Correction: Before Critical Thinking, 'Value Judgements'
I'd like to revise my earlier position on critical thinking: thought is a two-level process, and critical thinking is an 'activated' second level above the base 'weighing and comparing options' function that governs most of our decision making. I had made it sound earlier as though critical thinking was our entire thought process.
I like to call this emotion-led 'weighing and comparing options' process 'value judgements'. As I noted earlier, every memory we store is associated with an emotional response neurone; this is how we determine the 'value' of that memory (otherwise any object or experience, a loved one or apple, would have the same 'weight' in our minds). When confronted with a situation, the mind a) recalls similar situations (and attributing elements) then b) 'weighs' each memory recalled by the strength/resonance of their respective signal against each other; the most 'positive match' and 'appropriate' response will win out, which will lead the brain to send the signals/chemical responses needed for the decided course of action.
This is not critical thinking; it is a 'comparative memory' process. It includes even 'new' situations, as data from sensory input becomes a comparable memory as soon as it is stored, even temporarily.
Critical Thinking from an Evolutionary Point of View
I keep referring to the hunter-gatherer period in which we spent most of our evolution. Much of our time then was spent foraging and hunting, and our clan camps a place to keep and protect our young in larger groups (against nature); without the latter, there would be no point in even having a village. So, most of our time was spent outside of its protection, one-on-one with nature (and at war with other clans).
The latter situation was where critical thinking was most important and most-used: it was a survival tool more than a key to inventiveness. It allowed us, instead of following the same patterns again and again (like 'dumb' animals), to create that 'other option' that would allow us to break our predictability and 'trick' our opponent (that is stuck in their 'known behaviour' thought-process, unable to read our minds)... and this is the main reason we survived as a species through the ages, the ability to break a predictable pattern.
This tool is practically useless in a village (clan camp) environment. Only the results of it could be brought back there in the form of stories that could be remembered and later imitated by other clan members. People then did not share or pass on information for the simple ideal of posterity, but in the aim of survival, and the techniques passed to others were probably dictated by the evolving environment and survival needs therein; it is possible that many techniques faded to oblivion when no longer required by nature or war, which meant that human life was an e'er-evolving, often repeating, state of constant adaptation.
Agriculture to the Cities
This basic evolution still more or less holds true, but our invention of agriculture changed everything. Critical thinking was reserved for that (and even then, it evolved very little; choosing the best grains from each crop is not a process of invention) and the defence of a growing village (and methods of attacking others). Once needed for everyone who affronted nature, critical thinking was practiced by a very few, and these either became the village/city leaders or were allied with them, and the 'common villagers' were left to imitate and 'value judgement' reason within the educative limits defined by the leadership.
Even this holds true today. The only change was, probably after centuries of this follower-imitating-leadership behaviour, an idle group of ambitious yet idle observers discovered that a human could be dependant on leadership for even value judgements; like critical thinking, these also were survival tools for an individual against nature, but in a protective village environment, even these became optional. In short, the former 'protect and educate' village environment that, in hunter-gatherer times, was only applicable in early life (before an adult was obliged leave and fend for itself against nature), became a lifelong process for those who gave up, or were prevented from, making value judgements for themselves. All religions and totalitarianist regimes have their root in this.
The Enlightenment through Today
The invention of writing, and widespread literacy, changed everything yet again. No longer was authority and education the responsibility of a select few (who could only pass it on orally), but people could share information amongst themselves, and judge it for themselves; still, the prevalent authoritarian system, and societal pressure, prevented people from doing this, although these roadblocks to personal, individual enlightenment has eroded slowly over the years. The few critical thinkers practicing science and critical thought in general could record its experimentations for posterity (and validation by anyone able to think for themselves from later generations)... this too was a game-changer, which is why so many libraries went up in totalitarian/religion-lit flames throughout history.
The invention of the internet, though, changes everything yet yet again. We are in the age of information, but this time, an information that can only with difficulty be banned or burned. For the first time in human history, absolutely everyone has not only access to this information, but the invitation to assess and test it for themselves: doing so requires not only the will to make value judgements for oneself, but also critical thinking. With access to this information, a growing human will develop these abilities naturally; this explains the recent surge of activity in those seeking to make young humans disbelieve, and even fear, the possibility of thinking for oneself.
We are at a crossroads of two extremities today: Either fundamentalist 'uni(non)thought' wins out and the distribution of information is controlled or banned, or, for the first time in human history, humans will be using their 'outside the village' abilities, once again as individuals, to judge their own actions, and each others', for themselves, within the village confines.
If the latter were to happen, we will be becoming a real, less leadership-'thought'-dependant, post-modern society. As we once did against nature, once again we will decide rationally (not through peer-pressure imitation), but this time as both individuals and a group, what's best for ourselves.