(These are just my thoughts, not an official representation of any authority on the matter. Some of the terms presented here use my own idiosyncratic definitions and may have different meanings elsewhere. It's also not at all a comprehensive view on the topic but only a rough summary based on my limited understanding.)
 
I've spent the past year or so really trying to wrap my head around the essence of Tier 2 cognition (starting at Yellow), namely systems thinking. Just these past 6 months, after taking some courses in communication theory and community psychology, I've gotten some insights into the matter that really solidified my previous intuitions which I'd like to share here. I was truly surprised of how much these two fields were based on systems theory (mainly the theories of Gregory Bateson and Urie Bronfenbrenner respectively, although these two theorists only serve as lightning rods for the vast meta-theoretical space that is systems thinking).

I'll open up with a quote from each of the aforementioned theorists:

What these quotes have in common is that they emphasize relationships or interconnections. That is what a system is: a collection of relationships. But isn't it the case that anybody can understand concepts such as "relationships", "interconnections" and "systems"? What makes systems thinking so special? Now, you could actually argue that systems thinking itself isn't necessarily confined to Tier 2. However, I'll say that Tier 2 cognition consists of something called a "mature systems view." It's about a way to view the world; a worldview, and it's of a certain sophistication or maturity. To truly understand this worldview, we must first contrast it with a more common worldview, which I will call "analytical thinking."
 
Analytical thinking

Fritjof Capra, a pillar of the mature systems view, refers to this worldview and way of thinking as the "Cartesian-Newtonian paradigm." It's characterized by reductionism, mechanism, atomism and positivism. The Cartesian method approaches understanding the world by breaking it down into smaller components (reductionism). Newtonian mechanics describes the world as force interactions between physical objects that consist of atoms (mechanism, atomism). Positivism refers to the idea that we can formulate consistent laws based on this type of knowledge (e.g. "laws of physics").

Another way to think about it is that analytical thinking approaches the world "vertically":


This vertical approach isn't just confined to the hard sciences (physics, chemistry, biology). It's also central to fields like psychology. The analytical tradition of psychology reduces problems down to components within the individual: symptoms, diagnoses, traits, drives, genes, beliefs, values etc. It lays the basis for individual psychotherapy (psychoanalysis, Cognitive Behavioral Therapy etc.), psychiatric medical treatment (antidepressants, anxiolytics etc.), personality psychology (Big 5, MBTI etc.), cognitive psychology (e.g. Beck's schema theory) etc. Jordan Peterson is a big proponent of this view.

On the other hand, there is a systemic tradition within psychology called community psychology. It emphasizes relationships, connections and environmental factors when solving problems (social, economic, political, cultural etc.). Not coincidentally, Jordan Peterson is not a big fan of this approach. Without making this any more about our beloved JP, let's get straight to it: what is systems thinking?
 
Systems thinking

In contrast to reductionism, mechanism, atomism and positivism, systems thinking is relational, holistic, ecological and organic. 

A system is a collection of relationships between units, and holism is about focusing on the whole. Taking a systems view is about seeing the interplay as a whole, not just the individual units for themselves. The bigger the system view, the greater and more inclusive the whole becomes, and the more holistic it becomes. Ecology is about understanding the relationships between organisms and their environment, and an organism is an interplay of smaller living units ("organs" or organic units). Systems in nature and society are complex and can be described using different concepts from systems theory (e.g. "transaction", "self-organization", "adaptation", "feedback" etc.).

In contrast to the vertical nature of analytical thinking, systems thinking is "horizontal":

 
This picture represents a social system, however the horizontal principle applies to other systems as well: organ systems, cells, molecules, atoms etc.). These are «real systems» (natural/social systems). You also have abstract systems (e.g. scientific theories, ideologies, value systems, meta-systems, paradigms, meta-theories etc.), and that's where things like construct awareness come into play (more on that later).

Meta-theories are "theories about theories", which try to understand how abstract systems work through meta-systematic observations. Fields like philosophy of science and models like Spiral Dynamics and Integral theory are examples of such meta-theories. Model of hierarchical complexity (MHC) is a good model to understand the different levels of abstract systems (e.g. "how complex is a paradigm?").
 
Context awareness, Construct awareness and Theory pluralism.
I've already mentioned construct awareness, which is one of three main facets that I think are useful to further understand systems thinking:

 
Context awareness refers to the general ability to understand the pervasive nature of relationships in the world: the vast array of relationships across different domains (physical, biological, social etc.). Any individual unit exists within a larger context (their environment or the larger system), and being aware of context is synonymous with a general form of system awareness.

Bronfenbrenner's Ecological systems theory is a good illustration of context awareness:

 
Construct awareness is the ability to the understand the relationship between the human and the world with respect to making sense of the world (knowledge, sensemaking and epistemology) and how it's a process of constructing abstract systems. People may manipulate these abstract systems without understanding how they work, e.g. what kind of system it is, how it's made, and how it relates to other systems, which would be an exercise in construct blindness. For example, it's possible to operate a car without knowing how it was made or how the engine works. To not be aware of how abstract systems work to construct your reality is to have a lack of construct awareness.

Thomas Kuhn and his book "The Structure of Scientific Revolutions" is a good example of construct awareness. After performing a meta-theoretical study on the historical development of science, he concluded that all scientific theories at all times are validated relative to a historically contingent framework of philosophical assumptions (a paradigm, a collection of constructs), and thus all scientific knowledge is fundamentally relational in nature. So not only are the external aspects of human behavior dependent on context (as in social interactions; Bronfenbrenner), but also the internal aspects (mind). If we go back to Gregory Bateson, in his systemic communication theory, he in fact defines "context" not as something external, but as an internal psychological framework. He does this because of the insight that the mind is constructing the external world. Alfred Korzybski's "the map is not the territory" is also a staple of construct awareness.
 
With enough context and construct awareness, you'll inevitably end up with theory pluralism: the ability to explore and understand a wide range of different abstract systems (theoretical frameworks). In a sense, theory pluralism is both a prerequisite and a consequence of construct awareness (they're co-created). However, to really develop a wide knowledge of theory, you must have a deep meta-theoretical understanding which is able to see the larger picture – the essence of construct awareness. Ken Wilber is a great ambassador for theory pluralism. His vision of integrating all domains of knowledge into a single, comprehensive framework is the pinnacle of systems thinking. Fritjof Capra should also be mentioned here with his book "the Tao of Physics", where he not only makes profound observations about context and construct in his writings about Quantum Mechanics, but he also makes theoretical comparisons to Taoism and non-duality.
 
I mentioned earlier regarding having a "mature systems view" that systems thinking is not necessarily confined to Tier 2 cognition. This is because Green is very open to context awareness and will easily appreciate models like Bronfenbrenner's ecological systems theory. What Green struggles with the most is construct awareness. It might be able to deconstruct a lot of Orange systems, both from a rational place and an intuitive place, but it struggles to pick up the pieces, both theoretically and practically. Construct awareness also makes you more prone to grasping the concepts in systems theory, which unlocks key concepts like the meta-theoretical evolutionary lens (Beck & Cowan, Wilber, Kuhn), which Green crucially lacks.
 
So that is the gist of it, but there is so much more I could talk about, e.g. the history of systems theory (deep ecology, cybernetics, Gestalt psychology etc.) and different systems theory concepts like I've alluded to earlier. There are also other aspects of Tier 2 cognition that could be expanded upon, like the ability to hold paradox, understanding holarchies, or different real-life applications (that's a big one). I would anyways like to hear what you guys have discovered about systems thinking that I've left out. I would never turn down the opportunity to deepen my theory pluralism  
 
 
 
 
 
 
 
 
 
 
 
 
Additional notes and clarifications:
Expanding on this:
 
Analytical thinking and systems thinking must not be thought of as diametrical opposites, but as generally expressing different dimensions of movement through abstract systems (vertical vs. horizontal). Neither of them are pure expressions of either "vertical" or "horizontal" thinking, because technically all abstract thought utilizes both dimensions to navigate the cognitive landscape. An alternative description could be hierarchical movement vs. cross-hierarchical movement. The categories explored in hierarchical movement tend to have a corresponding familiarity or similarity of kind, while the ones in cross-hierarchical movement have corresponding distance or diversity of kind (in that it's possible to have many qualitatively very different things interacting with each other in a system).
 
One reason why horizontal movement tends to be more readily associated with complexity might be due to the relative simplicity of postulating it abstractly, because meanwhile it's possible to have interactions between many qualitatively different things, it doesn't actually necessitate or force a qualitative difference (e.g. you can simply have interactions between many molecules of the same kind), meanwhile a comparably complex vertical scenario is much harder to postulate, as the different levels of a hierarchy always forces a degree of difference (e.g. molecule > atom > sub-atomic), and thus most abstract hierarchies tend to be simpler (because models are supposed to simplify). In other words, the tendency towards horizontal complexity could simply be a bias of abstraction, and that in reality, systems are equally infinitely complex across all dimensions, both vertically and horizontally. Thinking is nevertheless about abstraction, and therefore horizontal thinking serves as a litmus test for complex thinking.
 
So from this alternative view, what is systems thinking? Well, the more you refine your general ability to abstract both vertically and horizontally across categories (symbols, concepts, classes and domains), the more expansive and complex your thinking becomes. Therefore, the proclivity towards the mature systems view simply depends on the size and complexity of one's perspective. Horizontal thinking is nevertheless generally an indicator of complex thinking.

I see this misconception way too often (conflating dependence and addiction). You have dependence, which can be either physical or psychological in nature, and you have addiction, which is psychological in nature.
Dependence is simply a range of symptoms that occur as result of withdrawing from a drug, either from coming down from a single drug experience or from discontinuing frequent use or abuse. The physical symptoms relate to vital physiological functions and can be life threatening, while the psychological ones relate to physiological feelings like low mood and dysphoria.
Being drug dependent simply means that your body, in order to maintain optimal functioning, has tuned its adaptation mechanisms to accommodate the drug-mediated change in activity, which involves decreasing the activity that the drug is elevating (downregulation). Roughly speaking, dependence happens on the level of receptors. For example with cannabis, it happens at the level of CB1 receptors.
On the other hand, the mechanism associated with addiction is what initiates drug-taking behavior, produces drug cravings, and is for all intents and purposes psychological in nature. Addiction operates technically adjacent to drug-specific receptor activity and more on the level of networks (specific dopaminergic pathways). In other words, it doesn't really matter whether or not you feel dysphoria from drug withdrawal (e.g. low CB1 activity): if you're addicted, it's possible to feel drug cravings despite having been off drugs for a while and having stabilized your drug-related systems (normalized CB1 activity).
So when people say "weed isn't that bad, you can only get psychologically addicted", it's firstly a conflation of dependence and addiction, and secondly it's a misunderstanding of the mechanisms that lead to compulsive drug-taking. While it's true that cannabis doesn't produce physical dependence at the same level as say heroin, it's not the dependence aspect that technically initiates the compulsive drug-taking behavior in the first place. The conceptualization of physical dependence should not be one of "intense, dangerous cravings" but rather "the presence of usually innocuous but potentially life-threatening physical symptoms, ranging from a light cold to intense, seizure-inducing over-activation".
An useful analogy is how a diabetic is dependent on exogenous insulin to survive. The diabetic doesn't feel cravings because of the lack of insulin (he isn't "addicted"), but his body is dependent on insulin for optimal functioning. That is what heroin is to a heroin dependent person. Now, meanwhile it's certainly true that a heroin dependent person is also probably plagued with addiction, it's not actually the physical symptoms that makes you take the drug. A way to make this abundantly clear is to consider the fact that cocaine is not considered to produce physical dependence ("wow?").
Although it's certainly the case that dependence and addiction interact to produce what is normally associated with compulsive drug-taking behavior, the two are to be treated as separate concepts, and it's the activity in dopaminergic pathways that initiates the motivation, movement and reward-seeking behavior that leads to drug-taking behavior, not the downregulation of drug-specific receptors. Repeated administration of such dopamine-elevating drug will strengthen these pathways, increase cravings and reward-seeking behavior, and potentially lead to addiction. This is what is mean by a reinforcing drug (strengthening reward-seeking activity).
So to take this back to cannabis, it's perfectly possible to become addicted to cannabis as it increases dopaminergic activity in major reward circuitry in the brain. Being addicted to cannabis is not the same as being dependent on cannabis (although they certainly correlate). Addiction is a mental phenomena, but this does not detract from its seriousness. Addiction to cannabis, alcohol, cocaine, heroin are all mental phenomenas.

Thank you ?
 
The understanding of the lower levels is required in order to perform the operations in the lower levels, so in this sense, the higher tasks always involve the lower tasks, but maybe more in an implicit way rather than explicitly. The hierarchical structure means that you can start at a higher operation and trace it all the way down to the first level. I'll try: 
Cross-paradigmatic (14) : Crossing two different paradigms (e.g. evolution and economics) means seeing how they interact, e.g. the competition between market strategies fulfilling the conditions for adaptive evolution.
Paradigmatic (13): To see how they interact, you must have a basic understanding of both paradigms (evolution and economics). That means you need to have an understanding of specific aspects of each paradigm (or the relationships between different metasystems): e.g. in evolution, you have the relationship between reproduction and different selection mechanisms; or in economics, you have the relationship between scarcity and supply and demand.
Metasystematic (12): There are different systems under each of those. For example, for reproduction and selection, you have assortative mating and directional selection respectively (let's stick to evolutionary theory for now).
Systematic (11): Examples of systems within those metasystems could be inbreeding and splitting selection respectively.
Formal (10): To understand these systems, you have to commensurate synthetical statements (empirical observations) and analytical statements (logical facts), formulate hypotheses and make logical deductions, a.k.a the scientific method (or "the hypothetico-deductive method"). Let's take inbreeding as an example: "if individuals in a population with a shared ancestry mate with each other, they're practicing inbreeding. Me and my cousin are related and are mating, therefore we're practicing inbreeding".
Abstract (9): To perform these operations, you must be able to form variables and quantify propositions, e.g. analytical statements ("inbreeding is when individuals in a population with a shared ancestry mate"), or synthetical statements ("me and my cousin are related and are mating.")
Concrete (8): That requires the ability to understand complex interactions, plans, deals e.g. "me and my cousin mate every sunday, because that seems like a good time with respect to our responsibilities".
Primary (7): This requires an understanding of times, places, actions, e.g. "me and my cousin mate every sunday, because that is when our parents are gone".
Preoperational (6): This implies "when, then, why etc.". e.g. "me and my cousin mate every sunday, because it's fun".
Sentential (5): "me and my cousin mate every sunday".
I think I've made my point

00:00-1:07 This is what the transition from systematic to metasystematic looks like – going from seeing one system to many systems:
The step from systematic to metasystematic is in this case the departure from perceiving everything through one model (Newtonian mechanics) to getting familiar with many models (langangian mechanics, QM etc.), and then going from saying "this is the truth" (systematic), to "this system is right, all the others are wrong" (low metasystematic) to "they're all just different interpretative frameworks" (high metasystematic). High metasystematic is the advent of so-called relativistic thought ("so-called" because it's just what our modernistic or formal-systematic stage 10-11 culture calls it). It's relatively relative (more relative by contrast). In reality, there are different degrees of relativity all throughout the hierarchy which gets increasingly complex as you scale the stages.
Now, the statement "they are all just different interpretative frameworks" is one level of construct awareness. A higher level is when you recognize how these frameworks interact, and that is where systemic models like MHC come in. MHC lets you see the systematic structure of the relationships between metasystems and how they form higher structures (here refered to as "paradigms"). One such structure is the nested holarchy structure, or the spiraling motions of "trancend&include" (Wilber). Here you can see that the structure of different cognitive operations reflect an underlying metaphysical structure of all frameworks (here we use the external dimension of the Integral Quadrant as an example):
atoms include but transcend sub-atomic particles;
molecules include and transcend atoms;
proteins, sugars and lipids include and transcend molecules;
cells include and transcend proteins, sugars and lipids;
organs include and transcend cells;
organisms include and transcend organs;
groups include and transcend organisms;
societies include and transcend groups;
civilizations include and transcend societies;
planets include and transcend civilizations;
solar systems include and transcend planets;
galaxies transcend and include solar systems;
galaxy clusters include and transcend galaxies etc.
This is what is meant by "the fractal nature of reality". This is also why Integral Theory is so genius because it goes meta on so many aspects of all frameworks. "Levels" is the so-called "vertical development" (stages of development in SD, MHC; all stage models) that follows a pattern of nested holarchy. Quadrants are different domains of frameworks (individual-collective x internal-external) that also follows a pattern of nested holarchy. Together, it creates AQAL (All Quadrants, All Levels): 

If you do something that is not beneficial for survival, your body will tell you by sending some signals. If you keep eating cake after you've had enough cake, your body will tell you by making it taste bad. If you touch a hot stove, it will feel bad. If you don't eat food when you're hungry, it will feel bad. To maximize pleasure, you must do the right things at the right time.
Your body as a self-perpetuating life system needs to maintain a steady internal state (homeostasis) in order to survive. Survival means to keep a fixed boundary between yourself and the environment, and complex creatures like humans have evolved elaborate behaviors to aid in this process (avoiding predators, routine feeding behaviors, seeking shelter etc.) along with more basic physiological processes (maintaining a constant body temperature, acidity, water content etc.). 
The nervous system is one of many systems that work to control such behavior and maintain homeostasis by using signalling molecules like dopamine. Dopamine is involved in things like movement, motivation and seeking rewarding stimuli, but pleasure only happens once you do the work that dopamine tells you to do, and when the work is over, systems like the serotonin and opioid system take over (movement stops, you rest, sleep etc.).
You seek what is pleasurable because it aids in your survival, and things that give you pleasure generally do aid in your survival. If you go against your own survival and homeostasis, your signalling systems will tell you this, and hedonic adaptation is one such process, i.e. feeling less pleasure from eating more cake after you're full, or drinking more water after quenching your thirst, or having sex for the 12th time in a day. There is a myriad of different adaptation mechanisms in your body that all work together to make your life possible  
The need for success and achievement is a higher-order expression of deeply rooted survival drives, and they follow the same adaptation mechanisms and use the same signalling systems as the lower ones. For example, the movement through a social hierarchy is tracked by serotonin levels. Your motivation to finish a project is driven by dopamine etc. Your signalling systems also generally respond to changes in stimuli. If you sit on your butt for a while, the feeling of pressure that you experience while initially sitting down slowly disappears. When a stimulus becomes persistent and static, you adapt to it by decreasing the receptiveness (unless there is a positive feedback loop that increases it, like with certain pain pathways).
This tendency to respond to change is what drives people to constantly seek new stimuli and explore new environments. It's why millionaires keep earning more money even though they have all the money in the world. It's why the biggest bodybuilders think they look small in the mirror. Experiencing change is also a source of strength and health as it challenges your system in new ways, engages a fuller range of capacities and resources, and perks your senses. Experiencing stagnation makes you numb, depressed and nihilistic. In many ways it's the voluntary confrontation with change that creates desire, drive, meaning and not least pleasure.

This is meant mostly for young seekers who are juggling early life with self-transcendence.
 
 
It's no surprise that the most awakened people you see in the world are some of the most well-integrated and resourceful people out there. While it's not uncommon for mystics to enter a deep introspective phase of their life, it's not an unproblematic endeavour. In the past, being a mystic was synonymous homelessness, and fortunately for them, there were structures in place that made it possible to survive (Indian culture is very accommodating to mystics). However, in the modern world of Western individualism, it's not a wise decision to leave your life behind, certainly not before it has even started.
I recommend re-defining the concept of spirituality from the idea of seeking the highest to integrating the whole. What makes us human is our desire to expand endlessly, and the ultimate expression of this is the desire for truth. You can imagine the desire of truth to be an expansion towards the highest altitude of consciousness. However, the impulse of expansion does not only extend towards higher altitudes but also towards wider breadths and deeper depths. It's not just an movement upwards, but rather it's an expansion in all directions.
So in other words, to be truly spiritual is to maximize all expansion in all aspects, not just the higher ones. In fact, when the lower aspects are denied their right to expand, they will impede your ability to go higher. For example, if you deny your sexual energy, this will create a disruption in your emotional system and impede your spiritual energy. There are a myriad of "lower energies" within you that need to be processed and expressed before you can fully move on to the next level (e.g. the desire for safety, belonging and esteem), and working on the wordly things will help you in that direction.
So it's not just that it's impractical from a survival perspective to not develop the lower aspects of yourself, but it will also cause problems for your truth-seeking. I can use an example from my personal life to illustrate this point: I've personally had a little "wood mystic" phase in my early teens (dropped LSD a couple of times, started smoking weed heavily to expand on those insights). What initially began as an intense seeking for truth turned into a denial of personal responsibilities and avoiding the hardships of life (stopped caring much about school, friends and family), and the stress from having to deal with all those bad decisions made me very neurotic and depressed.
I later realized that the dysfunctional part of my behavior stemmed from some emotional issues, namely having had very strict parents that didn't let me fully express my emotional impulses, and that me immersing myself completely in truth-seeking and avoiding responsibilities was me trying to fill that hole from my youth. Something as basic as the need to express one's impulses (to consume, to indulge, to "want", to self-assert), which I expressed through intense truth-seeking, was ultimately creating more problems for me and holding me back.
What I was avoiding, and what I'm focusing on now, is to integrate my personality, harvest my potential, become a resourceful person and then go directly for truth without being a liability to others. I'm not saying that what happened to me will happen to you, but there are many things that can go wrong if you take the seeking approach over the integrating approach. Every part of your life impacts every other part in some way, and if you fail to address one part, it will have a detrimental impact on the whole. This is essentially a lesson in holistic thinking: of not getting too caught up in one aspect of life, but to be able to see the bigger picture.

I believe I also got some insight into what the ingredients are that go into creating a clinically psychotic mind (a mind that looses its ability to keep in touch with a relative, socioculturally sanctioned consensus reality), because to be totally honest, I had some glimpses of that within myself, and I was probably going down that road if it wasn't for a sequence of very fortunate events.
In short, I believe that the psychotic mind is just the end result of spiralling down that dysfunctional feedback loop: unresolved trauma, paired with a hyperactive mind and a neurotic personality (negative internal attribution style, introversion, excessive rumination, anxious attachment style etc.), excacerbated by external stressors (substances, life events), and an escape into an idiosyncratic and mentally constructed world. The mind reacts to the aforementioned conditions by dissociating itself from the "normal" types of cognitive patterns that otherwise ground you in an emotionally embodied and socially aware consciousness of reciprocal collective understanding, and instead ventures into an abstract and vaguely defined mentalscape with loosely defined concepts and arbitrary semantic connections.
They say it's hard to distinguish genius from madness. I say that madness is when the hyperconnectivity and isolation of one's semantic content exceeds its sociocultural bearing capacity; that one corrupts one's ability to mediate between one's own semantic structures and the common semantic structures held by other people in the local environment, and this usually happens like I said in a runaway chain reaction that eventually terminates in a psychotic break. In milder cases, it goes by names like magical thinking or thought disorder. Now, what is so genius about the genius is that instead of retreating into his own fantasy world, he holds consensus reality in one hand and the hyper-creative, non-linear mental space in the other, and the result is a beautiful synthesis – a bridging of the two worlds – which is able to inspire and innovate.

The relative is dual. The Absolute is non-dual.
Duality is comprised of two parts that make up a whole (e.g. hot-cold, up-down, big-small).
From the relative perspective, duality is two. From The Absolute perspective, duality is one.
From the relative perspective, you can choose between many different purposes. From The Absolute perspective, there is only one purpose, which also means there is no purpose.

1. If the universe is finite (not infinite), there must be a border that limits and contains the universe:
( U )
 
2. However, if we assume that the universe contains everything that exists, it must also contain that which exists on the other side of that border:
U( U )U
 
3. If you say that there doesn't exist anything on the other side of that border, then that other side is not limited by any border, and therefore that other side must be infinite, because there is nothing that limits it:
...UUU( U )UUU...
 
4. If instead any other side of any border is always limited by another border, there has to be an infinite amount of borders:
...(U(U(U( U )U)U)U)...
 
5. Therefore, the universe has to be infinite either way, with or without borders, because the universe is all of it:
U = ( U ) + U( U )U + ...UUU( U )UUU... + ...(U(U(U( U )U)U)U)...
 
In reality, the border is only something you draw in your mind. There are no borders in reality. There is only U

Yes, they have less psychological suffering, more peace, presence, less mental anguish, but they are not enlightened. As far as we know, they don't have awakenings, their state doesn't change, and there is no spiritual progression. Maybe this will be studied in the future and we'll have maps for animal spirituality as well. However, our current maps of enlightenment are limited to humans, and I haven't heard of anyone who was born enlightened.
Even if it was technically possible to be born enlightened, it would just be too extremely rare to matter to anyone. There are always exceptions to a rule, but the utility of the rule isn't defined by its exceptions. I think the progression component is a pretty useful way of defining enlightenment. The very reason why it's such a hot issue in the first place is because it's a sought-after thing that very few people have accomplished. In that sense, enlightenment isn't as much of a quality as an activity.
However, you can also make qualitative definitions of enlightenment that would still exclude animals, namely the idea that it's synonymous with what I like to call "non-dual baseline awareness", where "non-dual baseline" is defined by a lack of self-referential thoughts ~95% of the time (5% attributable to hypoglycemia). Now, the crucial point is that what I just mentioned only applies to humans. I will explain why that is:
Firstly, the concept of "baseline" implies that the potential for self-referential thoughts is always there (the underlying mental faculties never disappeared), and sometimes they may even reappear from time to time. Secondly, many self-proclaimed enlightened humans (who I believe to fall under the aforementioned criteria) still claim to be able to deploy thought as a means to an end ("non-self-referential thought").
In other words, enlightenment in this case would be "non-dual baseline awareness" + "the ability to think in order to plan or solve problems". So for an animal to be enlightened in this case, they would need to 1. have no self-referential thoughts and 2. have an ability to think (which isn't so clear). If you instead say that they're just innately unable to form any thoughts at all, that would distinguish them from all other "formally recognized" enlightened beings.
Then you have special cases where some enlightened people claim to have lost all forms of thought all together. Now, does that make them an animal? Well, even if they lack the subjective experience of solving problems using mental representations (through visual imagery or internalized verbal reasoning), they still display the same abilities as someone who does that. In other words, they can still pass as someone who is able to think to solve problems. Then the definition becomes more or less tautological in respect to the question: no self-referential thoughts + display of human behavior, i.e. only humans can be enlightened 
In summary, it's most useful in my opinion to define enlightenment or an enlightened being as "a selfless, thinking being" (or atleast one that displays the behavior of such a being), the qualities of which is partially accessible on a continuum facilitated by spiritual practice, eventually reaching a maximum and stabilizing around a baseline.
I also want to make it clear that I've been mostly referring to the most basic type of enlightenment in various maps ("600s" — Ramaji; "Valley of unity" — Sufism; "the Absolute within the Relative" — Five Ranks of Tozan; "Sixth Zen Bull" — 10 Zen Ox herding pictures; "4th Stage" — Patanjali' Yoga Sutras; "4th stage" (Sattvapati) — Advaita Vedanta. https://www.realizedbygrace.org/levels-of-consciousness?lightbox=dataItem-jlvwww23. However, the no-thought state mentioned in the 6th paragraph is usually considered a much later stage depending on the map.

A big reason why many people doubt the existence of psychic powers is due to the fact that you can earn one million dollars if you're able to demonstrate it under a set of experimental conditions (James Randi's challenge) and so far nobody has been able to complete it. Is this really a good reason to say that psychic powers don't exist? Now, what I'm going to claim is that you don't have to go outside the paradigm of conventional scientific methodology in order to understand why this doesn't necessarily have to be the case.
When it comes to observing behavior in a scientific context, there is a distinction between observing a phenomena in its organic environment and observing it in an experimental situation. This is a huge methodological issue in fields like social psychology. In the experimental approach, you create an artificial environment where you can isolate different causal factors, but you can never be sure if you've demonstrated a causal relationship outside of that artificial environment. This is especially true when you're dealing with complex things like mental phenomenas and social dynamics.
There are many reasons to believe that the functioning of subtle behaviors like psychic powers are highly sensitive to specific conditions, both in the external environment and within the psychic's own mind. It's a well-established fact that once you put a person in an experimental setting, you're impacting the normal functioning of that person. Therefore, the inverse of the statement in the previous paragraph is also true: just because you can't demonstrate a causal relationship in an experimental environment does not mean it cannot exist outside of that environment.
If you're still in doubt, you can also venture a bit outside the realm of conventional thought and more into the spiritual realm (this is also just based on my opinion). I think that psychic powers work similarily to how more normal intuitional insights seem to work, in the sense that from the perspective of the person having them, it doesn't feel like "you" created the intuition, but rather that it simply "came to you". It's like this piece of information you were given is not really just about you specifically, but that it's a part of something greater than yourself. You can also describe this as a plan, a natural unfolding, the creative evolutionary impulse of the universe, or God. From this perspective, trying to prove the existence of psychic powers in an experiment for you to win a million dollars seems rather silly. Why should the universe care about you doing that? In what way is that a part of the plan? 
I also think that once your intention is to further your own survival through these lower motivational forces (recognition, fame, greed), this naturally closes you off to these higher intuitional domains. When you're operating from these lower aspects, you're messing with your connection to the greater flow of the universe. Just imagine the difference between a mind that is at ease with itself and a mind that is fuelled by egoic desire. These more subtle aspects aren't allowed to bubble up if your mind is constantly filled with all this noise from impulsive thoughts, desires and fears.
Let me know what you think. I would appreciate if you could primarily talk about your personal experiences rather than some belief you have. Have you ever experienced psychic powers or any subtle intuitional experiences? Please share

I had an insight when reading about memory consolidation and PTSD treatment methods, and how it relates to the progression of one's meditation ability and the decrease in self-referential thoughts.
It has been established that memories exist in a fragile state during recall in a process called "reconsolidation", which means that memories that are being recalled are always prone to being changed or even erased. This has been used to treat people with PTSD by giving them a drug that blocks the stress response (not MDMA in this case, but the mechanism is much the same) and having them recall their traumatic experience. When they recall their memory without experiencing the stressful emotional component, the memory will be reconsolidated in this new emotional context, effectively changing it, which has been shown to reduce the severity of their flashbacks.
Now, what does this have to do with meditation? Well, I've meditated for probably 1000 hours and I've been able to notice a progression over time and how it unfolds. What I'm claiming is that the process of recycling thoughts in meditation is similar to the stress-blocking drug treatment for PTSD. This is because you're essentially doing a technique that induces a calm state while continuously experiencing the same thoughts over and over and eventually changing the emotional relationship to each thought.
"But meditation doesn't make me calm at all?". Well, naturally the source of calm goes hand-in-hand with low self-referential thoughts (psychological calm), but even if the number of thoughts were to stay the same, the technique is also inherently calming on a physiological level (be it focusing on the breath, releasing bodily tensions etc.). The technique usually works to decrease thoughts in the moment, but the question is how exactly does it do this more successfully over time? More specifically, are there any potential mechanistic explanations other than the simplistic "practice makes perfect"? This is my claim.
How exactly does it work? Well, when you're in this calm state, you will have some thoughts entering your mind (obviously). These thoughts are synonymous with a spontaneous recall of a certain memory, and this memory will have to be reconsolidated in this calmer setting. Even if you feel like you don't have a calm mind, your thoughts will always be accompanied by an underlying sense of physiological calm, and the accompanying emotion will therefore be dampened or recontextualized to at least a tiny degree. It might not be true in every moment, but on average, this effect will make itself prominent and starts having an impact over time. 
When you do this consistently (over days, weeks, months and years), you can start to see how this can radically change how your mind processes memories, thoughts, emotions etc. What also happens as the thoughts start to feel less threatening, you'll be more able to grapple with the actual problems behind why they even feel threatening in the first place, and eventually the thoughts will have no reason to come back. This "fixing" aspect is in many ways completely automatic (sometimes the excess emotional load is the only problem), but it might also involve taking actions in the external world or just seeing things from a new perspective.
For sure, the thoughts themselves can still cause you to feel a certain way, but as your practice deepens, you'll attain the ability to simply witness the thoughts without reacting to them the same way, and the reconsolidation effect will at this point start to increase exponentially. You'll notice how being mentally calm, clear and present are all synonymous with eachother, and how a silent mind and a healthy body are two sides of the same coin.
This I believe is at least one mechanism behind how self-referential thoughts seem to decrease as you keep meditating (or at least one way to conceptualize it). Meditation is essentially a type of long-format self-therapy. This can also serve as motivation for people who feel they're struggling with an unruly mind and believe they're not seeing any results. According to this theory, just the mere action of consistently putting yourself in a state free of mental distractions, that is just marginally calmer compared to your normal state, will slowly but surely give you the upper hand given consistent daily practice.

I'm also taking a course in philosophy as we speak, and I think it's fascinating to read about how Christianity evolved from the very beginning and its ties to Platonism, Aristotle etc.. Something I find very interesting is how St. Augustin (354-430) introduced the concept of "faith", which is essentially how they started separating God from human experience (traditional monotheism).
St. Thomas Aquinas (1225-1274) made the distinction between dogmatic truths, theological/philosophical truths and scientific truths. He argues that since there are certain aspects of God that you can't have any knowledge about (the "dogmas", like the Holy Trinity), you must have faith in order to believe in it. This is of course the most classic misinterpretation of Jesus' teachings if you're a fan of non-duality.
In non-duality, there is no separation between God and his creation, and the Holy Trinity (the nature of God) can be understood through direct experience. It can also be translated across different metaphysical traditions:
Christianity — the Father + Son + the Holy Ghost.
Hinduism — Brahman + Shiva + Shakti.
Aristotle — "The unmoved mover" + form + matter.
Non-duality — The Absolute + potentiality (emptiness, static being) + actuality (energy, dynamic being) (or The Absolute + the relative).
It's also fun to read about the pre-Socratic philosophers and their version of non-duality (Parmenides, Heraclitus) and similar insights later on (Descartes, Spinoza). Reading about very old philosophers in general is a big mindfuck, because it's so hard to imagine how they truly perceived the world and what they really meant by their theories. There are so many modern presuppositions you have to set aside in order to even begin to sympathize (for example the concept of "substance"). It's impossible in a way, because all of that shapes your perception. It's a great exercise in imagination.

You call it nihilism because it seems meaningless for you, but I want you to notice how it can only be meaningless from a human survival perspective; a perspective which only sees meaning in the perpetuation of its own agenda. What is really meaningless about an infinitely complex dance of trillions of molecular machines, interacting with eachother and rearranging themselves and their environment in an ineffable display of creativity?
When I say "just a bunch of cells", I don't mean to be reductionistic or to subtract meaning from the equation. What I'm really saying is "but what about the cells?". The mistake would be to look at the phenomena of "animal" from a gross surface level view and forget the immense density of stuff happening at the micro and meta-macro levels. The mistake would be to not see the vast web of relationships in reality and how each part is dependent on the other. There is an absolute necessity in everything being just as it is, right now and forever. It's a perfect design.

You can also look at this from the perspective of neuropharmacology. The mind-body system generally downregulates the effect of exogenous stimuli (things coming from the outside) in order to maintain homeostasis (balance between internal and external).
For example, taking a drug that releases excess dopamine (say amphetamine) downregulates the body's own production of dopamine in order to reduce the excess dopamine signalling, leading to what is called "dependence". When you stop taking the drug and the duration is over, you'll have less dopaminergic activity in the areas that were previously experiencing excessive stimulation (come-down, withdrawal).
If we assume that dopamine plays a role in happiness, then you haven't actually "received" happiness from the outside by taking the drug. You've only traded short-term increase in dopamine for a long-term decrease, and you've also traded away your own ability to regulate dopamine signalling. You've only made your happiness more dependent on fleeting conditions (which are also progressively fleeting, because over time you need to take more of the same drug for the same effect, approaching infinity).
More importantly, your ability to be flexible in your functioning; to be alert and activitated in one moment, and calm and relaxed in another, diminishes. There is a selective numbing effect, because the drug only borrows the body's own mechanisms and resources in order to have an effect. You don't gain anything in the long run; you only externalize your own internal control and decrease dynamic responsivity. The changes are not self-consistent, and there is no potential for growth on its own, only degeneration.
To maintain a steady source of happiness, you want to "upregulate the regulatory capacity of the system". Instead of introducing more stimuli from exogenous sources, you increase your endogenous ability to respond to those stimuli. You work with the ebbs and flows of homeostasis by promoting resilience and stability. It's a long-term growth mindset and is the essence of spirituality and holistic health.
You start by looking at the base of the system and work bottom-up, being aware of natural cycles, systematically eliminating dysfunctional behaviors and promoting growth (get enough sleep, physical exercise, remove dietary poisons, eliminate mental trauma, train mental alertness etc.).
From this point of view, unhappiness simply stems from your own inability to regulate your own system. That is essentially the same as saying that happiness comes from within.

I see that many here think they are enlightened already and share what worked for them. I like that, but maybe none of them are enlightened, or a few are, or all are. And sometimes Leo chime in and say something like "you guys haven't even seen God's tits yet, keep going", and they will be like "but Leo, I'm nothing! There is no one here to keep going", and then they just agree to disagree