can exist without competition, at least not organic life that has evolved. Maybe we'll make a more pure sort of life that doesn't need competition to grow but not sure about that.
