A function of a man is to think, and maybe that is the why we are here, on surface of this stone traveling though endless space.
It is no longer politically correct and appropriate to refer to humanity as man. Because that is archaic, exclusive, patriarchal and gender specific.
That whole "I think, therefore I exist" mantra, as proof of existence, is putting the cart before the horse though.
You start by thinking you exists anyway, that is why you start with I.
It is like saying "I exist and think, therefore I exist"
A tautology.
Also, how do you know that thinking and existence must coexist?
After all, we have good reason to think a lot of things exist without being able to think.
How do you know that it is impossible to think without existing as an "I" entity?
If we create some sophisticated software logic that is capable of thinking, through Artificial Intelligence for example, will it be justified to say "I think, therefore I exist"?
Will that software logic become a person with an "I" self identification?