Philosophers have been discussing their versions of the purpose of life for as long as philosophy has been recorded. Almost all of them grew up in an environment of beliefs in magical creatures, and while any particular philosopher might have abdicated his belief in them, they set the background for philosophical discussions. Perhaps now, in an environment where scientific beliefs are becoming more prominent, and perhaps dominant in many minds, some different thoughts can be found.
Life is the collection of life forms present on planet Earth, Having a purpose for life does not mean having a specific purpose for every single amoeba, virus, insect and crustacean, but for some fraction of them, perhaps a negligible fraction. People are a part of Life. Having a purpose for human beings, or some portion of them, would constitute a purpose of Life, even though the mass of protoplasm included is fairly small compared to the total.
Purpose is a goal involved in the design, production, manipulation, use, or even disposal of an object or collection of objects, as stated or implied by the designer, producer, manipulator, user, or disposer of whatever is under consideration. An obvious place to start is with this person, although if a computer were smart enough, it might develop a purpose for something. Any intelligence should be sufficient to create a purpose.
Finding a purpose when the originator of the purpose is mum on that account might be done if there is only one thing that the object can do. A subway train is only good for moving people from one stop to another, so it is a safe bet that its purpose, as dreamed up by the original person who though up the concept, and likely everyone else involved with any subway anywhere, that this is what its purpose is and was. When something has more than one purpose, the question becomes more difficult. Pick-up trucks might be used by one owner to haul building materials, by another to commute to work, by another to race other pick-ups, by another to bring to car shows, and so on. The purpose of a multi-purpose object is defined by the person using it, which might be the owner, or renter, or inheritor, or thief. Since many things might be involved with many actions, finding out who is entitled to dictate the purpose is a good first step. This requires fleshing out the definition of purpose a little better.
If an object can be possessed in some legal sense, according to the laws present contemporaneous with the validity of the determination of purpose, we ask the possessor what the purpose is. If the owner of a particular pick-up truck says it is his goal to use it in auto shows, then that is its purpose. If the renter of a pick-up truck says he rented it to carry drywall from the store to his home under construction, then clearly its purpose, for the duration of the rental, to haul drywall. This is fine as long as there is some social construct which focuses down on one individual who can be asked what the purpose is, or observed in using it so that the purpose can be deduced. We have essentially passed off the question of purpose to another person.
Someone might simply answer that a particular object has two or more uses, and then it has two or more purposes. There is no one-to-one relationship between a useful object and a purpose.
Things get slightly more tricky if there are multiple owners for the object. If two partners own a pick-up, one can have one use for the time he has it, and the other, another use or purpose. If it is a large group of people who own something, then there must be an executive in charge to define the purpose or purposes of the object. This problem melts away for something like a subway, which has only one conceivable use. Its purpose to move people from one stop to another, no matter who owns it. The reason for this is that no matter who it was who has ownership of it, or who designed it or came up with the concept, there is no getting away from the fact that it only has one use.
Let’s now begin the descent into the nether world of non-owned things. Without an owner, or some other person or intelligence able to define a use, does anything have a purpose? This is tautological, as we define purpose as the design goal or goal of the current controller. It is a meaningless question, and cannot be answered without altering the definition of the word purpose. All the aeons of philosophizing has been about carefully redefining the word without actually explicitly defining it clearly enough to recognize what has happened.
There is simply no purpose for anything that does not have someone entitled to present it with its purpose. That may be a collective entity such as a corporation, as long as someone with it has been given the task of using or controlling it. Other things have no purpose. One could ask, what is the purpose of the moon? There are many things that the moon does, such as tides, moonlight, a destination for Apollo astronauts, serving as a target for asteroids, gravitationally slowing the Earth, and so on, but none of these was used in the process of creating it, as it was not created by an intelligence, but by complex physical processes.
If someone were to come up with a creation myth involving magical creatures, one could say that within the context of this fantasy, there is a purpose, but outside of the fantasy, there would be none. It is certainly possible to do the same with the sun. The fact that the sun is responsible for the energy source that drives photosynthetic creatures and creatures which feed on them, which incidentally is almost all of what we defined as Life above, has no bearing on the definition of a purpose for the sun. One could pretend to forget about the fantasy of someone creating the sun and say that its purpose was to provide energy for Earth’s life, but this can only be done by altering the definition of the word purpose. The purpose of a nail is not to give the hammer something to strike. It is to accomplish something subsequent to its use. The word to use for what the sun means to life on earth is to say the utility of the sun for life on earth is to provide the large majority of its energy.
What is the purpose of Life? For Jadav Payang, an Indian who has spent about four decades planting trees on an island in the Brahmaputra river for the purpose of preventing further erosion of the island, the purpose of life is to prevent erosion, or at least of one island. He has been remarkably successful at it, and he has used living organisms for a purpose, even though he does not own them and has not created them. He has become the controller of the trees involved to a limited degree, and although he relinquishes control of the trees once they are planted, he has them when they are being put to a use, and that is the critical time for the definition to function.
One could say that a farmer or a rancher puts life to use, and therefore provides a purpose to life, by using it in the process of providing food for humans and domesticated animals. A cell biologist uses life for his own purposes. One could say that people use themselves, and therefore give themselves purpose. In times of slavery, the owner of a slave might provide purpose to the slave, thereby providing purpose to one small bit of Earth’s life. The developer of a vaccine utilizes live bacteria to make the vaccine, at least some vaccines, so he provides a purpose to an even smaller bit of life.
So, it can be said that life has multiple purposes, and many individuals are involved with providing these purposes. However, there is no generalization possible. Just because some small bit of life is given a purpose by human individuals, there is no overall purpose that can be derived from it. Perhaps one could argue that serfdom is a type of ownership, and the Russian czars provided purpose to the millions of serfs in the Russian Empire. One could even stretch that argument and say that any empire has a leader who provides purpose to the empire’s subjects. Perhaps a general can be said to be providing purpose to the soldiers under his command.
These political and military hierarchy examples weaken the definition of purpose, however, in that the leadership only provides broad orders to those underneath, and then these are all elaborated on as the order is implemented downward. It is becoming fuzzy, but one could also say that the empire or army is collectively providing purpose to itself.
There have also been theological hierarchy which have held sway over large numbers of humans, but without a military or political hierarchy to provide the means to enforce an order given by a theological leader, it so further weakens the definition of purpose that it is becoming almost meaningless. There must be some means of control, and if the control is exerted by other means, that means must be the author of the purpose involved.
Thus, there really is not simple answer to the question of what is the purpose of Life, except that there is no answer that is very useful in any sense of the word. In short, we could say there is no purpose to the question.