It wasn't long after I came to believe the Church wasn't true, that I came to believe that in all likelihood, there isn't a god either. The cosmos then lacked the ability to give purpose or meaning. It did not create all that existed for a reason nor with intent. Creation came about by mindless matter/energy simply carrying out the soulless laws of nature.
At first blush, that makes the universe a rather emotionally cold and scary place because no powerful essence is looking out for you. You face the raw elements alone and if something tragic happens no Thing will notice, care, or rescue. The awareness of this and bold confrontation of this is what constitutes existential angst. Many people are so uncomfortable with the thought, that they will not allow their minds to accept or even entertain it. "There must be universal meaning," they protest with nothing to support their declaration other than their own discomfort.
But, why this discomfort? Why this angst? Must it have come from a god; a creator to persuade us He is there? If not, then why or how did nature put it there through evolution? Why does it seem that most animals and young human children never have to confront this angst? Why is it only the burden of adult homo sapiens? Why can't why be as blissfully unaware or unconcerned with the meaning of life? Maybe we need to become unconcerned with it and simply live as others do.
Is this dissatisfaction with meaning a mere side effect of other mental abilities which gave our ancestors an evolutionary advantage? I think so. One of our great abilities is to problem solve. When we solve problems trace back the steps to determine cause and effect of how the problem situation happened. Then as we attempt to come up with solutions, we play out in our minds how what we do might start a chain reaction to our desired end result according to what we know about how things work. We sense a disparity between what is and what we want. Then we give purpose to actions we take and tools we use. Their purpose is to make contributions to help us reach our desired goal. For example, we give a twig purpose when we use it as a tool to get to the termites in a stump. The twig has meaning for us as a termite getting tool.
I believe we humans began to see all things around us as potential tools to help us reach our desired ends. Even other people began to have meaning in our lives when we saw that they could help us get what we want. And then thanks to an ability that does not fully mature until our teen years, we are able to reflect on our selves and see ourselves as objects in the world. Once we can do that, we begin to wonder what purpose we serve and to whom are we a tool. That leads us to the next question, is all of creation a tool in the eyes of a being that could manipulate us all.
Now, organisms have a desire to conserve energy. It gives us an evolutionary advantage as it traditionally took a lot of calories to catch and consume calories, so it is best if you hold onto your calories until you need them to gather additional calories. So, we are lazy. If there is not a purpose behind an action (i.e., shelter, food, sex, etc), then our bodies slow us down and demotivate us. One why our bodies get us to slow down and be demotivated is through depression. When depressed our bodies are telling us whatever we are doing is not working, slow down, think it through, and come up with a better approach or regoal, but you have been wasting energy going down that path. We have learned to look for a purpose for doing something before you do it. If we can't find a purpose, we say, "What's the point?" and then don't bother.
So, let's put it all together. We aquired the ability through evolution to give meaning and purpose to things. We also aquired the ability to see ourselves as objects and wonder whether someone or something might have meaning or purpose for us. We need a reason to act, or else we want to conserve energy. Although we can see the functional reasons were do many survival tasks, we may start to wonder whether survival itself is worth the effort. What's the point?
(I have run out of time to finish. I'll post more later.)