Written by: Matthew Sabatine
The following post/article represents only the views of the author and not everyone at Common Issues.
I once heard that the human mind is like a theatre. That makes sense to me. We have evolving stories that we tell ourselves that help us orchestrate unity, purpose, meaning, self-enhancement, and contact with other humans.  You may often take for granted what you tell yourself, but it matters more than you realize. Your body listens and reacts consequently to the multi-voiced, dialogical process happening within.
Some have stated that this was made standard and instinctive in us as a safeguard against anything menacing. This is a very old mechanism from the days when we had to be on high alert in the wilderness at all times to escape any predator at a moment’s notice. In the modern world we are stuck with this pesky thing that appears to me as a fixed trait, inferring that certain predatory threats and maybe other selective pressures have suffused throughout our species’ evolutionary timeframe to necessitate this fixed trait. It manifests itself in our unwarranted ruminations, anxious thinking, obsessions, compulsions, self-shaming and blaming. The old brain is so powerful that it can easily convince us that our negative, self-censorious thoughts are the true reality and that the hopeful, optimistic thoughts we want to think are idealistic nonsense. 
But awareness of these negative stories allows us to realize there is an alternative, that we have the power to switch those negative stories off when they are disadvantageous to then chart a new course and destiny. We can undo the mental tricks that mislead us into maladaptive angst. 
Please don’t assume I am saying that stress and negative emotions are adversaries all the time. Reality truly is not often a bed of roses, and when threats occur you don’t want to be blithe about them.
Let’s look at how the human nervous system evolved over thousands upon thousands of years to meet the unyielding pressure to outfox predators while also fighting off threats to psychological and physiological equilibrium, such as the loss of food, water, or shelter. Your starving body has internal conflict and doubts about trying to reach for an apple on a tree while you are several feet away from a venomous snake helps to illustrate my point, I think. Your survival intelligence helps you to scan your complex environments and circumstances, and to grasp the array of options and several different outcomes that could result from what options you choose. 
Many images can pass through the theatre of your mind when you see the snake in the tree: 1) you could flee from the scene of imminent physical harm but then you would have to continue starving until your find another fruit-bearing tree 2) you could remain stationary in the midst of the snake to think about what to do next, although standing there and just thinking will eventually reach its pinnacle of usefulness, at which you would then realize something else needs to be done 3) lastly, there is the adapt by using a weapon to knock the snake down from the tree with a large stick, after which you will beat it. Luckily for you, you could have a machete to sever its head or a gun to shoot it. If the environment doesn’t favor you much, but your survival intelligence makes you resourceful and dexterous, you could invent an adequate weapon with the objects around you. The stronger the weapon, the more your chances increase for making successful adaptations and survival.
To adapt to the changing ecology around you, this is helped by your neurobiology and your phylogenetically old midbrain governing your reflexive fight-flight-freeze defenses.  They are tightly interlocked with and neutrally galvanized by, but also compete with, forebrain structures including the prefrontal cortex (PFC) and amygdala. You weren’t expecting to encounter a snake because you had not apprehended it ahead of time to instead seek another apple tree, so now you must efficiently outmaneuver this natural danger. The parts I mentioned would coordinate your fear response, assessment of potentials rewards, discernment of consequences, and making the appropriate behavioral choices that reach the upshot with the snake.  
Thanks to our Pleistocene forebears, who could employ great problem-solving acumen in fluctuating environments and novel circumstances, the modern human brain is now great at ad-libbing and has cells that can become attuned to coding whatever sights, sounds, smells, and tactile sensations are relevant to the current environment. 
Rodents may have been the frequently chosen test subjects in experiments for understanding threat responses, but it is reasonable to say that if rodents shared their environments with our forebears from long ago, then they must have endured very similar selection pressures and challenges. Certain sophisticated selective pressures that we think are only present today could have existed throughout our evolutionary history of human survival intelligence; these could have been “cunningness, an understanding of others’ sinister desires, and metacognitive processes including meta-strategic knowledge. Thus, higher-level and more integrated cognitive and computational systems embedded in our nervous system are likely to be critical to human survival.”   The brain’s supple and plastic character, made for superlatively handling an ever-changing world, is based on research about the adaptive information-coding cells’ specialization and enablement to carry out various roles, with these cells probably having their location in the prefrontal cortex. This was “research using non-human primate electrophysiology.”  
Looking at our evolutionary history and its influence on the human brain, it becomes a bit clearer as to why debilitating stress, anxiety and depression occur. These maladjusted, unstable mechanisms in you are trying to ensure several vital survival strategies are fulfilled: 1) That you can predict and prevent the threat in the pre-encounter stage, 2) That you can assess the threat in the post-encounter stage, 3) That you can react lickety-split as the threat is gaining proximity or in the midst of the attack. Furthermore, these strategies rely on a system that is keenly tweaking and fine-tuning your threat circuits based on “associative learning and higher-order inferences.” Unified cortical-hippocampal systems support your inner simulator of possible scenarios that run through your prefrontal cortex, amygdala, and the bed nucleus of the stria terminalis (BNST), which is a crossing point between the affective forebrain. 
We can’t be as quick, keen, cunning, and efficient as we are without our imagination systems using vivid and arresting images to see possible confrontations. We need these imagination systems to mitigate threats through reforming our environments, to establish social alliances, to empathize, to employ vicariousness, to use elaborate symbolism when ratiocinating with others, and to bring data together to build new knowledge about threats. 
It is the flaw of the human Survival Optimization System that we tirelessly reflect on the past, compulsively foresee troublesome futures, develop affective disorders, are oversensitive to social rejection, and fear leaving the safety of our protective familiar environments.
Apparently, we are hardwired to be sad and depressed, at least that is the interpretation that some have made. But is that true? I found a July 2019 article written by Rafael Euba from Scroll.in and its title is “It’s not you, it’s evolution: Humans are designed to be sad” which prefaced the idea that “happiness is a human construct, an abstract idea with no biological basis.” The crux of his logic is that we have a big frontal lobe, that is designated for analytical and executive functions, and had developed inside us instead of neural circuits and regions that could generate natural happiness. Depression’s non-elimination in human history has served the adaptive purpose of helping us unhitch ourselves from situations that are too doubtful and delicate to handle. Apparently, happiness is a pipedream sold to the American public by a billion-dollar propaganda industry. Happiness is discrete from the primary goal of survival and reproduction, because it disarms us against likely threats. 
In an 2014 article from Aeon, Jacob Burak states that “two-thirds of neurons in the amygdala are geared toward bad news, immediately responding and storing it in our long-term memory…” and “good news, by comparison, takes 12 whole seconds to travel from temporary to long-term memory.” 
Jackson MacKenzie’s book, titled Whole Again, which discusses healing yourself after abuse, also recognizes the human being’s penchant for negativity. On page 10, he states, “The mind (especially the ego) has a negative bias. It is scientifically proven to be wired that way to protect us, often activated after traumatic situations. However, we’re not running away from lions in jungles anymore, so that old wiring is really no longer helpful to us. We have these wonderful brains that can learn from mistakes and make future adjustments, without activating the old run-away-from-lion mode.” 
But before we conclude that we must spend the rest of our lives melancholically wasting away, perhaps we could accept his wisdom that negativity is the mind’s clever trick to get us to dismiss and disdain positivity. Meanwhile, happiness and freedom can be manufactured from “non-judgmentally” detecting these tricks and “un-identifying” with them. “Thoughts naturally become softer” once you achieve the “calm sensations replacing the tension and agitation in your body” that ensue from your disengagement with these mental tricks. We should use “unconditional love” as our “foundation”, because it is a source that never wants to leave us unnurtured, even when we falter and can’t feel it. This must be a love that doesn’t seek for others to fulfill our picturesque image of “romantic obsession, saving or rescuing, self-sacrifice, attention, and sympathy.” 
Apparently, the Dana Foundation disagrees with the notion that we are foredoomed with sadness. For them, happiness is not a mere cultural construct, totally discrete from any biological basis. A 2006 article cites the 1950s revolution that took place with Ph.D. holders, James Olds and Peter Milner, who observed the “pleasure centers of the brain” that were electrically stimulated in rats as they pressed levers at great speed. The nucleus accumbens was found to produce motivation, and for humans, activating the nucleus accumbens will prompt smiling, laughter, satisfaction, confidence, and increased well-being. When the cortex receives and systematically organizes sensory input that implies a reward, the ventral tegmental area (VTA) in the midbrain gets a signal and secretes dopamine into the nucleus accumbens, the septum, the amygdala, and the prefrontal cortex. 
I certainly don’t want people to unquestioningly obey the opulent happiness-salespeople, especially when we know which of their products don’t work. But we also don’t want to settle for negativity business’ messages that could plunge us into the wretched dumps of nihilism. There must be a healthy balance between the negative and the positive.
 MacKenzie, Jackson, Whole Again- Healing Your Heart and Rediscovering Your True Self After Toxic Relationships and Emotional Abuse, pg. 10-12, TarcherPerigee (January 8, 2019), Print.