Description:
It's not what you expect from the title, unless you expect cynical detachment sprinkled with misanthropy.

On the Meaning of Life
If you were to ask a dog, a chimp, a beetle, a bird or any other member of the animal kingdom about the meaning or purpose of life, what would you get?

Nothing - none of them talk.

Let us therefore assume that none of them is able to entertain such abstract thought, and even if, they haven't mastered language to the extent of being able to convey their answer in a way we'd understand.

At the same time, on an instinctual level their answers as displayed by behaviour would probably be along lines of these:
Survival of the fittest, reproduction to preserve, adapt and evolve the species, keeping nature's equilibrium 

If you ask a human being that same question: answers range from 'I wouldn't even know how to begin describing the complete absence of a clue' to 'I couldn't care less - because once I am gone everything else can go to actual hell'. 
Maybe, someone even offers something in tune with what every other living organism does.
I am not saying that I ever heard anyone say these things out loud.
Based on what I have seen I don't think I need to - history speaks for itself.

Here's the thing though, as arguably the only species capable of conscious awareness, for both the instinctual aspect we share with any other being, as well as the correlation between cause and consequence of the impact of human existence, the combined lot of us, the human race as a whole, past and present, it appears, we're not only really shitty at doing something with that information, we in fact got so good at working against that presumably common instinct you'd be tempted to think we abandoned it altogether. 

If survival of the fittest was a priority - we'd long ago banned the expression "do as I say not as I do".
We ought to have come to learn that "leading by example" inspires people, and not "telling people what they should or shouldn't do".

If preservation and evolution of the species were a goal, we'd not spend so much effort working against each other, exploiting each other, fucking each other over.

If keeping nature's equilibrium was of only an ounce of importance to us, we'd long ago accepted that we have become the one dominating species that every other creature is forced to make room for - at a devastating price paid by their realm and race; and that a lot of complex terms and conditions apply to obtain a refund for that.
Back in the very old days humans made sacrificial offerings to all manner of higher power - in the hope of getting good fortune in exchange.
These days, asking for a sacrifice is answered by 'what do I get in return?'. 
Yes, part of it maybe that the word no longer means what it used to (like literally), but I am confident that's the most trivial part of the dilemma. 
It would appear that we've not so much retained but recovered the instinctual truth that sacrificing is weakening, especially as far as tangible results go.

If observation is anything to go by, I am inclined to say that the purpose of a human being's life is to contribute to the extinction of life in line with what one's personal believes and morals are (that is including doing one's utmost to hinder that process) with the bonus objective being, to perish before the world as you know it ends.

It can thus be argued that the human race is first species actively helping its self-fulfilling prophecy.
That is the gift of free will. And the burden of a savage.