I believe the first suicides were due to feeling like a burden because of old age or physical damage/disability. Like, there are a lot of disconnected myths about elderly traveling elsewhere to die. I recall watching japanese The Ballad of Narayama (1983) wiki about that this year, but I've heard folk stories and tales about such phenomenon since I was a slav child. I believe it started to happen when life of humans became more or less stable so majority of them started to predictably reach some age over their physical prime and their year-to-year survival became a stable routine rather than daily fight. So, wehw, they had ability to choose death, rather than it being choosen for them by their tribe or a lucky animal.

Nowadays though, we have a lot of additional constructs that inspire us to take our lives, like being born into the wrong place, race, family, material conditions, being ugly and unpopular, having no way to succeed in life playing by house rules. We have a lot of lines we can cross to end our social life or harden it too much, making it virtually or literally unsalvageable. Our ancestors could kill themselves by an animal or a high enough cliff when they felt they can't hold a spear, and in a sense, the system we built on top of us can artificially condition us to be able or unable to survive in the same way, but it is crushing that it rarely depends on our own willpower, but some preconditions out of our reach. If you don't have specific skills to network and learn, was born as a foreigner and also gay, you have no one to give you a hand - it's harder than get out and hunt a rabbit, or look for berries, these penalties would decide your whole life, and you'd need to work extra each day to compensate them.

Farmers can have bad and good years, they can change crops or figure out something to not die in winter. They fight with something real, something they can touch, and if they are resourceful enough, nothing is going to be lethal for them, they can get over it.

In contrast, multiple highscoolers in my city hanged themselves over the years because they failed their final exams, for from day one all they heard is that these grades define their whole future, from being wealthy and/or doing what you like to end up everyone's embarasment on subpar jobs until you die in a shoebox. The pressure, the importance of such made-up thing made isolated young people decide they failed at life never to recover, and so they did the thing. I'm never tired of referencing Kafka, and being speedily judged by a black box test system that you have no future ahead for no valid reason is, well, completely heart-cracking.

My answer is: suicide wasn't invented, but we found new reasons for it, and ways to systematically encourage that.