(Previous posts [1], [2], [2.5],[3] & [4] )
Extending analogy between biological and social memories, it is possible to draw parallel between the situations when both the faculties do not function as desired.
But first, there is one more deviation that can be added to the abnormality of memory (as discussed in one of the previous posts). This is false memory, this is memories of events which never happened, this is again indication of some trauma or shock.
Coming back to civilization, there are times when memories atrophy. Before that a note of caution memories stabilize civilization, they do not make it impervious or eternal. However vigorous the civilization might be, it is bound to decline at some point, the best the memories can do is to act as seed of rejuvenation.
Now the memories atrophy when the process whereby new memories are created ceases. This happens when the intellect, the creative constituency of civilization declines. This may be due to,
a) The material decline of the civilization, when the production and trade declines due to geopolitical factors, dependant societies wither. I assume something like this happened to Harappan civilization (more accurate description may be Saraswati Civilization).
b) The intellect and the creative accomplish the task when they have a well defined (and respectable) position in the hierarchy which sustains them. However if this position or the whole hierarchy is undermined, these decline.
c) When rituals and traditions restrict restrict mobility and society becomes stagnant.
Now the first cause is beyond domain of human influence and hence outside the scope of this discussion.
Second cause deserves a more detailed analysis.
The social fabric can be riven from outside by foreign invasions. Again there can be a foe so overwhelming and resolute against which mightiest effort are futile, at that point one can surrender or take a last stand depending on what are the conditions. But many the times the foe is comparable in military power and it is the lack of political unity and presence of infighting and intrigues, which does the society in. These conditions indicate both decline of moral virtues among the ruling elite (Kshatriya) and the inherent flaw of political institutions.
The social fabric can also be sundered by internal uprisings and revolution. This has less to do with elite than with discontent of masses. This implies either the inherent injustice in the system, or a mismatch between ethos of elite and masses. Most of communist revolution point to the former, while religious persecution in Europe points to the latter.
Third point is more complicated
There is another aspect with the memories, the most persistent mode of memory is as rituals and tradition. These are formed by the most potent action of the instincts and hence survive for the longest duration. A big drawback of this is that they remain even when they are outdated.
I stated earlier that intellect drives the creation of memory, but here intellect was used in the sense the instinct to think, even this instinct is conditioned by social norms. It is necessary that it be distinguished from the ability to reason. Reason is more than a instinct, it is a system of thinking.
The second problem is that any shift in the configuration of forces implies disadvantage to the group(s), usually the predominant or the elites, it is but natural then these groups will seek to resist any change, a very effective way to eliminate any challenge to hegemony is to prescribe rituals and rites which in effect restrict any potential challenge and at the same time amplifies the actual power wielded by status-quoits. This results in proliferation of rites and inflexibility of system.
This, I believe, can explain in part, the rigid caste system, this I believe also explains a gargantuan bureaucracy.
Associated with the atrophy are closely related phenomena, loss of memory, denial and manufacturing of false memory.
These again are analogous to the phenomena manifested in individual humans.
First two tendencies are usually the result when a society or civilization is re-ordered on basis of a new set of ethos and ideas, which is a radical departure from the traditional values.
This might happen when either an external conqueror imposes his values over the vanquished population. Other possibility is when a radical social movement (usually alien to the traditions of host civilization) supersedes over the prevailing social norms. The time this process takes depends on the robustness of the host civilization. Islamic conquests for the large part are examples of the former and spread of Christianity in Europe of later.
Denial on the other hand occurs when the old civilization even though vanquished still maintain their presence, the new order unable to eliminate old memories, ignores or actively suppresses them. In this it is somewhat similar to case of false memories. A typical example of this is Pakistan. Basically what we have here is a society in dilemma, caught in between two conflicting identities, the urge to belong to one identity is the driver behind this suppression. Usually this suppression is society wide. But there is other case which should be discussed in the end.
False memory on the other hand is a device to protect the collective ego and self-identity (again much like as in case of individuals). It has two forms, one to shift the blame, or to boost the esteem. One example of former is how one major component of Islamic identity is victimization with blame shared by US/Israel/loss of Andalusia/unrighteous caliphs. Example of later is how Muslims who are non-Arabs invent lineage originating from Arab.
Last is the case for denial which applies in case of India, this time too there is active suppression of memories, but this is not driven by conflict between civilizations. This happens when some pernicious, where pernicious implies that it harms evolution and leads to decline of society, ideal
infects the psyche, as is not hard to see that the very first section which is infected by this is of intellectuals. Which will explain why seduced by the ideologies of universalism of 20Th century our intellectuals on one hand actively create a false picture of Indo-Pak bonhomie and on the other hand pine for a socialist utopia.
It is this disease of the intellect, and obfuscation of civilization's memory, which is hardest to counter, because this malaise is internal.